2d 3d Motion Designer Space Telescope Institute
JWST
JWST (James Webb Space Telescope)
Concept Launch Observatory Sensor Complement Spacecraft Bus and Sunshield
Development Status Spinoff Technologies Feature Stories Supernova Study
How to Weigh a Black Hole References
JWST is an orbiting optical observatory and a key element in NASA's Origins Program, optimized for observations in the infrared region of the electromagnetic spectrum. It is considered the successor mission of HST (Hubble Space Telescope) while operating over a different spectral range. At the NIR and MWIR wavelengths, it benefits from operating at intrinsically lower backgrounds than any comparably sized telescope on the ground. JWST, previously known as NGST (Next Generation Space Telescope), will be the premier space facility for astronomers in the decade following its launch. The overall objectives are to study the first stars and galaxies after the big bang. Major science goals (themes) of the mission are to find answers to the following questions: 1) 2)
• What is the shape of the Universe?
• How do galaxies evolve?
• How do stars and planetary systems form and interact?
• How did the Universe built up its present chemical/elemental composition?
• What is the nature of dark matter?
The radiation from the very distant objects to be observed is practically all in the infrared region. Many of the early events happened when the Universe was between 1 million and 1 billion years old, a period that is not known to earthlings (the dark ages of the Universe). To accomplish the goals of the science themes, the main JWST design requirement calls for the detection of objects up to 400 times fainter than those observable by current ground-based or spaceborne observatories.
Historical background: Large next-generation projects with high-performance observation requirements take about two decades (and more) from first studies to launch. Initial planning for the new mission started in 1989 (visions, conceptual studies). The goal was to have a successor mission for HST ready for launch well before 2010.
In the mid-1990s, a telescope design with an 8 m aperture was considered. The challenge was to come up with a lower cost for the large telescope than for previous much smaller space telescopes. This involved conceptual studies by industry. In 1996, a committee report was written, based on these studies: "Next Generation Space Telescope, Visiting a Time When Galaxies Were Young." This report established also a roadmap to NGST activities, defining the new building blocks and to search for enabling technologies and concepts - in particular in the fields of large-aperture lightweight mirrors that are actively controlled, of advanced detector designs, of suitable cooling techniques for all critical components, and of precision metrology to achieve the goal of measuring ultra precise stellar positions.
A broad range of talent on a national and international level and from many institutions, academia and industry was directly involved in the NGST detailed definition phase (Phase A) including simulations and feasibility studies. In 1997, an ad hoc Science Working Group was formed which came up with thematic science goals and developed a so-called "Design Reference Mission" (DRM), representing a hypothetical suite of key science observing programs [stating the expected physical properties (number density and brightness), the desired observation modes (wavelength band, spectral resolution, number of revisits), and a minimum operational life of 2.5 years to complete the mission] for NGST - which provided a yardstick for technology testing. DRM was and is the primary tool against which any JWST architectures are being measured. The shear complexity of the project and the performance requirements demanded a technology development and validation strategy to address and demonstrate a critical path to a workable design of the mission. 3) 4) 5) 6)
In 2000/1, the NGST project experienced a rescoping of the telescope size (from 8 m aperture to 6.5 m) to keep projected costs in bounds. There were also some technology maturity uncertainties.
The project started in 2002 with a Mission Definition Review. NASA began to realize that the critical technologies had reached a level of sufficient maturity to justify a go-ahead with the next phase of the project.
In September 2002, NASA renamed NGST to JWST (James Webb Space Telescope) in honor of James E. Webb (1906-1992), NASA's second administrator during the Apollo Program of the 1960s (1961-1968). At the same time in Sept. 2002, NASA awarded the prime contract of the JWST observatory development (spacecraft, telescope, integration and testing) to Northrop Grumman Space Technology (formerly TRW) of Redondo Beach, CA.
In the fall of 2003 ICR(Initial Confirmation Review) was given, starting the Phase B of the JWST project. The C/D Phase started in 2008.
The CDR (Critical Design Review) of the JWST (James Webb Space Telescope) is planned for December 2013 (Ref. 31).
Project partners: NASA leads an international partnership in the joint JWST mission that includes ESA (European Space Agency) and CSA (Canadian Space Agency). Both agencies (ESA, CSA) collaborated in the JWST project already at an early planning stage (1996). Aside from instrument contributions, ESA will also launch the JWST spacecraft on an Ariane 5 launcher as agreed to with NASA. NASA/GSFC is managing the JWST project, while STScI (Space Telescope Science Institute) of Baltimore, MD, is responsible for JWST science and mission operations, as well as ground station development (STScI is the same organization that is operating the Hubble Space Telescope). A formal JWST and LISA (Laser Interferometer Space Antenna) cooperation agreement between NASA and ESA was signed on June 18, 2007 at the International Paris Air Show at Le Bourget, France. 7) 8) 9) 10) 11)
A most interesting and valuable side effect of the technology development effort for JWST is that these new technologies will also be available to many other space projects (astronomy, space science, Earth observation, etc.) providing potentially a quantum step in observation performance.
Mission concept:
The JWST mission concept is an ambitious and most challenging development program, requiring a lot of innovative technology introduction as well as conceptual breakthroughs on various levels to meet the proposed observational performances. The objectives of the science themes can only be met by a combination of a large-aperture telescope in space (6.5 m φ ), a very low detection temperature to eliminate noise, and an ideal observing environment (elimination of stray light).
The observatory will be shielded from the sun and Earth by a large deployable sunshade, the entire telescope assembly will be passively cooled to about 37 K, giving JWST exceptional performance in the near-infrared and mid-infrared wavebands. The baseline wavelength range for the instrumentation is 0.6 - 28 µm, and the telescope will be diffraction-limited above 2 µm. The sensitivity of the telescope will be limited only by the natural zodiacal background, and should exceed that of ground-based and other space-based observatories by factors of 10 to 100,000, depending on the wavelength and type of observation. The JWST observatory will have a 5 year design life (with a goal of 10 years of operations) and will not be serviceable by astronauts (as is Hubble). The total mass of JWST at launch is estimated to be 6,500 kg.
Like Hubble, the JWST will be used by a broad astronomical community to observe targets ranging from objects within our Solar System to the most remote galaxies seen during their formation in the early universe.
Major enabling technologies are:
• Large deployable and lightweight beryllium mirrors (a folding 6.5 meter mirror made up of 18 individual segments, adjustable by cryogenic actuators). To fit inside the launch vehicle, the large space telescope prime mirror must be folded in sections for launch, then unfolded (deployed) precisely into place after launch, making it the first segmented optical system deployed in space.
• Deployment of large structures. Once in space, the multilayer sunshield that was folded over the optics during launch will deploy to its full size and keep the telescope shadowed from the sun.
• Introduction of MEMS technology to the microshutter system of the NIRSpec instrument. The programmable microshutters to allow object selection for the spectrograph.
Overview of payload instruments:
• NIRCam (Near-Infrared Camera), funded by NASA with the University of Arizona as prime contractor. CSA is participating in the development of the NIRCam instrument.
• NIRSpec (Near-Infrared multi-object Spectrograph), funded by ESA with EADS Astrium GmbH as prime contractor (the detector arrays and a micro-shutter are supplied by NASA/GSFC)
• MIRI (Mid-Infrared Camera-Spectrograph) a joint instrument of JPL and ESA. The instrument (about 50%) is being provided by ESA member states, coordinated but not funded by ESA.
• FGS (Fine Guidance Sensor) with TFI (Tunable Filter Imager), funded by CSA (Canadian Space Agency)
Figure 1: Photometric performance of JWST instruments as compared to those of current observatories (image credit: STScI)
Legend to Figure 1: Plotted is the faintest flux for a point source that can be detected at 10 sigma in a 104 s integration. The fluxes are given in Janskies as well as AB magnitudes. 12)
Figure 2: Comparison of JWST light gathering power vs spectral range with Hubble and Spitzer telescopes (image credit: STScI) 13)
Launch: ESA, NASA and Arianespace have jointly defined 18 December 2021 as the target launch date for Ariane 5 flight VA256. This third Ariane 5 launch of 2021 will fly the James Webb Space Telescope to space from Europe's Spaceport in French Guiana. 14)
- Important milestones of the launch program for Webb have already been passed or are approaching, such as the final mission analysis review for its launch, the shipment of the Ariane 5 launch vehicle elements from continental Europe to French Guiana, and the scheduled shipment of Webb to French Guiana by the end of September 2021.
- Webb is an international partnership between NASA, ESA, and the Canadian Space Agency (CSA). As part of the international collaboration agreement, ESA is providing the telescope's launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service. Besides that, ESA is contributing the NIRSpec instrument and a 50% share of the MIRI instrument, as well as personnel to support mission operations.
Figure 3: Artist's animation of the James Webb Space Telescope (Webb), folded in the Ariane 5 rocket during launch from Europe's Spaceport in French Guiana (image credit: ESA/ATG medialab)
- "ESA is proud that Webb will launch from Europe's Spaceport on an Ariane 5 rocket specially adapted for this mission. We are on track, the spaceport is busy preparing for the arrival of this extraordinary payload, and the Ariane 5 elements for this launch are coming together. We are fully committed, with all Webb partners, to the success of this once-in-a-generation mission," said Daniel Neuenschwander, ESA Director of Space Transportation.
- "We now know the day that thousands of people have been working towards for many years, and that millions around the world are looking forward to. Webb and its Ariane 5 launch vehicle are ready, thanks to the excellent work across all mission partners. We are looking forward to seeing the final preparations for launch at Europe's Spaceport," said Günther Hasinger, ESA Director of Science.
• As of 01 July 2021, the international James Webb Space Telescope has passed the final mission analysis review for its launch on an Ariane 5 rocket from Europe's Spaceport in French Guiana. 15)
- This major milestone, carried out with Arianespace, the Webb launch service provider, confirms that Ariane 5, the Webb spacecraft and the flight plan are set for launch. It also specifically provides the final confirmation that all aspects of the launch vehicle and spacecraft are fully compatible.
- During launch, the spacecraft experiences a range of mechanical forces, vibrations, temperature changes, and electromagnetic radiation. All technical evaluations performed by Arianespace on the mission's key aspects, including the launch trajectory and payload separation, have shown positive results.
- "We are thrilled to have passed this important step towards the launch of Webb and to have received the green light from Arianespace and NASA," says Peter Rumler, ESA Webb project manager.
- Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, ESA is providing the observatory's launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service.
Figure 4: Webb and Ariane 5: a fit made perfect. Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA). Webb's partners are working towards the launch readiness date of 31 October 2021. The precise launch date following 31 October depends on the spaceport's launch schedule and will be finalized closer to the launch readiness date (image credit: ESA)
- Ariane 5 has been customized to accommodate all the specific requirements of the Webb mission. New hardware ensures that venting ports around the base of the fairing remain fully open. This will minimize the shock of depressurization when the fairing jettisons away from the launch vehicle.
- Some elements of Webb are sensitive to radiation from the Sun and heating by the atmosphere. To protect it after the fairing is jettisoned, Ariane 5 will perform a specially developed rolling maneuver to avoid any fixed position of the telescope relative to the Sun.
- Additionally, an extra battery is installed on Ariane 5 to allow a boost to the upper stage after release of the telescope, distancing it from Webb.
- Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service.
Figure 5: Webb's journey to L2. Webb will orbit the second Lagrange point (L2), 1.5 million km from Earth in the direction away from the Sun. There, its sunshield can always block light and heat from both the Sun and Earth from reaching its telescope and instruments. L2 is not a fixed point, but follows Earth around the Sun (image credit: ESA)
• June 2, 2021:The launch of the NASA/ESA/CSA James Webb Space Telescope (Webb) on an Ariane 5 rocket from Europe's Spaceport in French Guiana is now planned for November 2021. 16)
- American and European officials acknowledged June 1 that the launch of the James Webb Space Telescope will likely slip from the end of October to at least mid-November because of delays linked to the Ariane 5.
- At an ESA briefing about the space telescope, representatives of the agency and Arianespace said they were finalizing reviews to correct a payload fairing problem found on two Ariane 5 launches last year that had grounded the rocket since August. Arianespace described the issue last month as "a less than fully nominal separation of the fairing" on those two launches.
- "The origin of the problem has been found. Corrective actions have been taken," Daniel de Chambure, acting head of Ariane 5 adaptations and future missions at ESA, said. "The qualification review has started, so we should be able to confirm all that within a few days or weeks."
- He did not elaborate on the problem or those corrective actions, beyond stating that the problem took place during separation of the payload fairing. Industry sources said in May that, on the two launches, the separation system imparted vibrations on the payload above acceptable limits, but did not damage the payloads.
- The issue is not linked to a modification to the payload fairing required for JWST. Arianespace has been testing new vents on the fairing designed to reduce the pressure differential once the fairing is separated and thus reduce the loads on the spacecraft. "The issue of the modification of the venting system and the fairing anomaly are different," de Chambure said.
- The Ariane 5 is scheduled to make its next launch, the first since the August 2020 launch that had the payload fairing anomaly, in the second half of July, said Beatriz Romero, JWST project manager at Arianespace. That launch will be the first of two commercial Ariane 5 launches before the JWST launch.
- At a May 11 media event, Greg Robinson, program director for JWST at NASA Headquarters, said that the JWST launch would take place about four months after the first of the two commercial Ariane 5 launches ahead of it. That would push the launch, currently scheduled for no earlier than Oct. 31, to at least the middle of November.
- At the ESA briefing, Thomas Zurbuchen, NASA associate administrator for science, offered a similar schedule. Asked if a mid-November launch was likely, based on 10-week launch processing schedule that begins with JWST's shipment from California to the launch site in French Guiana in late August, he said that timeframe is "approximately correct."
- "We want to be sure that we launch exactly when we're ready, not a day earlier," he said. "That is, when the spacecraft is ready and when the rocket and the fairing and everything is ready."
NASA is targeting Oct. 31, 2021, for the launch of the agency's James Webb Space Telescope from French Guiana, due to impacts from the ongoing coronavirus (COVID-19) pandemic, as well as technical challenges. 17)
This decision is based on a recently completed schedule risk assessment of the remaining integration and test activities prior to launch. Previously, Webb was targeted to launch in March 2021.
• NASA's James Webb Space Telescope currently is undergoing final integration and test phases that will require more time to ensure a successful mission. After an independent assessment of remaining tasks for the highly complex space observatory, Webb's previously revised 2019 launch window now is targeted for approximately May 2020.
- "Webb is the highest priority project for the agency's Science Mission Directorate, and the largest international space science project in U.S. history. All the observatory's flight hardware is now complete, however, the issues brought to light with the spacecraft element are prompting us to take the necessary steps to refocus our efforts on the completion of this ambitious and complex observatory," said acting NASA Administrator Robert Lightfoot.
- Testing the hardware on the observatory's telescope element and spacecraft element demonstrate that these systems individually meet their requirements. However, recent findings from the project's Standing Review Board (SRB) indicate more time is needed to test and integrate these components together and then perform environmental testing at Northrop Grumman Aerospace Systems in Redondo Beach, California, the project's observatory contractor.
- NASA is establishing an external Independent Review Board (IRB), chaired by Thomas Young, a highly respected NASA and industry veteran who is often called on to chair advisory committees and analyze organizational and technical issues. The IRB findings, which will complement the SRB data, are expected to bolster confidence in NASA's approach to completing the final integration and test phase of the mission, the launch campaign, commissioning, as well as the entire deployment sequence. Both boards' findings and recommendations, as well as the project's input, will be considered by NASA as it defines a more specific launch time frame. NASA will then provide its assessment in a report to Congress this summer.
- NASA will work with its partner, ESA (European Space Agency), on a new launch readiness date for the Ariane 5 vehicle that will launch Webb into space. Once a new launch readiness date is determined, NASA will provide a cost estimate that may exceed the projected $8 billion development cost to complete the final phase of testing and prepare for launch. Additional steps to address project challenges include increasing NASA engineering oversight, personnel changes, and new management reporting structures.
- This is a pivotal year for Webb when the 6.5-meter telescope and science payload element will be joined with the spacecraft element to form the complete observatory. The spacecraft element consists of the tennis-court-sized sunshield, designed by Northrop Grumman, and the spacecraft bus, which houses the flight avionics, power system, and solar panels. Because of Webb's large size, engineers had to design components that fold origami-style into the Ariane 5 rocket's fairing configuration.
- Webb has already completed an extensive range of tests to ensure it will safely reach its orbit at nearly one million miles from Earth and perform its science mission. As with all NASA projects, rigorous testing takes time, increasing the likelihood of mission success.
- "Considering the investment NASA and our international partners have made, we want to proceed systematically through these last tests, with the additional time necessary, to be ready for a May 2020 launch," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate.
- After the successful test performance of Webb's telescope and science payload in 2017 at NASA's Johnson Space Flight Center in Houston, the telescope element was delivered to Northrop Grumman earlier this year. Both halves of the 13,500-pound observatory now are together in the same facility for the first time.
- The spacecraft element will next undergo environmental testing, subjecting it to the vibrational, acoustic and thermal environments it will experience during its launch and operations. These tests will take a few months to complete. Engineers then will integrate and test the fully assembled observatory and verify all components work together properly.
- Webb is an international project led by NASA with its partners, ESA and the Canadian Space Agency. ESA is providing the Ariane 5 as part of its scientific collaboration with NASA.
- The James Webb Space Telescope will be the world's premier infrared space observatory and the biggest astronomical space science telescope ever built, complementing the scientific discoveries of NASA's Hubble Space Telescope and other science missions. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.
Table 1: NASA statement of Release 18-019 of 27 March 2018 regarding the new launch target of May 2020 for JWST
Figure 6: James Webb Space Telescope Launch and Deployment (video credit: NASA, Northrop Grumman) 18)
• April 6, 2018: NASA has assembled members of an external Independent Review Board for the agency's James Webb Space Telescope. The board will evaluate a wide range of factors influencing Webb's mission success and reinforce the agency's approach to completing the final integration and testing phase, launch campaign, and commissioning for NASA's next flagship space science observatory.
- "We are exploring every aspect of Webb's final testing and integration to ensure a successful mission, delivering on its scientific promise," said Thomas Zurbuchen, Associate Administrator for NASA's Science Mission Directorate. "This board's input will provide a higher level of confidence in the estimated time needed to successfully complete the highly complex tasks ahead before NASA defines a specific launch time frame."
- The board, convened by NASA's Science Mission Directorate, includes individuals with extensive experience in program and project management, schedule and cost management, systems engineering, and the integration and testing of large and complex space systems, including systems with science instrumentation, unique flight hardware, and science objectives similar to Webb.
- The Independent Review Board review process will take approximately eight weeks. Once the review concludes, the board members will deliver a presentation and final report to NASA outlining their findings and recommendations, which are expected to complement recent data input from Webb's Standing Review Board. NASA will review those findings and then provide its assessment in a report to Congress at the end of June. Northrop Grumman Aerospace Systems, the project's observatory contractor, will proceed with the remaining integration and testing phase prior to launch.
The board consists of the following notable leaders in the space science community:
Mr. Thomas Young, NASA/Lockheed Martin in Bethesda, Maryland – Retired (Chair)
Dr. William Ballhaus, Aerospace Corporation in El Segundo, California- Retired
Mr. Steve Battel, Battel Engineering, Inc. in Scottsdale, Arizona
Mr. Orlando Figueroa, NASA Headquarters and Goddard Space Flight Center in Greenbelt, Maryland – Retired
Dr. Fiona Harrison, Caltech University in Pasadena, California
Ms. Michele King, NASA Office of Chief Financial Officer/Strategic Investments Division in Washington, DC
Mr. Paul McConnaughey, NASA/Marshall Space Flight Center/Webb Standing Review Board (Chair) in Huntsville, Alabama
Ms. Dorothy Perkins, NASA Goddard Space Flight Center in Greenbelt, Maryland - Retired
Mr. Pete Theisinger, Jet Propulsion Laboratory in Pasadena, California
Dr. Maria Zuber, Massachusetts Institute of Technology in Cambridge, Massachusetts
Table 2: Independent Review Board of JWST 19)
• Dec. 17, 2015: The next great space observatory took a step closer this week when ESA signed the contract with Arianespace that will see the James Webb Space Telescope launched on an Ariane 5 rocket from Europe's Spaceport in Kourou in October 2018. The contract includes a cleaner fairing and integration facility to avoid contaminating the sensitive telescope optics. 20)
- With a 6.5 m diameter telescope, the observatory must be launched folded up inside Ariane's fairing. The 6.6 ton craft will begin unfolding shortly after launch, once en route to its operating position some 1.5 million km from Earth on the anti-sunward side.
Orbit:
The orbit of JWST has been selected to be at L2. The spacecraft will be in a Lissajous (or halo) orbit about the Lagrangian point L2. In the Sun‐Earth system the L2 point is on the rotating Sun-Earth axis about the same distance away as L1 (1.5 million km, representing 1/100 the distance from Earth to the Sun) but at the opposite side of the Earth. The L1 location is inside the Earth orbit while the L2 location is outside the Earth orbit.
The halo orbit of JWST is in a plane slightly out of the ecliptic plane. This orbit avoids Earth and moon eclipses of the sun. The halo orbit period is about 6 months. Nominal station keeping maneuvers will be performed every half orbit (i.e. in intervals of about 3 months).
Figure 7: Locations of the five Lagrangian points in the Sun-Earth system
The L2 location is considered to offer the most advantageous viewing for astronomical targets (looking toward the universe) due to nearly constant lighting conditions (minimum of stray light). Another advantage of the L2 location is that it offers a stable thermal environment. The telescope is kept in perpetual shadow by looking into the deep space direction. The deep space provides a 2.7 K black body radiation. This ideal heat sink is being used to provide the passive cooling for the payload to a temperature range of about 37 K, shielded from sunlight (entering the spacecraft from the opposite direction) by a five-layer sunshield [passive cooling is the most elegant and economical method available to obtain the required operating temperatures for infrared detection].
Figure 8: Overview of JWST trajectory to L2 (image credit: NASA)
Figure 9: Artist's rendering of the JWST observatory (image credit: NASA)
JWST deployment sequence:
During the transfer orbit to L2 different elements of the JWST will be deployed and commissioning will start. The observatory has five deployment stages involving the following elements: 21)
1) Deployment of spacecraft appendages (solar arrays, high gain antenna)
2) Deployment of the sunshield (unfolding 2 days after launch)
3) Extension of the tower
4) Deployment of the secondary mirror (positioned on a tripod structure)
5) Deployment of the primary mirror wings
The deployment of the solar arrays and the high gain antenna is scheduled for the first day to provide the capabilities of onboard power generation and a spacecraft communications link. The unfolding of the sunshield will occur two days after launch, while the timeline for secondary and primary mirror deployment is foreseen after four days. "First light" will occur about 28 days after launch, initiating wavefront sensing and control activities to align the mirror segments. Instrument checkout will start 37 days after launch, well before the final L2 orbit insertion is obtained after 106 days. This is being followed by full commissioning procedures expected to last until about 6 months after launch. 22)
Figure 10: Deployment sequence of the OTE (image credit: NASA, STScI)
Observatory
The Observatory architecture is comprised of three elements: OTE (Optical Telescope Element), ISIM (Integrated Science Instrument Module), and the spacecraft (bus and sunshield). A key aspect of the JWST architecture is the use of semi-rigid primary mirror segments mounted on a very stable and rigid backplane composite structure. The architecture is referred to as "semi-rigid" because it has a modest amount of flexibility that allows for on-orbit compensation of segment-to-segment radius of curvature variations. 23) 24) 25) 26) 27) 28) 29) 30) 31)
Figure 11: The three elements of the JWST flight segment (image credit: NASA) 32)
Figure 12: The JWST spacecraft, reflecting the addition of the trim flap and the new solar panel array (image credit: NASA)
| Item | Feature | Benefit |
| OTE | - TMA (Three Mirror Anastigmatic) design, f/20, 25 m2 collecting area | - Superior image quality over the ISIM FOV, provides science resolution and sensitivity |
| Primary mirror | - Primary mirror deploys in two steps (2-chord fold) | - Highly reliable deployment |
| Secondary mirror | - Tripod configuration for support structure | - Provides rigidity, minimizes obscuration and scattered light into the field of view |
| Aft optics | Fixed baffle | Reduces stray light and houses the tertiary mirror and the FSM |
| ISIM | - Simple semi-kinematic mount; 8 m2 of thermal radiators, and 19.9 m3 volume. | - Provides a simple interface for the ISIM to decouple ISIM development from the OTE |
| Tower | - Integral 1 Hz passive vibration isolators | - Reduces S/C dynamic noise onto OTE/ISIM |
| Sunshield | - 5 layer "V" groove radiator design reduces solar energy to a few 10's of mW | - Provides a stable thermal environment for passively cooling the OTE and the ISIM |
| S/C bus | - Chandra-based attitude control subsystem | - Flight-proven low noise dynamic environment that minimizes line-of-sight jitter |
Table 3: Overview of key design features and benefits of the Observatory
| Parameter | Capability | Parameter | Capability |
| Wavelength | 0.6 - 29 µm. Reflective gold coatings | Orbit | Lissajous orbit about L2 |
| Sensitivity NIRCam | - SNR=10, integration time = τi, R=λ/Δλ and Zodicial of 1.2 times that at north ecliptic pole | Celestial sphere coverage Overall | - 100% annually - Observatory ~80.7% |
| Spatial | - Encircled Energy of 75% at 1 µm for 150 mas radius | Mission life | - 5-year minimum lifetime |
| Telescope FOV | - 166 arcmin x 166 arcmin FOV | Launch | 2019 |
Table 4: Overview of the predicted performance of the JWST observatory
OTE (Optical Telescope Element):
The OTE is of course the key element of the observatory with a primary mirror aperture diameter of 6.5 m. A lightweight design is mandatory to keep the launch costs in bounds. Early in the JWST program, an AMSD (Advanced Mirror System Demonstrator) project was launched to address the feasibility and readiness level of the required enabling technologies.
The following requirements were placed on JWST's optics (based on an "optical telescope element" study of 1996:
• The mirror should be sensitive to 1-5 µm (0.6-30 µm extended)
• It should be diffraction limited to 2 µm
• It will have to operate in the temperature range of 30-60 K
• It should have an areal density of < 15 kg/m2.
Figure 13: Isometric drawing of the OTE telescope structure (image credit: NASA, STScI)
The JWST prime contractor, NGAS (Northrop Grumman Aerospace Systems) in consultation with the JWST Telescope Team, selected the beryllium-based mirror technology design made by BATC (Ball Aerospace & Technologies Corporation) as the primary mirror material with the following features: 33) 34)
• 1.318 m point-to-point light-weighted beryllium semi-rigid mirror (element size)
• 13.4 kg/m2 beryllium substrate areal density
• 19.3 kg/m2 areal density for the mirror system - including mirror, reaction structure, flexures, and actuators
• A SBMD (Subscale Beryllium Model Demonstrator) element achieved a 19 nm rms "surface roughness" at 38 K.
Beryllium was chosen over glass as the mirror material because it is lighter and has a low coefficient of thermal expansion at cryogenic temperatures. Since JWST is an infrared telescope, it must operate at cryogenic temperatures (< 40 K) so that the heat of the telescope does not interfere with the radiation it captures. Beryllium mirrors have a heritage in past astronomy missions such as in IRAS (InfraRed Astronomical Satellite, launch Jan. 25, 1983), COBE (Cosmic Background Explorer, launch Nov. 18, 1989) and the Spitzer Space Telescope (launch Aug. 25, 2003). The material properties of beryllium are known to temperatures of 10 K.
Aside from its lightweight features, the primary mirror must be segmented, so that it can be folded up to fit into the nose cone of a rocket. Once on orbit, the telescope will be deployed, using motors to unfold the primary mirror and other important assemblies. Then the telescope will be cooled down from room temperature to about 37 K by the ambient environment on its way to L2 - a temperature change of about 300 K is experienced which obviously causes misalignments and figure errors of the optics system. Note: Passive cooling is attained by placing the observatory at L2 and keeping the telescope and its instrumentation in perpetual shadow by means of a large deployable sunshade.
The primary mirror design consists of 18 hexagonal segments (1.315 m flat-to-flat side), in two rings around the center, resulting in a 6.5 m flat-to-flat diameter with a collecting area of 25 m2. A TMA (Three Mirror Anastigmatic) design is employed with a Strehl ratio of ~0.84 at λ = 2 µm providing a very low background noise. The telescope has an effective f/number of f/16.67, and an effective focal length of 131.4 m.
The segments of the primary mirror act as a single mirror when properly phased relative to each other. The phasing is achieved via a 6 DoF (Degree of Freedom) rigid body motion of the individual segments, and an additional control for the segment mirror radius of curvature. The 18 segments have three separate segment types (A, B, C) with slightly different aspheric prescriptions depending on placement as shown in Figure 14. The numbers 1 to 6 represent the six-fold symmetry of the hexagonal packing of the primary mirror.
Figure 15 shows the rear portion of the mirror segments and the seven actuators. The architecture is "semi-rigid" because it has a modest amount of flexibility that allows for on-orbit compensation of segment-to-segment radius of curvature (ROC) variations. This ROC adjustment is made independent of any attachment to the backplane structure to prevent mirror distortion.
The six actuators providing rigid body motion are arranged in three bipods to form a kinematic attachment to the backplane. Each bipod attaches to a triangular shaped structure which is attached to the isogrid structure of the mirror segment. This structure spreads the loads over the surface of the mirror. The other end of the actuators attaches through a secondary structure and flexure to the backplane. The seventh actuator controls the segment radius of curvature and is independent of the rigid body actuators. The actuators operate at cryogenic and ambient temperatures, and have both coarse and fine positioning capability. This configuration enables simple rigid body motion of the segments without distorting the segment surface. 35)
Figure 14: Arrangement and designation of primary mirror segments and images of the mirrors (image credit: NASA, BATC)
Legend to Figure 14: JWST completes the gold coating of it's telescope mirrors with segment C1. A microscopically thin layer of gold maximizes the reflectivity of these mirrors to infrared light.
Figure 15: Backside of the primary mirror with the three bipod actuators (image credit: NGAS)
WFS&C (Wavefront Sensing and Control) subsystem: A WF&C semi-rigid structure is being used for phasing (to counteract the misalignments). WFS&C consists of actuators mounted on the telescope primary mirror segments and on the secondary mirror, to deform and displace the critical telescope optics in ways that are very effective in compensating the likely on-orbit deformations. The WFS&C software processes images from the cameras to measure the optical aberrations. The software then computes actuator commands to correct the aberrations.
Figure 16: Illustration of the OTE subsystems/assemblies (image credit: NASA, STScI) 36)
Operating temperatures: The large sunshade will protect the telescope from heating by direct sunlight, allowing it to cool down to temperatures of < 45 K. The near-infrared instruments will work at about 30 K through a passive cooling system. The mid-infrared detectors will work at a temperature of 7 K, using stored cryogen (active cooling).
Figure 17: Conceptual layout of the OTE and interfaces to ISIM (image credit: NGAS, STScI)
Figure 18: As at the end of 2013, all 18 of the JWST primary mirror segment assemblies are complete and have arrived at Goddard, where they are being stored inside separate stainless steel shock-absorbing canisters until it is time for mirror assembly (image credit: NASA)
ISIM (Integrated Science Instrument Module)
The ISIM provides structure, environment, control electronics and data handling for three modular science instruments: NIRCam, NIRSpec, and MIRI, and the observatory FGS (Fine Guidance Sensor). ISIM is being provided by NASA/GSFC. In addition to designing the ISIM structure, NASA Goddard provides other infrastructure subsystems critical for the operation of the instruments, including the ISIM Thermal Control Subsystem; ISIM Control and Data Handling Subsystem; ISIM Remote Services Unit; ISIM Flight Software; ISIM Electronics Compartment, and ISIM Harness Assemblies. 37) 38) 39) 40) 41)
ISIM is a distributed system consisting of cold and warm modules.
• The cryogenic instrument module is integrated with the OTE and the sensor complement, all of which are passively cooled to the cryogenic temperature of 39 K. This passively cooled cryogenic (39 K) section houses the instruments NIRCam, NIRSpec, MIRI and the FGS (Fine Guidance Sensor). The MIRI instrument is further cooled by a cryocooler to 7 K.
• The second area is the IEC (ISIM Electronics Compartment), which provides the mounting surfaces and a thermally-controlled environment for the instrument control electronics (region 2 maintained at 298 K). The ICE package is mounted onto the exterior of the ISIM structure.
• The third area (warm module) is the ISIM Command and Data Handling (ICDH) subsystem, which includes ISIM flight software, and the MIRI cryocooler compressor and control electronics (region 3 maintained at 298 K). The warm region of ISIM is located in the spacecraft on the warm side of the Observatory. This more benign environment allows for relaxed thermal requirements on major portions of the electronics with higher power dissipation, and it avoids unnecessary heat loads in the cold section.
Figure 19: ISIM is the science instrument payload of JWST (image credit: NASA) 42)
Figure 20: Components of the integrated ISIM with the FGS mounted inside the structure (image credit: NASA)
Each ISIM instrument reimages the OTE focal plane onto its FPA (Focal Plane Array) assembly, allowing for independent selection of detector plate scale for sampling of the optical PSF (Point Spread Function). A fine steering mirror (FSM) is used for accurate optical pointing and image stabilization. The FSM is located at the image of the pupil, after the tertiary mirror but forward of the focal plane interface to the ISIM. The FSM, coupled with the low structural noise spacecraft, suppresses line-of-sight jitter to allow diffraction-limited performance at 2 µm. The V1, V2, and V3 coordinate systems are defined by the vertex of the primary mirror as shown in Figure 17.
The four scientific instruments onboard JWST are contained in the ISIM (Integrated Science Instrument Module) which is mounted to the BSF (Back Plane Support) behind the primary mirror. ISIM contains four instruments: MIRI,FGS/IRISS, NIRCam, and NIRSpec. The IEC (ISIM Electronics Compartment) is also mounted to the BSF and holds a number of high-power boxes, totaling 200 W of dissipation, at room temperature on the cold side of the sunshield. This is an order of magnitude above the summed dissipation of the remainder of the cold side. Its proximity to the cryogenic instruments is driven by the noise-sensitive science data that must be processed by electronics with the IEC. 43)
The IEC has been designed to hold room-temperature electronics boxes in close proximity to the cryogenic telescope and instrument module and to direct the 200 W dissipation so that is does not have a negative affect on the observatory performance. This is made possible through multiple radiative isolators in series, conductive isolation, and directional baffles. Analysis has shown that this design will meet the requirements levied on the IEC by the observatory, allowing the IEC to function as an integral part of the James Webb Space Telescope.
Figure 21: ISIM components within the Observatory (image credit: NASA)
| Instrument | Spectral range (µm) | Optical elements | FPA | Plate scale | FOV (Field of View) |
| NIRCam (Short | 0.6 - 2.3 | Fixed filters | Two 2 x 2 mosaics of 2048 x 2048 arrays | 32 | 2.2' x 4.4' |
| NIRCam (Long | 2.4 - 5.0 | Fixed filters | Two | 65 | 2.2' x 4.4' |
| NIRSpec (prism, | 0.6 - 5.0 | Transmissive slit mask: | Two | 100 | 3.4' x 3.1' |
| NIRSpec (Grating, | 1.0 - 5.0 | ||||
| NIRSpec (IFU, | 1.0 - 5.0 | IFU (Integrated Field Unit) | 3.0" x 3.0" | ||
| MIRI (Imaging) | 5 - 28 | Broad-band filters, | 1024 x 1024 | 110 | 1.4' x 1.9' |
| MIRI (Prism | 5 -10 | R ~ 100 | |||
| MIRI | 5 - 28 | Integral field spectrograph | Two 1024 x 1024 | 200-470 depending on band | 3.6" x 3.6" to |
| FGS | 1.5 – 2.6 | Order-blocking | 2048 x 2048 | 68 | 2.3' x 2.3' |
Table 5: Overview of science instrument characteristics
The ISIM instruments are located in an off-axis position, which yield excellent image quality over the 9.4 arcminute field, as shown by the contours of residual wavefront error as a function of field location in Figure 24. The cold portion of the ISIM is integrated with the OTE.
Figure 22: Schematic diagram of the accommodation of the four science instruments in ISIM (image credit: NASA)
Figure 23: NASA engineers check out the unwrapped ISIM structure in a clean room in 2009 (image credit: NASA) 44)
Figure 24: ISIM focal plane allocation layout (image credit: STScI, NASA)
Legend to Figure 24: Placement of the ISM instruments in the telescope field of view. The field of view of each instrument is fully contained within the instrument allocation regions. The numbers indicate the wavefront error contribution by the optical telescope element (in nm) at each location.
Figure 25: The cryogenic portion of the ISIM system (left) is shown in its test configuration (right) for the CV-1RR (image credit: NASA)
Legend to Figure 25: A high fidelity simulation of the JWST telescope beam is fed from below into the ISIM by an Optical SIMulator (OSIM) that is mounted on vibration isolators. The SES vacuum vessel is equipped with nitrogen and helium shrouds to enable testing at the 40 K nominal flight operating temperature. 45)
The ISIM structure and assembly has a total mass of ~ 1400 kg which is about 23% of the JWST mass.
ISIM status:
• Summer 2015: The ISIM enters this final testing sequence in its full flight configuration. After some precursor integration and test activities, which included two very successful cryo-vacuum campaigns (called CV1-RR and CV2, the latter of which was in a nearly-final configuration), the ISIM underwent a series of activities to upgrade its instruments and systems to full flight readiness. These activities included: 46)
- Completion of the upgrade of the near-infrared detector arrays in NIRCam, NIRSpec, and FGS/NIRISS to a newer, more robust design that eliminates a dark current degradation mechanism suffered by the earlier generation arrays.
- Installation of new Microshutter Arrays in the NIRSpec with improved stability against the acoustic loads of launch.
- Installation of new grisms in the NIRISS instrument, including a new grism for exoplanet spectroscopy with 2-3 times higher throughput than the original optic.
- Upgraded electronics boards in several instruments for improved performance or reliability.
- Installation of the flight cold head of the MIRI cryocooler system (the Heat Exchanger Stage Assembly, mounted to the ISIM structure).
The first phase of this final environmental test sequence, vibration testing, was completed in June 2015, with vibration of the "ISIM prime" module. Sinusoidal sweep testing was carried out in each of three axes, with amplitudes up to ~2.5g in some frequency bands, in order to verify workmanship by subjecting the system to the low frequency structural dynamic spectrum of the launch environment.
Figure 26: The ISIM structure and flight instruments, re-integrated and ready for environmental testing (image credit: NASA, Chris Nunn)
Sensor complement: (NIRCam, NIRSpec, MIRI, FGS/NIRISS)
NIRCam (Near-Infrared Camera)
NIRCam funded by NASA with the University of Arizona as prime contractor (PI: Marcia J. Rieke). CSA is participating in the development of the NIRCam instrument. The industrial partner is Lockheed-Martin Advanced Technology Center, Palo Alto, CA. The NIRCam objectives are: 47) 48) 49) 50) 51) 52)
• To find "first light" sources. NIRCam surveys will become the backbone of the first light searches and for galaxy evolution studies.
• To assist the space telescope in initial (after deployment) and periodic alignment tests throughout the mission. This requires wavefront sensing to assure perfect alignment and shape of the different primary mirror segments.
• The camera also includes features for studying star formation in the Milky Way and for discovering and characterizing planets around other stars.
The various roles place additional constraints on the camera design. First, the camera must accommodate extra optics and pupil analyzers to enable the wavefront sensing. Secondly, the modules incorporating the wavefront sensing must be fully redundant as the mission depends critically on this functionality. Hence, the NIRCam design includes two identical imaging modules each of which includes dual filter wheels. The dual filter wheels are configured so that one wheel holds bandpass filters while the other wheel holds pupil analyzers thus permitting wavefront analysis as a function of wavelength.
NIRCam employs a compact refractive optics design using dichroics (to split the incoming radiation in 2 wavelengths) to enable simultaneous observation of a field at λ < 2.5 µm and at λ > 2.5 µm. The short wavelength module is Nyquist-sampled at 2 µm while the long wavelength module is Nyquist-sampled at 4 µm.
| Wavelength range | 0.6 - 5.0 µm |
| Spectral resolution | Selection of R~4 and R~10 discrete filters, R~100 using 2 tunable filters |
| FOV (Field of View) | Imaging: 2.16 x 2.16 arcmin at two wavelengths simultaneously |
| Spatial resolution | Imaging: 0.0317 arcsec/pixel, λ<2.5µm; 0.068 arcsec/pixel, λ > 2.5µm |
| Coronagraphy | Choice of coronagraphic spots and pupils in all instrument sections |
Table 6: Overview of the NIRCam capabilities
| Parameter | Imaging module 1 | Imaging module 2 | Tunable filter module short λ | Tunable filter module long λ |
| Wavelength range (µm) | 0.6 to 2.3 | 0.6 to 2.3 | 1.2 to 2.5 | 2.5 to 4.5 |
| Nyquist sampling (µm) | 2 / 4 | 2 / 4 | 4 | 4 |
| Pixel format | 4096 x 4096 (short λ) | 4096 x 4096 (short λ) | 2048 x 2048 | 2048 x 2048 |
| FOV (arcmin) | 2.3 x 2.3 | 2.3 x 2.3 | 2.3 x 2.3 | 2.3 x 2.3 |
| Spectral resolution | 4, 10 | 4, 10 | 100 | 100 |
Table 7: NIRCam module characteristics
Figure 27: Schematic layout of a NIRCam imaging module (image credit: NASA)
Figure 28: Schematic of NIRCam coronagraphic design (image credit: STScI)
Legend to Figure 28: An optical wedge in the pupil wheel brings the coronagraphic spots into the field of view. The spots are matched with Lyot stops.
Coronagraphy: To enable the coronagraphic imaging of nearby stars, each of the two identical optical trains in the instrument also contains a traditional focal plane coronagraphic mask plate held at a fixed distance from the FPAs (Focal Plane Assemblies), so that the coronagraph spots are always in focus at the detector plane. Each coronagraphic plate is transmissive, and contains a series of spots of different sizes to block the light from a bright object. Each coronagraphic plate also includes a neutral density spot to enable centroiding on bright stars, as well as point sources at each end that can send light through the optical train of the imager to enable internal alignment checks. Normally these coronagraphic plates are not in the optical path for the instrument, but they are selected by rotating into the beam a mild optical wedge that is mounted in the pupil wheel (Figure 28), which translates the image plane so that the coronagraphic masks are shifted onto the active detector area (Ref. 36).
Figure 29: Layout of a NIRCam imaging module (image credit: University of Arizona)
The NIRCam filters and pupil selections are given in Table 8. All of the camera's filter wheels are identical, 12 position dual wheels. NIRCam also includes a set of broadband filters whose wavelengths and widths have been carefully chosen to support accurate photometric redshift estimation.
| Position | Shortwave imaging | Longwave imaging | Tunable filter | |||
| Filter wheel (µm) | Pupil wheel | Filter wheel (µm) | Pupil wheel | Filter wheel | Pupil wheel | |
| 1 | B1: 0.7 | Imaging pupil | B5: 2.7 | Imaging pupil | Blocker-1 | Imaging pupil |
| 2 | B2: 1.1 | Flat field source | B6: 3.6 | Flat field source | Blocker-2 | Flat field source |
| 3 | B3: 1.5 | Outward pinholes | B7: 4.4 | Outward pinholes | Blocker-3 | Outward pinholes |
| 4 | B4: 2.0 | Coron pupil 1 | I4: 2.4-2.6 | Coron pupil 1 | Blocker-4 | Coron pupil 1 |
| 5 | I1: 1.55-1.7 | Coron pupil 2 | I5: 2.8-3.2 | Coron pupil 2 | Blocker-5 | Coron pupil 2 |
| 6 | I2: 1.7-1.94 | HeI 1.083 µm | I6: 3.2-3.5 | TBD | Blocker-6 | Cal pattern 1 |
| 7 | I3: 2.0-2.22 | WFS-1 (Wavefront Sensing) | I7-CO2: 4.3 | TBD | Blocker-7 | Cal pattern 2 |
| 8 | B8: 0.8-1.0 | WFS-2 | I8-CO: 4.6 | TBD | Blocker-8 | Cal pattern 3 |
| 9 | Hα: 0.656 | WFS-3 | Brα: 4.05 | TBD | Blocker-9 | Cal pattern 4 |
| 10 | [Fell] 1.64 | WFS-4 | H2: 2.41 | TBD | 1%-1 | TBD |
| 11 | Pα: 1.875 | WFS-5 | H2: 2.56 | TBD | 1%-2 | TBD |
| 12 | H2: 2.12 | WFS-6 | H2: 4.69 | TBD | 1%-3 | TBD |
Table 8: Specification of NIRCam filters and pupils
Figure 30: Illustration of the NIRCam instrument (image credit: NASA)
The expected point-source sensitivity is ~3.5 nJy for wavelengths from 0.7 - 5 µm in a 100,000 second exposure at a SNR (Signal-to-Noise Ratio) of 10. All ten detectors arrays needed for NIRCam are using Teledyne Technologies (former Rockwell Scientific )HgCdTe 2k x 2k devices (HAWAII-2RG detector technology, also referred to as H2RG). The short wavelength bands will be sampled at 4096 x 4096 pixels (0.0317 arcsec/pixel), while the long wavelength bands are being sampled by 2048 x 2048 pixels (0.0648 arcsec/pixel). The focal plane array includes detector and cryogenic electronics. 53) 54)
Note: The term "Jy" refers to the "Jansky," the unit of radio‐wave emission strength, in honor of Karl G. Jansky (1905‐1950) an American engineer whose discovery of radio waves (1931) from an extraterrestrial source inaugurated the development of radio astronomy. Jansky published his findings in 1932 while working at Bell Telephone Laboratories in Murray Hill, NJ.
The "Jy" is a unit of radiative flux density (or radio‐wave emission strength) which is commonly used in radio and infrared astronomy. 1 Jy = 10‐26 W/(m2 Hz). The units of Jy (Hz)‐1/2 then refer to the noise power.
Figure 31: This new 2Kx2K pixel NIRCam sensor chip assembly incorporates improved barrier layers to increase the ground storage lifetime (image credit,NASA, Bernie Rauscher, "JWST Detector Update," Ref. 45)
Legend to Figure 31: The Teledyne H2RG detectors are being used in 3 instruments of JWST, namely in NIRCam, NIRSpec, and in FGS/NIRISS.
The NIRCam coronagraph: Each NIRCam module will be equipped with a simple Lyot coronagraph consisting of a selection of focal plane occulters and pupil masks (Lyot stops). The requirements are:
1) Provide imaging to within 0.6 arcsec (4λ/D) of the star at λ = 4.6 μm and to within 0.3 arcsec at λ = 2.1 μm for the detection of extrasolar planets seen in emission.
2) Provide imaging to within 0.8 arcsec (6λ/D) of the star at λ = 4.3 μm, 0.64 arcsec at λ = 3.35 μm, and 0.4 arcsec at λ = 2.1 μm for observations of circumstellar disks seen in reflected light.
3) The occulters must be rigidly mounted and must not interfere with imaging during non-coronagraphic observations, requiring placement outside the normal field of view.
4) Ideally, suppress the diffraction pattern produced by the JWST obscurations to a level equal to or below the scattered light created by the uncorrectable optical surface errors, given the budgeted ~131 nm rms of wavefront error prior to the coronagraphic occulters.
5) Provide sufficient throughput to image 1 Gyr-old Jupiter-mass planets around the nearest late-type stars with 1-2 hours of exposure time.
6) Tolerate 2% pupil misalignments due to pupil wheel positioning errors and telescope-to-instrument rotational offsets.
7) Tolerate 10-40 marcsec (milliarcsecond) of pointing error at λ = 4.6 μm without a significant decrease in performance.
NIRCam status:
• Jan. 6, 2015: The MIRCam instrument surpassed expectations during tests in late 2014. NIRCam performed significantly better than requirements during the first integrated, cryogenic testing program at GSFC (Goddard Space Flight Center), Maryland. 55)
- In April 2014, NASA installed the instrument alongside others in the ISIM (Integrated Science Instrument Module), which finished cryogenic and vacuum testing late last year.
• Flight NIRCam ready for integration into ISIM (Ref. 192).
NIRSpec (Near-Infrared multi-object Spectrograph)
NIRSpec is funded by ESA (Project Scientist: Peter Jakobsen of ESA/ESTEC) with Airbus Defince and Space (formerly EADS Astrium GmbH) as prime instrument contractor (the detector arrays and a microshutter are supplied by NASA/GSFC). The key objectives are the study of galaxy formation, clustering, chemical abundances, star formation, and kinematics, as well as active galactic nuclei, young stellar clusters, and measurements of the initial mass function of stars (IMF). 56) 57) 58) 59) 60) 61) 62)
The region of sky to be observed is transferred from the JWST optical telescope element (OTE) to the spectrograph aperture focal plane (AFP) by a pick-off mirror (POM) and a system of foreoptics which includes a filter wheel for selecting band passes and introducing internal calibration sources. The nominal scale at the AFP is 2.516 arcsec/mm.
Figure 32: CAD layout of the NIRSpec instrument with outer shroud removed (image credit: ESA)
The NIRSpec baseline design uses a micro-electromechanical system (MEMS), consisting of an array of about 1000 x 500 microshutters, to select hundreds of different objects in a single field of view.
The NIRSpec instrument will be the first slit-based astronomical MOS (Multi-Object Spectrograph) in space providing spectra of faint objects over the near-infrared 1.0-5.0 µm wavelength range at spectral resolutions of R=100, R=1000 and R=2700. The instrument's all-reflective wide-field optics, together with its novel MEMS-based programmable microshutter array slit selection device and its large format low-noise HgCdTe detector arrays (2 detectors of 2 k x 2 k pixels), combine to allow simultaneous observations of > 100 objects within a FOV of 3.4 arcmin x 3.6 arcmin with unprecedented sensitivity. 63) 64) 65)
Figure 33: Schematic layout of the NIRSpec optics (image credit: ESA)
NIRSpec is required to select various spectral band widths and split these up into its comprised wavelengths. These functions are achieved by the FWA (Filter Wheel Assembly) and the GWA (Grating Wheel Assembly). The filters of the FWA select a different bandwidth of the spectrum each while the gratings on the GWA yield specific diffractive characteristic for spectral segmentation. A high spectral sensitivity as well as the ability to detect the spectra of various objects at the same time result in high requirements regarding the positioning accuracy of the optics of both mechanisms in order to link the detected spectra to the 2-dimensional images of the observed objects. 66)
The spectrometer uses diffractive gratings to spatially separate the incoming light and analyze several objects simultaneously. The NIRSpec mechanism yields 6 different gratings and one prism to work with various spectral resolutions and in different ranges of the infrared spectrum. A TAM (Target Acquisition Mirror) allows allocation of the spectra and the corresponding stellar objects. These 8 optical elements are integrated on a GWA (Grating Wheel Assembly) as shown in Figure 34. It exchanges the diffractive optic within the instrument's beam path with high precision to allow correlation of different spectra taken from the same object.
To avoid the overlap of various orders of diffraction on the detector, a set of spectral filters was designed to select the desired wavelength range. These filters are mounted on a mechanism quite similar to the GWA. It moves one filter into the beam path to build a fitting combination of grating in use and preselected range of wavelength. This FWA (Filter Wheel Assembly) holds four edge filters and two band filters for various wavelengths, one clear filter for target acquisition and a mirror assembly for in-orbit calibration and pupil alignment during integration of the mechanism (Figure 35).
Figure 34: Illustration of the GWA mechanism (image credit: Carl-Zeiss Optronics)
Figure 35: Illustration of the FWA mechanism (image credit: Carl-Zeiss Optronics)
Mechanical alignment: Since both FWA and GWA are mechanisms actively influencing the beam path of the instrument, precise and repeatable alignment of the currently used optic, it is essential to ensure a stable image on the detector. Especially the GWA alignment is crucial since its optic works in reflection where every tilt of the optic is carried over directly into the alignment of the instrument. The FWA on the other hand uses planar elements working in transmission inducing but a fraction of their misalignment into an aberration of the beam (Ref. 66).
NIRSpec includes also an IFU (Integral Field Unit) device with the objective to study of the dynamics of high redshift galaxies. This device provides in addition a NIRSpec backup acquisition mode for spectroscopy. The IFU permits a 2-D spectral characterization of astronomical objects with unprecedented depths, especially in the 2-5 µm wavelength range. The IFU covers a FOV of 3 arcsec x 3 arcsec and provides five fixed slits for detailed spectroscopic studies of single objects. The NIRSpec-IFU is expected to be capable of reaching a continuum flux of 20 nJy (AB>28) in R=100 mode, and a line flux of 6 x 10-19 erg s-1 cm-2 in R=1000 mode at an SNR> 3 in an exposure period of 104 s.
The FPA (Focal Plane Array) consists of sub-units, each 2 k x 2 k, forming an array of 2 k x 4 k sampled at 100 marcsec (milliarcsecond) pixels. The detectors are thinned HgCdTe arrays (ASICs) built by the Rockwell Science Center and referred to as SIDECAR (System for Image Digitization, Enhancement, Control and Retrieval). Each of the two ASICs has 2048 x 2048 pixels, pixel size of 18 µm, pixel scale = 100 mas (micro arcseconds), the data are locally digitized. 67)
The NIRSpec also contains a calibration unit with a number of continuum and line sources.
Figure 36: Illustration of a MSA (Microshutter Array) assembly at left and the FPA SIDECAR ASIC at right, (image credit: NASA)
Multiobject spectroscopy: A special MEMS device, referred to as MSA (MicroShutter Array), is being developed at NASA/GSFC to be used as a programmable field selector for NIRSpec. The objective is to provide a means to observe numerous objects simultaneously and to eliminate the confusion caused by all other sources. MSA consists of microshutter arrays arranged in a 2 x 2 quadrant mosaic. Each quadrant represents a closely packed array of 175 x 384 of shutters each of which may be addressed independently - allowing only the light from objects of interest into the instrument. The MSA covers a FOV of 3.6 arcmin x 3.6 arcmin (each microshutter has a FOV of 0.2 x 0.4 arcsec) - allowing the simultaneous observation of about 100 objects.
The microshutters themselves are MEMS devices produced on a thin silicon nitride membrane on 100 µm x 200 µm pitch (spectral x spatial direction). They are actuated magnetically and latched and addressed electrostatically. The MSA object selection feature represents an enabling technology development with a first introduction in spaceborne astronomy. 68)
Figure 37: Schematic layout of the microshutter assembly (image credit: NASA, ESA)
The MSA microshutter array consists of ust under a quarter of a million individually controlled microshutters. By programming the array to only open those shutters coinciding with pre-selected objects of interest, light from these objects is isolated and directed to the spectroscopic stage of NIRSpec to produce the spectra.
Figure 38: Photo of NASA/GSFC engineers inspecting an MSA with a low light test (image credit: GSFC, Chris Gunn, ESA) 69) 70)
Legend to Figure 38: The inspection light source is held by the technician at the front of the picture. Four array quadrants are located within the octagonal frame in the center of a titanium mosaic base plate.
The team, led by Principal Investigator Harvey Moseley of GSFC has demonstrated that electrostatically actuated microshutter arrays — that is, those activated by applying an specific voltage — are as functional as the current technology's magnetically activated arrays. This advance makes them a highly attractive capability for potential Explorer-class missions designed to perform multi-object observations. 71)
Considered among the most innovative technologies to fly on the Webb telescope, the microshutter assembly is created from MEMS technologies and comprises thousands of tiny shutters, each about the width of a human hair. Assembled on four postage-size grids or arrays, the 250,000 shutters open or close individually to allow only the light from targeted objects to enter Webb's NIRSpec, which will help identify types of stars and gases and measure their distances and motions. Because Webb will observe faint, far-away objects, it will take as long as a week for NIRSpec to gather enough light to obtain good spectra.
Figure 39: Alternate view of the NIRSpec instrument (ESA, NASA)
The NIRSpec instrument has a size of about 1.90 m x 1.3 m x 0.7 m and an estimated mass of about 196 kg.
Figure 40: Photo of the NIRSpec engineering test unit in Oct. 2009 (image credit: ESA)
The spectrograph structure is built from silicon carbide (SiC) - a monolithic ceramic providing the properties to meet the extremely high demands for dimensional stability and geometrical accuracy for the optical assembly. Geometrical distortions between NIRSpec and the ISIM, generated by very high temperature differences between cryogenic operational and ambient on ground environment are balanced by so called Kinematic Mounts made from titanium alloy. The need to exchange these parts without losing optical performance of the already aligned instrument led to the development of a highly sophisticated exchange procedure. 72)
The existing Kinematic Mounts already integrated on the Flight Model of NIRSpec were declared non-flight-worthy due to a detection of a manufacturing issue within the tapered areas, dedicated for flexural bending. Consequently a remanufacturing of the three OBKs (Optical Bench Kinematic Mounts) was decided and the development of an exchange philosophy considering all aspects of safety and technical requirements was developed in a joint team of ESA and Airbus Defence and Space.
Due to the detailed planning, preparation and practice, the actual exchange on the NIRSpec flight hardware was performed in five days without any procedure variation. The exchange was successfully performed as trained before.
The dye penetrant investigations performed in between the individual OBK exchange activities confirmed no damage of the SiC interfaces of the OBBP (Optical Bench Base Plate). These results were backed by acoustic monitoring which showed that no shock was introduced and no crack was initiated inside the SiC structure.
The results of the online optical measurements showed that the relative position and the PAR (Pupil Alignment Reference) remained stable within the measurement accuracy better than 3 acrsec angular and 10 µm relative PAR center displacement.
Status of NIRSpec:
• July 20, 2015: Engineers from Airbus and ESA (European Space Agency) work inside NASA Goddard Space Flight Center's large clean room to remove the cover on Webb Telescope's NIRSpec (Near InfraRed Spectrometer) instrument in preparation for the replacement of the MSA (Micro Shutter Array) and the FPA (Focal Plane Assembly). 73)
• Feb. 2015: The past two months have seen a team of engineers engaged in the intricate activity of replacing key components of the NIRSpec (Near InfraRed Spectrograph) on the James Webb Space Telescope. The instrument is now ready for the next series of extensive environmental tests devised to ensure that JWST's instruments can withstand the stresses and strains of launch and operation in space. 74) 75) 76)
- In the summer of 2014, the JWST Integrated Science Instrument Module (ISIM), fitted with all four instruments (NIRSpec, MIRI, NIRCam, and FGS/NIRISS), successfully completed cryogenic testing in a '24/7' campaign that lasted 116 days.
- However, the positive outcome of this important test campaign did not mean that ISIM and the instruments were ready for integration onto JWST's telescope. It has been known for over a year that additional work would be necessary to get some of the instruments into their final flight configuration. As a consequence, a period of a few months was allocated for these activities, immediately after the completion of the cryogenic test campaign.
- In particular, NIRSpec needed to have its detectors, microshutter assembly and optical assembly cover replaced. Also, the NIRCAM and FGS/NIRISS teams had to exchange some components in their instruments. MIRI was the only instrument that remained integrated with the ISIM. However, MIRI's configuration was also updated by installing the flight model cooler Cold Head Assembly (CHA) and exchanging some of the cooler lines and their supports.
- The first generation of JWST's highly sensitive near-infrared detectors were found to suffer from a design flaw that resulted in a progressive degradation of their performance. New detectors have now been installed in all three near-infrared instruments.
- Another crucial component of NIRSpec are its MSA (Microshutter Assembly), a new technology developed for JWST by NASA. - One of the defining and pioneering features of NIRSpec is its ability to analyze the light from more than 100 astronomical objects at the same time. This is made possible by an assembly of four microshutter arrays, totalling almost a quarter of a million individual shutters.
- One of the defining and pioneering features of NIRSpec is its ability to analyze the light from more than 100 astronomical objects at the same time. This is made possible by an assembly of four MSAs, totalling almost a quarter of a million individual shutters.
- The cryogenic test revealed that several thousand of the individual microshutters had become inoperable and could not be opened. This susceptibility to acoustic noise was not expected and had gone undetected because of the difficulty of reproducing the environment to which the microshutters are actually subjected in this instrument. As a result of this problem, the performance of the microshutters in NIRSpec was strongly degraded. The NIRSpec Engineering Test Unit (ETU) provided the most realistic test environment for the MSA. These various tests provided a wealth of information that helped NASA to identify the cause of the 'failed closed' shutters issue.
- The new MSA contains three 'original design' arrays and one 'new design' array. In addition to most arrays being pre-screened at array level, the complete new MSA flight model was acoustically tested in the NIRSpec ETU before it was installed in the flight version of NIRSpec.
• April 4, 2014: An important milestone for JWST was passed on 25 March with the installation of the NIRSpec instrument on the ISIM (Integrated Science Instrument Module) at NASA/GSFC. All four science instruments are now in place on the ISIM, ready for the next series of tests. 77)
• Feb. 2014: The NIRSpec instrument is being installed on the ISIM (Integrated Science Instrument Module) at Goddard in preparation for an extensive series of tests with the full instrument complement. In addition, new detectors have been selected for NIRSpec, to be installed later this year. 78)
• Sept. 30, 2013: The NIRSpec instrument has arrived at the NASA/GSFC. 79)
• In early September 2013, the NIRSpec instrument, built by Astrium GmbH, was formally handed over to ESA. This marks an important milestone in Europe's contribution to the JWST mission. Having undergone rigorous testing in Europe, NIRSpec will be shipped to NASA later this month for integration into JWST's instrument module, followed by further testing and calibration as the whole observatory is built up. 80)
MIRI (Mid-Infrared Camera-Spectrograph)
MIRI is a joint instrument development of NASA and ESA. The instrument optics module and optical bench will be provided by the European MIRI Consortium funded by the ESA member states. NASA/JPL will provide the remainder of the instrument, notably the detector and cryostat subsystems. Within the joint instrument science team, Gillian S. Wright of the UKATC (UK Astronomy Technology Center), Edinburgh, is the PI of the European MIRI Consortium while George H. Rieke at the Steward Observatory of the University of Arizona (UA) is the MIRI PI for NASA. ESA coordinates the activities of the European MIRI Consortium (21 institutes from 10 countries) while EADS Astrium Ltd. functions as the main instrument contractor. The MIRI instrument has a mass of ~ 103 kg. 81) 82) 83) 84) 85) 86) 87) 88) 89)
Note: The ROE (Royal Observatory Edinburgh) comprises the UKTAC (UK Astronomy Technology Center) of the Science and Technology Facility Council (STSC), the Institute of Astronomy of the University of Edinburgh and the ROE Visitor Center.
Further participating European organizations in the MIRI project are: Astron, The Netherlands; CCLRC, Rutherford Appleton Laboratory (RAL), UK; CEA Service d'Astrophysique, Saclay, France; Centre Spatial De Liège, Belgium; CSIC (Consejo Superior de Investigaciones Científicas), Spain; DSRI (Danish Space Research Institute), Denmark; Dublin Institute for Advanced Studies, Ireland; IAS (Institut d'Astrophysique Spatiale), Orsay, France; INTA (Instituto Nacional de Técnica Aeroespacial), Spain; LAM (Laboratoire d'Astrophysique de Marseille), France; MPIA (Max-Planck-Institut fur Astronomie), Heidelberg, Germany; Observatoire de Paris, France; PSI (Paul Scherrer Institut), Switzerland; University of Amsterdam, The Netherlands; University of Cologne, Germany; University of Leicester, UK; University of Leiden, The Netherlands; University of Leuven, Belgium; University of Stockholm, Sweden.
As part of the European cooperation with NASA on the JWST program, MIRI was set up as a 50 : 50 partnership between ESA and NASA, with the European Consortium (EC) in charge of the optical bench assembly and the JPL (Jet Propulsion Laboratory) in charge of the detector system, the cooling system, and the flight software (Figure 41). In addition to the responsibilities shown, GSFC (Goddard Space Flight Center) provides the harness between the optical module and the ICE (Instrument Control Electronics). The formal delivery of the MIRI Optical System, including the detectors chain provided by JPL, to NASA is the responsibility of ESA.
Figure 41: Overview of MIRI instrument concept, contributions, interfaces and responsibilities (image credit: ESA, NASA)
In contrast to other science missions, where each scientific instrument has its own dedicated computer, on JWST there is one unit for all instruments where the flight software for each instrument resides – the ICDH (Instrument Control and Data Handling) electronics. Failure modes and event upsets are handled in this unit. The ICDH interfaces via an IEEE-1553B (MIL-STD-1553B) bus to the dedicated control electronics for the instrument mechanisms (ICE) and, via a remote services unit, for the FPE (Focal Plane Electronics) unit as shown in Figure 42.
Figure 42: Functional block diagram of MIRI optical and cooler subsystem interfaces (image credit: MIRI consortium)
MIRI's principal science objectives relate to the origin and evolution of all cosmic constituents, in particular to galaxy formation, star formation, and planet formation on a wide range of spatial and temporal scales. MIRI is to provide imaging, coronagraphy and low- and medium-resolution spectroscopy in the mid-infrared band (the 5-28 µm), representing a broad wavelength response in the thermal infrared. To achieve an optimized detection sensitivity, MIRI requires a high photon conversion efficiency as well as spectral and spatial passbands matched to the observation targets.
The MIRI design features an imager and a dual spectrometer (Figure 44). Light enters from the telescope through the IOC (Input Optics and Calibration) module. The IOC is part of the MIRI Optical Bench Assembly. It is designed to pick-off the MIRI field of view from the JWST Fine Steering Mirror and to relay the relevant parts of this FOV into the spectrometer and into the imager subsystems. The IOC additionally provides in-flight calibration fluxes to the imager and is mounted onto the MIRI primary structure (deck) and is operated at about 6 K. The IOC is being provided by CSL (Centre Spatial de Liege) of Liege University, Belgium.
The imager and the two spectrometer modules are based on all reflecting designs. The optical configuration of MIRI supports four science modes:
1) Photometric imaging in a number of bands from 5.6-25.5 µm within a FOV of 1.9 arcmin x 1.4 arcmin
2) Coronagraphy with a spectral range 10-27 µm in 4 bands (10.65, 11.4, 15.5, and 23 µm)
3) Low-resolution (R = 100) resolving power slit spectroscopy of single objects in the spectral range 5-11 µm
4) Medium-resolution (~100 km/s velocity resolution) integral field spectroscopy in the spectral range 5-28.5 µm over FOVs growing with wavelength from 3.5 x 3.5 to 7 arcsec x 7 arcsec.
Figure 43: The MIRI optics module (image credit: MIRI consortium)
The optical concept splits the instrument into two separate channels operating over the 5 to 28 µm wavelength range, one for imaging (over a 1.9 x 1.4 arcmin FOV) and one for medium resolution spectroscopy (up to 8 x 8 arcmin FOV). The functional split into two parts was chosen because it was found that it simplified the internal optical interfaces, and the complexity of the layout and of the mechanisms. Both the imager and spectrometer channels are fed by common optics from a single pick-off mirror placed close to the telescope focal plane, and fed also by a common calibration subsystem. - The pick-off mirror in front of the JWST OTE focal plane directs the MIRI FOV towards the imager. A small fold mirror adjacent to the imager light path picks off the small (up to 8 x 8 arcsec) FOV of the spectrometer. A second tilting fold in the spectrometer optical path is used to select either light from the telescope or from the MIRI calibration system.
Figure 44: MIRI instrument optical bench assembly and key subsystem layout (image credit: MIRI consortium)
The MIRI spectrometer is comprised of two parts, the SPO (Spectrometer Pre-Optics), built by UKATC, and the SMO (Spectrometer Main Optics), built by Astron, The Netherlands. The two parts of the spectrometer combine together using a spectrograph filter wheel which is made by MPIA (Max Planck Institute of Astronomy). The SPO houses the image slicers and the dichroic/grating wheels. Light enters the SPO directly from the IOC. Light passes from the image slicer, through a series of mirrors, to the FPM. The FPM in turn is located in the SMO. 90) 91)
Figure 45: Main optics of the MIRI spectrometer (image credit: MIRI European Consortium)
Figure 46: Illustration of the SPO (image credit: MIRI European Consortium)
The light is divided into four spectral ranges by the dichroics, and two of these ranges are imaged onto each of the two detector arrays. Along the way to the appropriate array, the light is dispersed by a diffraction grating. The gratings are mounted on mechanical turrets with three for each spectral range. A full spectrum is obtained by taking exposures at the three settings of each mechanical turret - the turrets are ganged together and operated with a single mechanism, and the dichroics allow the same spot on the sky to be distributed to all four spectrometer arms. Thus, only three exposures are required to obtain a complete spectrum.
| Channel | 1 | 2 | 3 | 4 |
| Nr of slices (N) | 21 | 17 | 16 | 12 |
| Wavelength range (µm) | 5.5-7.7 | 7.7-11.9 | 11.9-18.3 | 18.3-28.3 |
| Slice width (arcsec) | 0.176 | 0.277 | 0.387 | 0.645 |
| FOV (arcsec) | 3 x 3.87 | 3.5 x 4.42 | 5.2 x 6.19 | 6.7 x 7.73 |
| Resolving power | 2400-3700 | 2400-3600 | 2400-3600 | 2000-2400 |
Table 9: Summary of imager channels
The imager module has a combined FOV for the imager and coronagraph/low-resolution spectrometer modes. The coronagraph masks are placed at a fixed location on one edge of the imager field.
Figure 47: Schematic configuration of the MIRI imager module (image credit: MIRI European Consortium)
Figure 48: Illustration of the MIRI imager (image credit: MIRI European Consortium)
Figure 49: Illustration of the coronagraph (image credit: MIRI European Consortium)
The instrument uses phase mask coronagraphs. They reject the light of a central source by introducing phase shifts using a quadrant-design plate at the instrument input focal plane. These shifts cause the light from the source to interfere destructively at the detector array. Unlike conventional occulting Lyot coronagraphs, phase plates allow measurements to be obtained very close to the central object. Further from the central object, they provide performance similar to that of a conventional occulting coronagraph. The 4-quadrant phase mask is dividing an Airy disk (image of a point source) in the center of the field into 4 domains; and it applies a phase difference of p to two of them, so that the image is eliminated by destructive interference.
The dichroic filter wheel comprises three working positions to move gratings and dichroics simultaneously. Each is located on separate wheel discs. The two wheels feed light in to the four spectrometer channels inside MIRI.
Figure 50: Scheme of the spectrograph filter wheel (image credit: MIRI European Consortium)
Figure 51: Illustration of the dichroic wheel (image credit: MIRI European Consortium)
The filter wheel has 18 positions: 10 imaging filters, 4 coronagraphic diaphragms/filters, 1 neutral density filter, 1 double prism, 1 lens and 1 clear/blind position (counterweight of prism). The system has to operate in the cryo-vacuum of 7 K up to 10 years. The design is of ISOPHOT wheel mechanisms heritage flown on ESA's ISO (Infrared Space Observatory) mission. The filter wheel assembly houses a wheel disc carrying all the optical elements. Rotation is realized by a central two-phase torque motor (allows for bi-directional movement).
Figure 52: Illustration of the filter wheel (image credit: MIRI European Consortium)
The FPS (Focal Plane System) consists of three FPM (Focal Plane Module) units (two in the spectrometer and one in the imager), a single FPE (Focal Plane Electronics) unit, and a set of low noise FPE/FPM cryogenic harnesses that connect the FPMs to the FPE. Each FPM houses a single SCA (Sensor Chip Assembly) containing a 1024 x 1024 Si:As IBC detector array and readout electronics. The IBC (Impurity Band Conduction) technology of Raytheon Vision Systems has been selected for very sensitive, cryogenically cooled infrared detectors. These arrays are manufactured as a hybrid structure, referred to as SCA (Sensor Chip Assembly), consisting of a detector array connected with indium bumps to a ROIC (Readout Integrated Circuit). The Si:As IBC detector material offers the highest performance for longwave detection in low-background systems. 92) 93)
| Wavelength band (µm) | Support mode | Sensitivity (10σ, 10,000 s) |
| 5.6 | Imaging | 0.19 mJy |
| 12.8 | Imaging | 1.4 mJy |
| 25.5 | Imaging | 29 Jy |
| 6.4 | Line spectroscopy | 1.2 x 10-20 W m-2 |
| 22.5 | Line spectroscopy | 5.6 x 10-20 W m-2 |
Table 10: Overview of expected MIRI sensitivities
Figure 53: Schematic of the silicon detector array (image credit: JPL)
Figure 54: The FPM of MIRI (image credit: JPL)
MIRI cryocooler: The MIRI instrument (optical bench, all focal planes) is cooled to ~7 K by a super-frigid mechanical helium cryocooler system of NASA/JPL built by NGAS (Northrop Grumman Aerospace Systems), Redondo Beach, CA. The cryocooling is achieved by means of a cryostat. Two hydrogen vessels are being used, the larger one for the optical bench, and the smaller one for the detectors. The vessels are designed to hold 1000 liter of solid hydrogen at 7 K.
Active cooling is provided by a dedicated three stage Stirling-cycle PT (Pulse-Tube) to precool a circulating helium flow loop, with a Joule-Thomson (JT) expansion stage to provide continuous cooling to 6.2 K to a single point on the MIRI optical bench. Significant development of the cryocooler occurred as part of the ACTDP (Advanced Cryocooler Technology Development Program) prior to selection as the flight cryocooler for MIRI. 94) 95) 96)
Figure 55: Block diagram of the ACTDP design applied to the MIRI cooler subsystem; the dark lines show the He gas flow in the JT cooler loop (image credit: NGAS)
Figure 56: Illustration of the MIRI cryocooler elements (image credit: NGAS, UA, Ref. 89)
Figure 57: Schematic view of the distributed MIRI cryocooler subsystem (image credit: NGAS)
Legend to Figure 57: The drawing on the left side shows the spacecraft bus (bottom) and the OTE. The CCA (Cooler Compressor Assembly) and the CHA (Cold Head Assembly) are shown as expanded CAD renderings on the right hand side. The CCA is shown in context of the spacecraft bus and tower structures in the immediate vicinity. The CCE (Cryocooler Control Electronics) and the CTA (Cooler Tower Assembly) are not shown.
Status of MIRI:
• Feb. 2014: MIRI has performed beautifully during its first cryo-vacuum test campaign carried out at NASA's Goddard Space Flight Center towards the end of 2013. An examination of data recorded during those tests confirms that the instrument is in good health and performing well. 97)
• July 2013: The ISIM, with the two instruments (MIRI and FGS/NIRISS), is now being prepared for the first series of cryogenic tests, planned for later this summer. These will include optical, electrical and electromagnetic interference tests, all under cold vacuum conditions. The tests will be conducted in the SES (Space Environment Simulator) vacuum chamber at GSFC. 98)
• On April 29, 2013, MIRI was the second instrument to be installed into the ISIM (after FGS/NIRISS).
• MIRI arrived at GSFC on 28 May 2012, having been despatched from the Rutherford Appleton Laboratory in the United Kingdom, where it had been assembled. Engineers from ESA, the MIRI European Consortium and NASA were on hand to take delivery of this, the first of JWST's four instruments to arrive at GSFC.
FGS (Fine Guidance Sensor):
The FGS is a sensitive camera that provides dedicated, mission-critical support for the observatory's ACS (Attitude Control System). The camera can image two adjacent fields of view, each approximately 2.4 arcmin x 2.4 arcmin in size, and can also be configured to read out small subarrays (8 x 8 pixels) at a rate of 16 times/s. Even with these short integration times, the FGS is sensitive enough to reach 58 µJy at 1.25 µm (~Jab = 19.5). This combination of sky coverage and sensitivity ensures that an appropriate guide star can be found with 95% probability at any point in the sky, including high galactic latitudes.
The objectives of FGS are to provide constant directional data for the telescope, enabling it to maintain stability for improved image acquisition. Specific requirements are: 99) 100)
1) To obtain images for target acquisition. Full-frame images are used to identify star fields by correlating the observed brightness and position of sources with the properties of cataloged objects selected by the observation planning software.
2) To acquire preselected guide stars. During acquisition, a guide star is first centered in an 8 x 8 pixel window. Small angle maneuvers are then executed to translate this window to a pre-specified location within the FOV, so that an observation with one of the science instruments will be oriented correctly.
3) To provide the ACS with centroid measurements of the guide stars at an update rate of 16 Hz. These measurements will be used to enable stable pointing at the milli-arcsecond level.
Note: In the course of building and testing of the TFI (Tunable Filter Imager) flight model, numerous technical issues arose with unforeseeable length of required mitigation effort. In addition to that, emerging new science priorities caused that in summer of 2011 a decision was taken to replace TFI with a new instrument, called NIRISS (Near Infrared Imager and Slitless Spectrograph). 101) 102)
FGS/NIRISS (Near-Infrared Imager and Slitless Spectrograph):
FGS is one of the four science instruments on board the JWST, a contribution of CSA (Canadian Space Agency). The FGS-NIRISS science team is jointly led by John Hutchings of NRC (National Research Council) of Canada, Victoria, British Columbia, Canada and René Doyon, University of Montréal. - The FGS consists of two Guider channels and one Near-Infrared Slitless Spectrometer (NIRISS) channel. COM DEV Space Systems of Ottawa Canada is CSA's prime contractor for the FGS instrument. The NIRISS channel makes use of grisms and filters optimized for first-light science and exo-planet observations. This is a recent change in the configuration of the instrument which until the summer of 2011 made use of a tunable filter. The block diagram of the updated instrument configuration is shown in Figure 58. 103) 104)
Figure 58: Block diagram of the FGS (image credit: CSA, ComDev Ltd.)
The FGS prime function is to work with the ACS (Attitude Control Subsystem) of the Observatory to provide fine guiding. The guiding side of FGS (FGS-Guider) is a near-infrared (IR) camera operating in broadband light over the full 0.6-5 µm bandpass of its two Hawaii-2RG detectors. The FGS-Guider features an all reflective optical design with two redundant 2.3 arcmin x 2.3 arcmin FOV each capable of reading a small (8 x 8) subarray window to select any star in the FOV and to report its centroid every 64 ms (16 Hz) to the ACS, which in turn sends an error signal to the fine steering mirror of the telescope. At this sampling rate, the FGS-Guider is required to have a NEA (Noise Equivalent Angle) less than 4 marcsec (one axis) on a star with an integrated signal of 800 electrons, equivalent to approximately a JAB = 19:5 star. This limiting magnitude guarantees more than 95% of the sky coverage with at least three stars within the FGS-Guider FOV. 105) 106)
FGS features two modules: an infrared camera dedicated to fine guiding of the observatory and a science camera module, the NIRISS (Near-Infrared Imager and Slitless Spectrograph) covering the wavelength range between 0.7 and 5.0 µm with a FOV of 2.2 arcmin x2.2 arcmin.
A schematic optical layout of NIRISS is shown in Figure 59. The optical design is an all reflective design with gold-coated diamond-turned aluminum mirrors. The average WFE ( Wavefront Error) over the FOV of the instrument (telescope excluded) is less than 79 nm RMS.
Figure 59: NIRISS optical layout. The NIRISS optical configuration is identical to the old TFI one except that the etalon is no longer present and that the dual wheel has been repopulated with new filters and grisms as shown in Figure 60 (image credit: CSA, ComDev Ltd.)
NIRISS has a dual pupil and filter wheel assembly. Collimated light first passes through a selected position in the pupil wheel and then through the selected position in the filter wheel. Figure 60 shows the elements of the pupil and filter wheels. The PAR (Pupil Alignment Reference) shown in Figure 1 is used during ground testing to verify the positioning of NIRISS in the ISIM (Integrated Science Instrument Module). Its presence decreases the throughput of the "CLEARP" element by about 10%. 107)
The Dual Wheel is comprised of pupil and filter wheels, bearings, gears, static hub, rear motor/resolver plate and the support bracket. The equipment includes drive motors, resolvers and variable reluctance sensors. Each wheel (~280 mm diameter) is capable of rotating the optical elements to one of 9 desired positions, supported by a preloaded duplex pair of angular contact bearings. All moving parts use MoS2 dry lubricants compatible with the cryogenic environment. A stepper motor with a single-stage planetary gearhead is used to drive each wheel independently, through a reduction gear train. The optical parts are held in place by a metallic spring gasket with a precision holder machined from Ti 6Al-4V ELI annealed, stress-relieved prior to final machining and cryo-cycled prior to installing optical elements. A black tiodize coating is used for stray light control. 108) 109)
Figure 60: NIRISS dual wheel optical elements (image credit: CSA, COM DEV Ltd.)
Detector: The NIRISS detector consists of a single SCA (Sensor Chip Assembly) with the following characteristics:
- 2048 x 2048 pixel HgCdTe array. Each pixel is 18 microns on a side.
- Dark rate: < 0.02 e-/s
- Noise: 23 e- (correlated double sample)
- Gain: 1.5 e-/ADU
- 2.2 arcmin x 2.2 arcmin FOV
- Plate scale in x: 0.0654 arcsec/pixel; plate scale in y: 0.0658 arcsec/pixel
• The 2048 x 2048 pixels of the SCA are divided into 2040 x 2040 photosensitive pixels and a 4-pixel wide border of non-photosensitive reference pixels around the outside perimeter. The reference pixels do not respond to light, but are sampled and digitized in exactly the same way as the light sensitive pixels. The reference pixels can be used to monitor and remove various low-frequency bias drifts.
• The composition of the detector is tuned to provide a long-wavelength cutoff at approximately 5.3 microns.
• The SCA is fabricated and packaged into a FPA (Focal Plane Assembly ) that includes a HAWAII-2RG readout integrated circuit (ROIC), which is controlled by a SIDECAR ASIC (Application Specific Integrated Circuit). The ASIC is a custom-built chip that clocks the array, sets the bias voltages, and performs the analog-to-digital conversion of the pixel voltages.
• The SCA is fabricated and packaged into a focal-plane assembly (FPA) that includes a HAWAII-2RG readout integrated circuit (ROIC), which is controlled by a SIDECAR Application Specific Integrated Circuit (ASIC). The ASIC is a custom-built chip that clocks the array, sets the bias voltages, and performs the analog-to-digital conversion of the pixel voltages.
• A full-frame read of the SCA is digitized through four readout amplifiers. Each amplifier reads a strip that is 512 x 2048 pixels. 110)
Figure 61: Schematic view of the NIRISS SCA (image credit: STScI)
Observation modes: NIRISS has four observing modes (Ref. 105):
1) BBI (Broadband Imaging) featuring seven of the eight NIRCam broadband filters
2) Low resolution WFSS (Wide-Field Slitless Spectroscopy) at a resolving power of ~150 between 1 and 2.5 µm
3) Medium-resolution SOSS (Single-Object Spectroscopy). The single-object cross-dispersed slitless spectroscopy enabling simultaneous wavelength coverage between 0.7 and 2.5 µm at R~660, a mode optimized for transit spectroscopy of relatively bright (J > 7) stars
4) sparse AMI (Aperture Interferometric Imaging) between 3.8 and 4.8 µm enabling high-contrast (~ 10-4) imaging of M < 8 point sources at angular separations between 70 and 500 marcsec.
Broadband imaging: NIRISS offers the same broadband imaging capability as NIRCam except that NIRISS does not carry the NIRCam F070W filter. The new blocking filters procured for NIRISS, used in combination with NIRCam short wavelength fitters, have measured inband transmission of 95% typically. As shown in Figure 62, NIRISS and NIRCam are predicted to have similar sensitivities within 10%. This sensitivity calculation takes into account the coarser pixel sampling (65 marcsec) of NIRISS at short wavelengths compared to NIRCam (32 marcsec). NIRISS is not expected to be used for broadband imaging unless parallel observing is eventually offered by the Observatory. If so, NIRISS could be easily used in parallel with NIRCam for a wide variety of programs including deep extragalactic surveys aiming at probing the galaxy population of the early universe.
Figure 62: Predicted NIRISS broadband imaging sensitivity (10σ, 104s) compared to NIRCam (image credit: CSA, COM DEV Ltd.)
WFSS (Wide-Field Slitless Spectroscopy): The WFSS mode of NIRISS operation is optimized for Ly α emitters (1-2.5 µm) and makes use of a pair of grisms GR150V and GR150H. In order to break wavelength-position degeneracy two prisms are at 90º angle to each other and are used in two separate imaging sessions. In this scheme, the intersection of the two perpendicular dispersion lines indicates undeviated wavelength and true sky position of the source.
It is implemented through the two GR150R & GR150C grisms operated in slitless mode at R = 150 (2 pixels), enabling low-resolution multi-object spectroscopy between 1 and 2.5 µm in first order. The grisms are resin-replicated on a low refractive index material (Infrasil 301) to minimize Fresnel loss. They were manufactured by Bach Research. The peak efficiency of a flight-like GR150 grism, i.e. manufactured with the same replication process (same substrate prism, same master), was measured to be ~80% (see Figure 63). Wavefront error measured at 90 K on both grism surfaces showed some distortion due to stress induced by CTE (Coefficient of Thermal Expansion) mismatch between the resin and the glass substrate. However, within uncertainties, the distortion was measured to be identical on both sides at 90 K. This distortion effectively turns the grism into a weak meniscus lens which, to first order, has no defocus. Cryogenic (90 K) monochromatic PSF measurements were also secured to estimate the TWFE (Transmitted Wavefront Error) of the GR150 grisms; the results indicate that they should have less than 30 nm (RMS) of TWFE. The image quality in the WFSS mode is therefore expected to be as good as in broadband imaging i.e. with a typical Strehl ratio of ~0.5 at 1.3 µm.
Figure 63: Blaze function of the GR150 grism measured on a flight-like grism. The flight prisms are expected to have very similar performance (image credit: CSA, COM DEV Ltd.)
SOSS (Single-Object Slitless Spectroscopy): This mode of NIRISS operation is optimized for relatively bright stars (e.g. exoplanet transiting systems) in 0.6-2.5 µm spectral range in the first order of dispersion. It is based on a GR700XD grism made of the directly ruled ZnSe. A ZnSe cross-dispersion prism is placed in front of the grism for an optimal separation of the first and second order spectra.
To optimize this mode for very high signal-to-noise ratio observations of bright objects, the entrance face of the ZnSe prism has a built-in cylindrical weak lens that defocusses the spectrum over ~25 pixels along the spatial direction, keeping the point spread function nearly diffraction-limited in the spectral direction. As a result, the spectrum is undersampled at most wavelengths along the spectral direction which, given the non-uniform detector pixel response in the presence of pointing jitter noise, constitutes a potential source of systematic effect for achieving high-precision differential spectrophotometry. To mitigate/minimize this problem, the GR700XD grism is slightly rotated by ~ 2º with respect to the detector. Given that the PSF (Point Spread Function) is spread over 25 pixels in the spatial direction, this rotation effectively provides Nyquist sampling at all wavelengths. Furthermore, since the GR700XD grism is operated in slitless mode, there are no flux variations induced by a slit. All these features, designed for achieving high-precision differential spectrophotometry, combined with the very stable thermal environment expected at L2, will make the NIRISS SOSS mode a powerful capability for atmospheric characterization of transiting exoplanets.
Figure 64: Line-flux sensitivity in the NIRISS WFSS mode for various blocking filters (image credit: CSA, COM DEV Ltd.)
Legend to Figure 64: The dashed line is the predicted NIRSpec sensitivity for the multi-slit low-resolution (R ~100) mode; the solid circles superimposed on the dashed line is the spectral resolution of NIRSpec at that wavelength. The green triangle is the sensitivity that TFI would have had at its shortest wavelength (1.45 µm; zLyα = 10:9); TFI would have been typically a factor ~3 more sensitive than NIRISS at the expense of sampling a very narrow redshift range at a given wavelength and limited to probe zLyα > 10:9.
AMI (Aperture Masking Interferometry): The NIRISS PW includes a seven-aperture non-redundant mask (NRM; Figure 65) used for aperture masking interferometry (AMI). The AMI technique enables high-contrast imaging at inner working angle theoretically as small as 1 λ/2D. This mode is particularly appealing for faint companion detection (brown dwarfs & exoplanets) around relatively bright stars. AMI has been successfully used on the ground for a variety of applications, for example to unveil the spiral structure of the stellar wind of the Wolf-Rayet star WR98A (Monnier et al. 1999), detect brown dwarfs (Lloyd et al., 2006) and to put mass limits on the presence of brown dwarfs and exoplanets within the inner 10 AU of the multi-planetary system HR8799.
Figure 65: NIRISS non-redundant mask design (image credit: CSA, COM DEV Ltd.)
The main scientific application of AMI with NIRISS is for high-contrast imaging of point sources but it can also be used for aperture synthesis applications like probing the inner structure of nearby active galactic nuclei. For the former, simulations suggest that contrast of ~ 2 x 10-4 within one λ/D at 4.3 µm should be achieved on a M = 8 star in 104 seconds. This level of contrast is sufficient to detect 5-10 MJup gas-giant exoplanets around bright nearby young (10-100 Myrs) stars. For comparison, contrast at the level of ~ 10-3 within one λ/D at L0 has been achieved on Keck. Since AMI is particularly sensitive to amplitude errors, a space-based environment is ideal for AMI. The NIRISS simulations take into account the instrumental effect of bad pixels, intra-pixel response and flat field errors and assume one calibrator/reference star; using more than one calibrator should improved the performance. As seen in Figure 12, AMI is probing a unique discovery space between 70 and 500 marcsec which is very complementary to NIRCam and MIRI, both virtually "blind" to companions at separations less than ~0.5 arcsec.
Figure 66: Five sigma contrast curve predicted for the NIRCam/MIRI coronagraphs and the NIRISS/AMI mode. AMI is probing relatively small inner working angles (image credit: CSA, COM DEV Ltd.)
| NIRISS mode | Filters | Grism | Mask |
| BBI (Broadband Imaging) | F090W, F115M, F150W, F200W, F277W, F444W, F356W | ||
| WSS (Wide-Field Slitless Spectroscopy) | F115W, F150W, F200W, F140M, F158M | GR150H or GR150V | |
| SOSS (Single Object Slitless Spectroscopy) | Open | GR700XD | |
| AMI (Aperture Interferometric Imaging) | F380M, F430M, F444W | NMR (Non Redundant Mask) | |
| Pupil Alignment (used only during on- ground testing) | Open | PAR (Pupil Alignment Reference) |
Table 11: Summary of NIRISS filter, grism and mask configurations for different modes of operation (Ref. 101)
FGS/NIRISS integration and status:
• August 27, 2015: Preparations for the third cryo-vacuum test (CV3) of the ISIM (Integrated Science Instrument Module) at NASA's Goddard Space Flight Center continued throughout the summer. For the first time, the flight configuration of the ISIM was vigorously shaken – not stirred! – and bombarded by intense acoustical waves to simulate the harsh conditions of launch. Both NIRISS and FGS sailed through their "system functional tests" before and after these perturbations with no issues. Additional tests to confirm the electromagnetic compatibility of the subsystems of ISIM under conditions that simulate normal operations were also completed successfully. Now that the robustness of the ISIM has been demonstrated, it's "full speed ahead" for the beginning of CV3 in late October! 111)
• Feb. 12, 2015: FGS/NIRISS became the first instrument to be reinstalled in the ISIM (Integrated Science Instrument Module) following the "Half-Time Show." All the planned hardware changes were successfully completed and both instruments passed their electronic check-outs at room temperature with flying colors. FGS/NIRISS is ready for the final series of tests at NASA's Goddard Space Flight Center! 112)
• Oct. 29, 2013: NIRISS completed its first suite of tests under cryogenic conditions in the large vacuum chamber at NASA's Goddard Space Flight Center. The tests featured "first light" observations for all the observing modes of NIRISS. Although a few glitches occurred, initial analysis of the test data show that NIRISS is performing marvelously.
• March 1, 2013: NIRISS and the FGS became the first flight instruments to be attached to the ISIM (Integrated Science Instrument Module), which is currently located in the large clean room at NASA/GSFC (Ref.100).
• Dec. 21, 2012: NIRISS and the FGS successfully completed room-temperature functional tests at NASA/GSFC.
• Nov. 15, 2012: NIRISS and the FGS became the first JWST instruments to be accepted formally by NASA during the Delivery Review Board meeting at the Goddard Space Flight Center.
• The Canadian Space Agency delivered NIRISS and the Fine Guidance Sensor to NASA's Goddard Space Flight Center on July 30, 2012.
• The end-to-end functional and performance cryogenic vacuum testing of NIRISS was successfully completed at the beginning of 2012. The new, compared to TFI, components of the Dual Wheel went through separate qualification process afterwards.
Figure 67: FGS and NIRISS are two instruments in one package (image credit: CSA)
Legend to Figure 67: The left image shows the components of FGS. Light from the telescope is redirected by the POM (Pick-Off Mirror), and refocused by the TMA (Three-Mirror Assembly) onto the Fine Focus Mechanism before entering the detector assembly. The FGS has two detectors, called FPAs (Focal Plane Assemblies), which record the light . — The right image shows the components of NIRISS. Light from the telescope is redirected into NIRISS by its Pick-Off Mirror. The collimator makes the light rays parallel to each other so they pass correctly through various combinations of filters or light-splitting grisms in the Pupil and Filter Wheel. Finally, the light is focused by the camera onto the detector (Ref. 102).
Figure 68: FGS full instrument level test (image credit: CSA, COM DEV Ltd., Ref. 110)
Figure 69: Photo of the fully assembled NIRISS (bottom) and FGS-Guider (image credit: CSA, NASA) 113)
Spacecraft bus and sunshield
The JWST spacecraft bus provides the necessary support functions for the operation of the JWST observatory. The bus is the home for six major subsystems: 114)
• ACS (Attitude Control Subsystem)
• EPS (Electrical Power Subsystem)
• C&DHS (Command and Data Handling Subsystem)
• RF communications subsystem
• Propulsion subsystem
• TCS (Thermal Control Subsystem)
The spacecraft is 3-axis stabilized. Two star trackers (+ 1 for redundancy) point the observatory toward the science target prior to guide star acquisition, and they provide roll stability about the telescope line of sight (V1 axis.) Six reaction wheels (two are redundant) are mounted on isolators near the center of gravity of the bus to reduce disturbances to the observatory. These reaction wheels offload the fine steering control (operation from a 16 Hz update from the FGS) to maintain the fine steering mirror near its central position to limit differential distortion-induced blurring onto the target star. 115) 116)
Figure 70: Top view of the JWST spacecraft bus (image credit: NASA)
Figure 71: Observatory schematic block diagram (image credit: NASA)
A propulsion subsystem, containing the fuel tanks and thrusters, is used to support trajectory maneuvers to L2 and to maintain the halo orbit at L2.
The avionics design of JWST employs the FPE (Focal Plane Electronics) onboard network which uses the SpaceWire specification and a transport layer (not part of SpaceWire). SpaceWire is used to provide point‐to‐point links to ISIM (Integrated Science Instrument Module). A MIL‐STD‐1553 data bus is being used to communicate with the ICEs (Instrument Control Electronics) of each instrument, and FGS (Fine Guidance Sensor).
Figure 72: Various FM (Flight Model) and EM (Engineering Model) components of the JWST spacecraft (image credit: NASA, Ref. 42)
RF communications: JWST will be using CCTS (Common Command and Telemetry System), a modified multimission COTS system of Northrop Grumman which is based on Raytheon's ECLIPSE product line (Raytheon was responsible for developing this system for Northrop Grumman. ECLIPSE is a commercial off-the-shelf command and telemetry product that is configured to support both satellite flight operations and integration and test for JWST. 117)
Onboard storage is provided by a solid-state recorder with a capacity of 58.9 GB (manufacturer: SEAKR Engineering, Inc.). Operating like a digital video recorder, the spacecraft flight unit records all science data together with continuous engineering "state of health" telemetry for the entire observatory 24 hours a day, seven days a week. The data is downloaded to the ground station when the telescope communicates with Earth during a four-hour window every 12 hours. 118)
A high gain antenna provides Ka-band and S-band communications. The Ka-band downlink from L2 is used for science data at the selectable rates of 7, 14, or 28 Mbit/s. A pair of omni-directional antennas (S-band) provide near hemispherical coverage for emergency communications. The S-band nominal downlink is 40 kbit/s and the uplink is 16 kbit/s.
Note: Unlike Hubble, JWST was never meant to be repaired. But in May 2007, NASA announced that it is considering installing a grapple attachment anyway, just to be safe.
Figure 73: JWST communications system architecture (image credit: NASA) 119)
JWST Sunshield:
The sunshield provides a very stable passively cooled cryogenic environment to the OTE and ISIM instrumentation - taking full advantage of the steady thermal conditions of the JWST halo orbit at L2. Thermal stability is further enhanced by the two-chord fold architecture of the primary mirror. The folding architecture allows simple thermal straps across the hinge lines and results in a uniform temperature distribution on the primary mirror structure. With these features, the observatory can maintain its optical performance and optical stability for any pointing within its FOR (Field of Regard) without relying on active thermal control or active wavefront control. The sunshield deployment concept is based on Northrop Grumman's precision antenna mesh system. 120) 121)
The FOR (Field of Regard) is the region of the sky in which observations can be conducted safely at a given time. For JWST, the FOR is a large annulus that moves with the position of the Sun and covers about 40% of the sky at any time. This coverage is lower than the ~80% that is accessible by Hubble. The FOR, as is shown in Figure 74, allows one to observe targets from 85º to 135º of the Sun. Most astronomical targets are observable for two periods separated by 6 months during each year. The length of the observing window varies with ecliptic latitude, and targets within 5º of the ecliptic poles are visible continuously, and provides 100% accessibility of the sky during a year period. The sunshield permits the observatory to pitch toward and away from the sun by approximately 68º, while still keeping the telescope in the shade (Figure 75). The continuous viewing zone is important for some science programs that involve monitoring throughout the year and will also be useful for calibration purposes. Outside the continuous viewing zone every area in the sky is observable for at least 100 days per year. The maximum time on target at a given orientation is 10 days.
Figure 74: Schematic of observatory FOR (image credit: STScI, Ref. 36)
Figure 75: FOR directions of the OTE in relation to the Sun, Earth and Moon (red arrow), image credit: STScI
The sunshield has dimensions of about 20 m x 14 m providing ample shielding from light of the sun and the Earth. The sunshield provides a 5 layer, "V" groove radiator design of lightweight reflecting material. It reduces the 300 kW of radiation it receives from the sun on its sunward side, to a mere 23 mW (milliwatt) at the back, sufficient to sustain a 300 K temperature drop from front to back. With a back sunshield temperature of ~ 90 K, the primary mirror, the optical truss, and the instrument payload can radiate their heat to space (at 2.7 K) and reach cryogenic temperatures of 30-50 K. These low temperatures and the total blocking of direct or reflected sunlight are crucial to the scientific success of JWST. 122)
The five sunshield layers of ultra-thin membrane are constructed from DuPont Kapton® E. The first layer, at the hot side, is 50.8 µm thick. The remaining four layers are each 25.4 µm thick, similar in thickness to a human hair. The membranes use a vapor-deposited aluminum coating to produce a highly reflective surface and can sustain a 300 K temperature drop. Z-folded at launch, the sunshield will be signaled to begin deploying two days into launch, as the spacecraft heads toward its orbit. 123)
Figure 76: The five-layer finite element model of the JWST sunshield (image credit: NGAS)
Historically, membranes have been designed to induce a biaxial-tension stress state, thus guaranteeing that wrinkles do not form. The large-scale geometry of the JWST sunshield, along with its complex design features, may hinder such a biaxial stress state. Therefore, the ability to accurately predict the response of the membrane becomes critical to mission success. This article addresses the analytical problems involved in meeting those objectives and looks ahead to the challenges remaining in manufacturing the sunshield.
Figure 77: Overview of the JWST sunshield analysis process (image credit: NGAS)
Figure 78: Deployed observatory, back view: Spacecraft bus, solar arrays, communications antenna, and ISIM (image credit: NGAS)
| Total mass of spacecraft | ~ 6200 kg, including observatory, on-orbit consumables and launch vehicle adaptor |
| Mission duration | 5 years (10 year goal) |
| Diameter of primary mirror | 6.5 m |
| Clear aperture of primary mirror | 25 m2 |
| Primary mirror material | Beryllium |
| Mass of primary mirror | 705 kg |
| Mass of a single primary mirror segment | 20.1 kg for a single beryllium mirror, 39.48 kg for one entire PMSA (Primary Mirror Segment Assembly) |
| Focal length | 131.4 m |
| Number of primary mirror segments | 18 |
| Optical resolution | ~0.1 arcsecond |
| Wavelength coverage | 0.6 - 28 µm |
| Size of sunshield | 21.2 m x 14.2 m |
| Telescope operating temperature | ~45 K |
| Launch vehicle | Ariane 5 ECA (an ESA sponsored flight from Kourou) |
| Launch | 2021 |
Table 12: Overview of JWST mission parameters 124)
JWST continued
Development status of the JWST project
• November 5, 2021: After its arrival at Pariacabo harbor in French Guiana on 12 October 2021, the James Webb Space Telescope was transported to Europe's Spaceport and unboxed in the cleanroom. It is now being prepared for its launch on an Ariane 5 rocket in December. 125)
- Though the telescope weighs only six tons, it is more than 10.5 m high and almost 4.5 m wide when folded. It was shipped in its folded position in a 30 m long container which, with auxiliary equipment, weighed more than 70 tons.
Figure 79: After arriving in the harbor, the telescope inside its container was towed by a heavy-load tractor unit to the spacecraft processing facility at Europe's Spaceport. There, Webb's special shipping container was opened, and the telescope was unboxed inside the facility's cleanroom and installed on a rollover fixture to raise it vertical. This is how it will stand inside the Ariane 5 fairing (video credit: ESA/CNES/Arianespace/NASA's Goddard Space Flight Center)
- Webb's launch campaign involves more than 100 specialists. Teams will work separately to prepare the telescope and the launch vehicle until they become one combined team to join the telescope with its rocket for a momentous liftoff.
- Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, ESA is providing the telescope's launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace.
- Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
• November 2, 2021: Now that NASA's James Webb Space Telescope has safely arrived at its launch site in French Guiana, on the northeastern coast of South America, technical teams have begun making progress on the final checklist of preparations before liftoff later this year. 126)
- These preparations are expected to last 55 days from the observatory's arrival by ship to the day of launch.
- After Webb arrived at the Arianespace clean room facilities in French Guiana, contamination control technicians ensured the observatory is clean and contaminant free following its 5,800 mile journey. Then engineers ran a final set of electrical and functional tests and checked the stowed mechanical configuration to ensure delivery went smoothly. A trained crew in special hazmat suits will soon begin the two-week process of loading the spacecraft with the hydrazine fuel and nitrogen tetroxide oxidizer it will need to power its rocket thrusters to maintain its orbit. Next, Webb will move to the nearby vehicle integration building to be lifted and mounted on top of the Ariane 5 rocket "stack." The final few remove-before-flight "red-tag" items are taken off, and a few remaining add-before-flight "green tag" items are installed. Then the rocket fairing is lifted and lowered over top and locked into place, signifying the conclusion of a long journey. At this point, Webb will be very nearly ready to launch from Europe's Spaceport, also known as the Guiana Space Center (CSG).
Figure 80: Upon its arrival at the launch site in Kourou, French Guiana, engineers quickly set about unpacking, cleaning, and preparing the James Webb Space Telescope in its remaining days on Earth.
Credits: NASA/Chris Gunn)
- As a fully integrated launch vehicle with Webb as the payload, the Ariane rocket will roll out to the launch pad a few days before launch. Engineers monitor the rocket via electrical connections running from the payload control room to the pad through an umbilical attachment to the vehicle that separates at liftoff. A few hours before liftoff, the rocket is loaded with liquid hydrogen fuel and liquid oxygen oxidizer. About a half hour before launch, engineers in the payload control room switch the spacecraft from external electrical power to the spacecraft's on-board battery.
- Webb's launch will be a pivotal moment for NASA and its partners, ESA (European Space Agency) and the Canadian Space Agency (CSA), but it is only the beginning. The following 29 days will be an exciting but harrowing time. Thousands of parts must work correctly, in sequence, to unfold Webb and put it in its final configuration, all while it flies through the expanse of space alone, to a destination nearly one million miles away.
• October 18, 2021: The greatest origin story of all unfolds with the James Webb Space Telescope. Webb's launch is a pivotal moment that exemplifies the dedication, innovation, and ambition behind NASA and its partners, the European Space Agency (ESA) and Canadian Space Agency (CSA), but it is only the beginning. 127)
Figure 81: The 29 days following liftoff will be an exciting but harrowing time. Thousands of parts must work correctly, in sequence, to unfold Webb and put it in its final configuration, all while it flies through the expanse of space alone, to a destination nearly one million miles away. As the largest and most complex telescope ever sent into space, the James Webb Space Telescope is a technological marvel. By necessity, Webb takes on-orbit deployments to the extreme. Each step can be controlled expertly from the ground, giving Webb's Mission Operations Center full control to circumnavigate any unforeseen issues with deployment (video credit: NASA Goddard Space Flight Center)
• October 13, 2021: The James Webb Space Telescope arrived safely at Pariacabo harbor in French Guiana on 12 October 2021 ahead of its launch on an Ariane 5 rocket from Europe's Spaceport. 128)
Figure 82: Webb arrives in French Guiana for launch on Ariane 5 (image credit: ESA/CNES/Arianespace)
• October 12, 2021: The James Webb Space Telescope, a once in a generation space mission, arrived safely at Pariacabo harbor in French Guiana on 12 October 2021, ahead of its launch on an Ariane 5 rocket from Europe's Spaceport. 129)
- Webb, packed in a 30 m long container with additional equipment, arrived from California on board the MN Colibri which sailed the Panama Canal to French Guiana. The shallow Kourou river was specially dredged to ensure a clear passage and the vessel followed high tide to safely reach port.
- The MN Colibri, like its sister vessel the MN Toucan, were built to ship Ariane 5 rocket parts from Europe to French Guiana. They were specifically designed to carry a complete set of Ariane 5 parts across the Atlantic, while having a low enough draft to enable them to follow a route along the shallow Kourou river to the Pariacabo harbor.
- Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, ESA is providing the telescope's launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace.
- Few space science missions have been as eagerly anticipated as the James Webb Space Telescope (Webb). As the next great space science observatory following Hubble, Webb is designed to resolve unanswered questions about the Universe and see farther into our origins: from the formation of stars and planets to the birth of the first galaxies in the early Universe.
- Every launch requires meticulous planning and preparation. For Webb, this process began about 15 years ago. Its arrival at Pariacabo harbor is a major milestone in the Ariane 5 launch campaign.
- Though the telescope weighs only six tons, it is more than 10.5 m high and almost 4.5 m wide when folded. It was shipped in its folded position in a 30 m long container which, with auxiliary equipment, weighs more than 70 tons. This is such an exceptional mission that a heavy articulated vehicle was brought on board MN Colibri to carefully transport Webb to the Spaceport.
- The Spaceport's preparation facilities are ready for Webb's arrival. As extra protection from contamination, the clean rooms are fitted with additional walls of air filters and a dedicated curtain will shroud Webb after it is mounted on the rocket.
- This launch campaign involves more than 100 specialists. Teams will work separately to prepare the telescope and the launch vehicle until they become one combined team to join the telescope with its rocket for a momentous liftoff.
Figure 83: The James Webb Space Telescope has arrived safely at Pariacabo harbor in French Guiana on 12 October 2021 (image credit: ESA/CNES/Arianespace)
- When Webb arrives at the Spaceport, it will be unpacked inside a dedicated spacecraft preparation facility where it will be examined to ensure that it is undamaged from its voyage and in good working order.
- In parallel to Webb preparations, Ariane 5 rocket parts from Europe will come together in the launch vehicle integration building.
- Europe's powerful and highly reliable heavy-lift workhorse has an excellent track record spanning more than 100 launches and three decades. Ariane 5's ample fairing, 5.4 m diameter and 17 m high, provides enough space for Webb's folded spacecraft components, sunshield and mirrors.
- Ariane 5 is well suited for science satellites with proven capability to send missions to the second Lagrange Point (L2). Ariane 5 will release Webb directly on a path towards L2 on which it will continue for four weeks, eventually arriving at L2 which is four times farther away than the Moon is from Earth.
- A few customized features make Ariane 5 a perfect fit for Webb. These include the adaptation of venting ports at the base of the fairing which will be forced fully open during the flight. The fairing – the rocket's nose cone – will protect Webb from the acoustics at liftoff and during its journey through Earth's atmosphere. Its venting ports will enable extremely smooth depressurization of the fairing from ground pressure to vacuum during the flight.
- Then, to avoid overheating of any elements of Webb, Ariane 5 will perform a specially developed rolling maneuver to ensure that all parts of the satellite will be equally exposed to the sun.
- An extra battery will provide power for a boost to the upper stage after release of the telescope, safely distancing it from Webb.
• October 12, 2021: NASA's James Webb Space Telescope successfully arrived in French Guiana Tuesday, after a 16-day journey at sea. The 5,800-mile voyage took Webb from California through the Panama Canal to Port de Pariacabo on the Kourou River in French Guiana, on the northeastern coast of South America. 130)
- The world's largest and most complex space science observatory will now be driven to its launch site, Europe's Spaceport in Kourou, where it will begin two months of operational preparations before its launch on an Ariane 5 rocket, scheduled for Dec. 18.
- Once operational, Webb will reveal insights about all phases of cosmic history – back to just after the big bang – and will help search for signs of potential habitability among the thousands of exoplanets scientists have discovered in recent years. The mission is an international collaboration led by NASA, in partnership with the European and Canadian space agencies.
- "The James Webb Space Telescope is a colossal achievement, built to transform our view of the universe and deliver amazing science," said NASA Administrator Bill Nelson. "Webb will look back over 13 billion years to the light created just after the big bang, with the power to show humanity the farthest reaches of space that we have ever seen. We are now very close to unlocking mysteries of the cosmos, thanks to the skills and expertise of our phenomenal team."
- After completing testing in August at Northrop Grumman's Space Park in Redondo Beach, California, the Webb team spent nearly a month folding, stowing, and preparing the massive observatory for shipment to South America. Webb was shipped in a custom-built, environmentally controlled container.
- Late in the evening of Friday, Sept. 24, Webb traveled with a police escort 26 miles through the streets of Los Angeles, from Northrop Grumman's facility in Redondo Beach to Naval Weapons Station Seal Beach. There, it was loaded onto the MN Colibri, a French-flagged cargo ship that has previously transported satellites and spaceflight hardware to Kourou. The MN Colibri departed Seal Beach Sunday, Sept. 26 and entered the Panama Canal Tuesday, Oct. 5 on its way to Kourou.
- The ocean journey represented the final leg of Webb's long, earthbound travels over the years. The telescope was assembled at NASA's Goddard Space Flight Center in Greenbelt, Maryland, starting in 2013. In 2017, it was shipped to NASA's Johnson Space Center in Houston for cryogenic testing at the historic "Chamber A" test facility, famous for its use during the Apollo missions. In 2018, Webb shipped to Space Park in California, where for three years it underwent rigorous testing to ensure its readiness for operations in the environment of space.
- "A talented team across America, Canada, and Europe worked together to build this highly complex observatory. It's an incredible challenge – and very much worthwhile. We are going to see things in the universe beyond what we can even imagine today," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in Washington. "Now that Webb has arrived in Kourou, we're getting it ready for launch in December – and then we will watch in suspense over the next few weeks and months as we launch and ready the largest space telescope ever built."
Figure 84: After the custom-built shipping container carrying Webb is unloaded from the MN Colibri, Webb will be transported to its launch site, Europe's Spaceport in Kourou, French Guiana (image credit: NASA, Chris Gunn)
- After Webb is removed from its shipping container, engineers will run final checks on the observatory's condition. Webb will then be configured for flight, which includes loading the spacecraft with propellants, before Webb is mounted on top of the rocket and enclosed in the fairing for launch.
- "Webb's arrival at the launch site is a momentous occasion," said Gregory Robinson, Webb's program director at NASA Headquarters. "We are very excited to finally send the world's next great observatory into deep space. Webb has crossed the country and traveled by sea. Now it will take its ultimate journey by rocket one million miles from Earth, to capture stunning images of the first galaxies in the early universe that are certain to transform our understanding of our place in the cosmos."
• September 7, 2021: Major elements of the Ariane 5 rocket to launch the James Webb Space Telescope arrived safely in Kourou, French Guiana from Europe on 3 September 2021. 131)
Figure 85: The rocket's fairing, upper stage and core stage have been unloaded from the MN Toucan vessel at Pariacabo harbour and transported by special convoy to Europe's Spaceport about 3 km away from the wharf (image credit: ESA/CNES/Arianespace)
- Webb will be stowed folded inside the fairing built by RUAG Space in Emmen, Switzerland. This ogive-shaped fairing at the top of Ariane 5 is 5.4 m in diameter and over 17 m high. Made of carbon fibre-polymer composite, this structure will protect Webb from the thermal, acoustic, and aerodynamic stresses at liftoff on the ascent to space.
- Ariane 5's upper stage is built by ArianeGroup in Bremen, Germany. It gives Ariane 5 the flexibility to deploy scientific payloads to a highly precise second Lagrangian injection orbit. Its HM7B engine burns 14.7 t of liquid oxygen and liquid hydrogen propellant to deliver 6.6 t of thrust. It provides attitude control during the ascent and the separation of Webb. The Vehicle Equipment Bay, 'the brain', autonomously controls the whole vehicle and transmits all key flight parameters to the ground station network.
- The cryogenic core stage, built by ArianeGroup in France, is 5.4 m diameter and 30.5 m long and unfuelled weighs more than 14 tons. At liftoff, its Vulcain 2 engine burns 175 t of liquid oxygen and liquid hydrogen propellants to provide 140 t of thrust. It also provides roll control during the main propulsion phase.
- At Europe's Spaceport these Ariane 5 parts will be checked and prepared for assembly and integration before the mating of Webb on its top.
- Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, ESA is providing the telescope's launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace.
- Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
• August 26, 2021: The NASA/ESA/CSA James Webb Space Telescope has successfully completed its final tests and is being prepared for shipment to its launch site at Europe's Spaceport in French Guiana. 132)
- Tests were carried out at Northrop Grumman's facilities in California, USA, to ensure that the complex space science observatory will operate as designed when in space. Shipment operations have now begun, including all the necessary steps to prepare Webb for a safe journey through the Panama Canal to its launch location in French Guiana, on the northeastern coast of South America.
Figure 86: Fully assembled and fully tested, the NASA/ESA/CSA James Webb Space Telescope has completed its primary testing regimen and is soon preparing for shipment to its launch site at Europe's Spaceport in French Guiana. On this photo, Webb is folded as it will be for launch (image credit: NASA, Chris Gunn)
- Once Webb arrives at Europe's Spaceport, launch processing teams will prepare and configure the observatory for flight. This involves post-shipment checkouts and carefully loading the spacecraft's propellant tanks with fuel. Then, engineering teams will mate the observatory to its launch vehicle, an Ariane 5 rocket provided by ESA and make a 'dress rehearsal', before it rolls out to the launch pad two days before launch.
Figure 87: Webb launch timeline at Europe's Spaceport. Webb's flight into orbit will take place on an Ariane 5 rocket from Europe's Spaceport in French Guiana. As part of the international collaboration agreement, ESA is providing the observatory's launch service. - The Webb launch campaign of almost 70 days involves a team of more than 100 experts hosted at Europe's Spaceport. NASA is highly involved, working closely with ESA towards launch. - From liftoff until separation, CNES Launch Range services will track Ariane 5 from ground stations in Kourou, in Ascension Island (South Atlantic), Natal (Brazil), Libreville (Gabon) and Malindi (Kenya). - Immediately after Webb separates from the rocket, ESA's tracking station network, ESTRACK, will follow the Early Orbit Phase operations using its Malindi ground station in collaboration with NASA's station network (image credit: ESA)
- The James Webb Space Telescope is an amazing feat of human ingenuity – a mission with contributions from thousands of scientists, engineers, and other professionals from more than 14 countries and 29 states, in nine different time zones. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service. Besides that, ESA is contributing the NIRSpec instrument and a 50% share of the MIRI instrument, as well as personnel to support mission operations.
- "We are glad about the completion of all tests for Webb and thank all the teams for their excellent work. We are really excited that all the items necessary for the launch are now coming together at Europe's Spaceport," said Günther Hasinger, ESA Director of Science.
- After launch, Webb will undergo an action-packed six-month commissioning period. Moments after completing a 26-minute ride aboard the Ariane 5 launch vehicle, the spacecraft will separate from the rocket and its solar array will deploy automatically.
- Webb will take one month to fly to its intended orbital location in space nearly one million miles away from Earth at L2, slowly unfolding as it goes. Sunshield deployments will begin a few days after launch, and each step can be controlled expertly from the ground, giving Webb's launch full control to circumnavigate any unforeseen issues with deployment.
- Once the sunshield starts to deploy, the telescope and instruments will enter shade and start to cool over time. Over the ensuing weeks, the mission team will closely monitor the observatory's cooldown, managing it with heaters to control stresses on instruments and structures. In the meantime, the secondary mirror tripod will unfold, the primary mirror will unfold, Webb's instruments will slowly power up, and thruster firings will insert the observatory into a prescribed orbit.
Figure 88: During the first month in space, on its way to the second Lagrange point (L2), Webb will undergo a complex unfolding sequence. Key steps in this sequence are unfolding Webb's sunshield – a five-layer, diamond-shaped structure the size of a tennis court — and the iconic 6.5-meter wide mirror, consisting of a honeycomb-like pattern of 18 hexagonal, gold-coated mirror segments (image credit: ESA)
- Once the observatory has cooled down and stabilized at its frigid operating temperature, several months of alignments to its optics and calibrations of its scientific instruments will occur. Scientific operations are expected to commence approximately six months after launch.
- 'Flagship' missions like Webb are generational projects. Webb was built on both the legacy and the lessons of missions before it, such as the NASA/ESA Hubble Space Telescope, and it will in turn provide the foundation upon which future large astronomical space observatories may one day be developed.
- Webb is the next great space science observatory, designed to answer outstanding questions about the Universe and to make breakthrough discoveries in all fields of astronomy. Webb will see farther into our origins – from the formation of stars and planets, to the birth of the first galaxies in the early Universe.
• August 18, 2021: The upper stage of the Ariane 5 rocket which will launch the James Webb Space Telescope later this year, is on its way to Europe's Spaceport in French Guiana. 133)
- Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, ESA is providing the telescope's launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace.
- Overnight on 17 August 2021, Ariane 5's upper stage was transported in its container from ArianeGroup in Bremen to Neustadt port in Germany. Here it will board the MN Toucan vessel alongside other Ariane 5 elements to continue its journey to Kourou, French Guiana.
- The upper stage of Ariane 5 is manufactured by ArianeGroup, the prime contractor for the development and construction of the European family of Ariane 5 and Ariane 6 launch vehicles.
- Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
Figure 89: Ariane 5 upper stage for Webb heads for Europe's Spaceport (image credit: Ariane Group)
• May 11, 2021: For the last time while it is on Earth, the world's largest and most powerful space science telescope opened its iconic primary mirror. This event marked a key milestone in preparing the observatory for launch later this year. 134)
- As part of the NASA's James Webb Space Telescope's final tests, the 6.5 meter (21 feet 4 inch) mirror was commanded to fully expand and lock itself into place, just like it would in space. The conclusion of this test represents the team's final checkpoint in a long series of tests designed to ensure Webb's 18 hexagonal mirrors are prepared for a long journey in space, and a life of profound discovery. After this, all of Webb's many movable parts will have confirmed in testing that they can perform their intended operations after being exposed to the expected launch environment.
- "The primary mirror is a technological marvel. The lightweight mirrors, coatings, actuators and mechanisms, electronics and thermal blankets when fully deployed form a single precise mirror that is truly remarkable," said Lee Feinberg, optical telescope element manager for Webb at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "This is not just the final deployment test sequence that the team has pulled off to prepare Webb for a life in space, but it means when we finish, that the primary mirror will be locked in place for launch. It's humbling to think about the hundreds of dedicated people across the entire country who worked so hard to design and build the primary mirror, and now to know launch is so close."
- Making the testing conditions close to what Webb will experience in space helps to ensure the observatory is fully prepared for its science mission one million miles away from Earth.
- Commands to unlatch and deploy the side panels of the mirror were relayed from Webb's testing control room at Northrop Grumman, in Redondo Beach, California. The software instructions sent, and the mechanisms that operated are the same as those used in space. Special gravity offsetting equipment was attached to Webb to simulate the zero-gravity environment in which its complex mechanisms will operate. All of the final thermal blanketing and innovative shielding designed to protect its mirrors and instruments from interference were in place during testing.
- To observe objects in the distant cosmos, and to do science that's never been done before, Webb's mirror needs to be so large that it cannot fit inside any rocket available in its fully extended form. Like a piece of origami artwork, Webb contains many movable parts that have been specifically designed to fold themselves to a compact formation that is considerably smaller than when the observatory is fully deployed. This allows it to just barely fit inside a 16-foot (5-meter) rocket fairing, with little room to spare.
Figure 90: The conclusion of this test represents the team's final in a long series of checkpoints designed to ensure Webb's 18 hexagonal mirrors are prepared for a long life of profound discovery (image credit: NASA, Chris Gunn)
- To deploy, operate and bring its golden mirrors into focus requires 132 individual actuators and motors in addition to complex backend software to support it. A proper deployment in space is critically important to the process of fine-tuning Webb's individual mirrors into one functional and massive reflector. Once the wings are fully extended and in place, extremely precise actuators on the backside of the mirrors position and bend or flex each mirror into a specific prescription. Testing of each actuator and their expected movements was completed in a final functional test earlier this year.
Figure 91: This video shows the James Webb Space Telescope's mirrors during their long string of tests, from individual segments to the final tests of the assembled mirror [video credits: NASA's Goddard Space Flight Center Michael P. Menzel (AIMM): Producer Michael McClare (KBRwyle): Lead Videographer Sophia Roberts (AIMM): Videographer Michael P. Menzel (AIMM): Video Editor]
- "Pioneering space observatories like Webb only come to fruition when dedicated individuals work together to surmount the challenge of building something that has never been done before. I am especially proud of our teams that built Webb's mirrors, and the complex back-end electronics and software that will empower it to see deep into space with extreme precision. It has been very interesting, and extremely rewarding to see it all come together. The completion of this last test on its mirrors is especially exciting because of how close we are to launch later this year," said Ritva Keski-Kuha, deputy optical telescope element manager for Webb at Goddard.
- Following this test engineers will immediately move on to tackle Webb's final few tests, which include extending and then restowing two radiator assemblies that help the observatory cool down, and one full extension and restowing of its deployable tower.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• March 30, 2021: Mission officials for NASA's James Webb Space Telescope have announced the selection of the General Observer programs for the telescope's first year of science, known as Cycle 1. These specific programs will provide the worldwide astronomical community with one of the first extensive opportunities to investigate scientific targets with Webb. 135) 136)
- The General Observer scientific observations for the NASA/ESA/CSA James Webb Space Telescope's first year of operation have been selected. Proposals from ESA member states comprise 33% of the total number of selected proposals and correspond to 30% of the available telescope time on Webb.
- The 286 selected proposals address a wide variety of science areas and will help fulfill NASA's overarching mission to further our understanding of the universe and our place in it. Webb will begin observing the universe in 2022 after the spacecraft unfolds, travels a million miles, and checks the functioning of all of its instruments.
- "The initial year of Webb's observations will provide the first opportunity for a diverse range of scientists around the world to observe particular targets with NASA's next great space observatory," said Dr. Thomas Zurbuchen, Associate Administrator for the Science Mission Directorate at NASA. "The amazing science that will be shared with the global community will be audacious and profound."
- Webb's large mirror, near- to mid-infrared sensitivity, and high-resolution imaging and spectroscopic capabilities will reveal parts of the universe that have been hidden so far. General Observer programs selected in this cycle seek to find the first galaxies, explore the formation of stars, and measure physical and chemical properties of planetary systems, including our own solar system.
- "We are opening the infrared treasure chest, and surprises are guaranteed," said Dr. John C. Mather, Senior Project Scientist for the Webb mission and Senior Astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "How did the universe make galaxies, stars, black holes, and planets, and our own very special little Earth? I don't know yet, but we are getting closer every day."
- General Observer time with Webb is extremely competitive. As a result, the proposal selection process conducted by the Telescope Allocation Committee is both rigorous and meticulous. The committee was comprised of nearly 200 members of the worldwide astronomical community who were assigned to 19 different panels covering broad scientific topics. The panels met virtually, due to the ongoing COVID-19 pandemic circumstances, over the course of several weeks. Members additionally spent countless hours outside of formal meetings to assess proposals.
- Using dual-anonymous review, where the identities of the proposing investigator and team were concealed, the scientific merit of each proposal was evaluated and ranked. The final, ranked list of selected proposals was presented to the Space Telescope Science Institute's Director, Dr. Kenneth Sembach, for review and approval.
Figure 92: This artist's illustration displays the scientific capabilities of NASA's James Webb Space Telescope. Webb's large mirror, near- to mid-infrared sensitivity, and high-resolution imaging and spectroscopic capabilities will allow astronomers to search for the first galaxies, explore the formation of stars, and measure physical and chemical properties of planetary systems, including our own solar system [image credits: NASA, ESA, and A. Feild (STScI)]
- "The first observing cycle with a new observatory is always special, especially one as powerful and highly anticipated as Webb. We had an incredibly interesting couple of weeks of intense proposal reviews during which the reviewers did a great job of sorting through and ranking all the possible science cases proposed. I commend them for their hard work, especially under pandemic conditions," said Sembach. "I'm very pleased to be able to approve such a strong science program for the observatory. These observations are going to provide stunning views of the universe and lead us in new investigative directions that will set the stage for decades of research."
- More than 1,000 proposals were submitted by the November 24, 2020 deadline. Scientists hailing from 44 countries applied for a portion of the 6,000 observing hours available in Webb's first year, which represents about two-thirds of all Cycle 1 observing time.
- "We celebrate the very successful partnership between the European Space Agency and our colleagues at NASA and the Canadian Space Agency," said Prof. Günther Hasinger, Director of Science at the European Space Agency. "We look forward to the beautiful images and spectra and the amazing discoveries that Webb will make in this first year of observations."
- "The Canadian Space Agency is proud to join NASA and ESA on this fantastic exploration of the Universe and back in cosmic time. We're all really looking forward to seeing this next generation space telescope in action," said Dr. Sarah Gallagher, Science Advisor to the President of the Canadian Space Agency. "Excitement is building as we get closer to the launch of Webb. These new targets for Webb's first science are highly anticipated observations that promise to expand our view of the Universe and our place in it. Congratulations to the group of outstanding astronomers on their successes in this rigorous selection process."
- General Observer programs will take place alongside Director's Discretionary-Early Release Science (ERS) and Guaranteed Time Observation (GTO) programs. All of these observations begin after the telescope's commissioning period, which takes at least six months.
- The full list of General Observer programs is available at https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go.
- The Space Telescope Science Institute (STScI) in Baltimore will conduct Webb science operations and house Webb's mission operations center, which commands and controls the telescope. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• March 18, 2021: NASA's James Webb Space Telescope is making continued progress for a launch in October as engineers close out a series of technical issues with the spacecraft but deal with one new problem. 137)
- In a March 16 presentation during a meeting of NASA's Astrophysics Advisory Committee, Eric Smith, JWST program scientist, said engineers had either completed work on, or were in the process of wrapping up, several technical issues the program had been tracking in recent months, none of which posed a risk to the mission's schedule.
- Those issues included concerns about residual air pressure in the spacecraft's sunshield that could stress it when the Ariane 5 rocket that will launch JWST jettisons its payload fairing. Smith said that issue has been closed after adding a couple patches to the sunshield to ensure it could handle double the required pressure differential. Another issue, fasteners on the spacecraft that may not have been installed with sufficient torque, has also been resolved by retorquing those fasteners.
- The project has 48 days of schedule margin remaining, which Smith said was in line with projections at this phase of development. "We're burning it down at the pace expected," he said of that schedule margin.
- JWST is currently going through a final series of deployment tests, including of its primary mirror. The spacecraft will then be prepared for shipment later this summer to Kourou, French Guiana, for final launch preparations.
- Smith said the program is dealing with one new technical issue. Two communications transponders suffered separate problems during testing in January. Engineers have tracked down the problems with the two units and started repairs this week. "Those boxes will be back in time for us to make our planned shipping date," he said.
- That issue, he acknowledged, will use some of the remaining schedule margin. "The plan right now is that we'll get them back in time so that we don't have to use all of it," he said. "That's the main thing that we're watching regarding the margin."
- One other issue is the name of the spacecraft itself. The telescope is named after James Webb, the NASA administrator for much of the 1960s known for his leadership of the agency during the race to the moon. Earlier in his career, Webb worked at the State Department and reportedly oversaw policies there to purge the department of LGBT employees. Some object to the name for that reason and have called on NASA to rename the telescope.
- Smith said both NASA's chief historian, Brian Odom, and other historians outside the agency have been studying Webb's activities at the State Department. "They haven't completed their research in the archives yet, but when they do, that's when the agency would come out with a position on that," he said.
Roman delays
- While JWST is sticking to its October launch date, the next flagship astrophysics mission, the Nancy Grace Roman Space Telescope, is likely to be delayed because of a slowdown in activity during the pandemic.
- "We do have COVID impacts," said Julie McEnery, senior project scientist for the mission, previously known as the WFIRST (Wide Field Infrared Survey Telescope). In a presentation at the same meeting March 16, she said the program has been running at "70% efficiency" since the start of the pandemic a year ago, and would likely remain there for several more months as the pandemic slowly ebbs.
- "The delay is on the order of months, not years," she said, adding that the pandemic was the only issue the telescope was facing. "Fundamentally, Roman is on track. Except for the COVID-related impacts, everything is coming together and is where it needs to be."
- Speaking to the committee March 15, Paul Hertz, director of NASA's astrophysics division, said Roman's launch date would likely move from late 2025 to the middle of 2026 because of the pandemic. "It will need additional funding to pay for that schedule slip," he said, but didn't give an estimate of that increased cost since the agency is still reviewing estimates of the delay and related costs.
• March 8, 2021: On the occasion of International Women's Day 2021, and as excitement builds for the launch of the James Webb Space Telescope (Webb) in October, ESA is highlighting women that play an important role in Europe's contribution to Webb. 138)
- Webb, which is scheduled for launch on 31 October 2021, will be the next great space science observatory expected to make breakthrough discoveries in all fields of astronomy. It will look farther and deeper into the Universe than ever before: from our own Solar System, to exoplanets around other stars, and the birth of the first stars and galaxies.
- ESA is one of the partners in the international Webb mission alongside NASA and the Canadian Space Agency (CSA). Europe plays a crucial role by contributing to two instruments (NIRSpec and MIRI), and by launching the telescope on an Ariane 5 rocket from Europe's Spaceport in Kourou. ESA scientists are also supporting Webb mission operations at the Space Telescope Science Institute (STScI) in Baltimore, USA.
- On International Women's Day, which was first celebrated in four European countries in 1911, ESA joins in to honor women's achievements in making our upcoming space observatory a reality. We have asked women working on the Webb telescope about their challenges, their career highlights, what they're looking forward to about the Webb mission, and their advice to young people who might be considering careers in the space industry.
Figure 93: #WebbTelescopeWomen. On International Women's Day, ESA joins in to honor women's achievements in making the James Webb Space Telescope (Webb) a reality (image credit: ESA; NASA; Northrop Grumman; portraits supplied by contributors)
• March 1, 2021: February marked significant progress for NASA's James Webb Space Telescope, which completed its final functional performance tests at Northrop Grumman in Redondo Beach, California. Testing teams successfully completed two important milestones that confirmed the observatory's internal electronics are all functioning as intended, and that the spacecraft and its four scientific instruments can send and receive data properly through the same network they will use in space. These milestones move Webb closer to being ready to launch in October. 139)
- These tests are known as the comprehensive systems test, which took place at Northrop Grumman, and the ground segment test, which took place in collaboration with the STScI (Space Telescope Science Institute) in Baltimore.
- Before the launch environment test, technicians ran a full scan known as a comprehensive systems test. This assessment established a baseline of electrical functional performance for the entire observatory, and all of the many components that work together to comprise the world's premiere space science telescope. Once environmental testing concluded, technicians and engineers moved forward to run another comprehensive systems test and compared the data between the two. After thoroughly examining the data, the team confirmed that the observatory will both mechanically and electronically survive the rigors of launch.
- Through the course of 17 consecutive days of systems testing, technicians powered on all of Webb's various electrical components and cycled through their planned operations to ensure each was functioning and communicating with each other. All electrical boxes inside the telescope have an "A" and "B" side, which allows redundancy in flight and added flexibility. During the test all commands were input correctly, all telemetry received was correct and all electrical boxes, and each backup side functioned as designed.
- "It's been amazing to witness the level of expertise, commitment and collaboration across the team during this important milestone," said Jennifer Love-Pruitt, Northrop Grumman's electrical vehicle engineering lead on the Webb observatory. "It's definitely a proud moment because we demonstrated Webb's electrical readiness. The successful completion of this test also means we are ready to move forward toward launch and on-orbit operations."
Figure 94: During its final full systems test, technicians powered on all of the James Webb Space Telescope's various electrical components installed on the observatory, and cycled through their planned operations to ensure each was functioning, and communicating with each other. — Following the conclusion of the James Webb Space Telescope's recent milestone tests, engineering teams have confirmed that the observatory will both mechanically, and electronically survive the rigors anticipated during launch (image credit: NASA/Chris Gunn)
Webb's recent systems scan confirms the observatory will withstand the launch environment.
- Following the completion of Webb's final comprehensive systems evaluation, technicians immediately began preparations for its next big milestone, known as a ground segment test. This test was designed to simulate the complete process from planning science observations to posting the scientific data to the community archive.
- Webb's final ground segment test began by first creating a simulated plan that each of its scientific instruments would follow. Commands to sequentially turn on, move, and operate each of four scientific instruments were then relayed from Webb's Mission Operations Center (MOC) at the Space Telescope Science Institute (STScI) in Baltimore. During the test, the observatory is treated as if it were a million miles away in orbit. To do this, the Flight Operations Team connected the spacecraft to the Deep Space Network, an international array of giant radio antennas that NASA uses to communicate with many spacecraft. However, since Webb isn't in space yet, special equipment was used to emulate the real radio link that will exist between Webb and the Deep Space Network when Webb is in orbit. Commands were then relayed through the Deep Space Network emulator to the observatory at Northrop Grumman.
- One of the unique aspects of Webb's final ground segment test occurred during a simulated flight environment when the team successfully practiced seamlessly switching over control from its primary MOC at STScI in Baltimore to the backup MOC at NASA's Goddard Space Flight Center in Greenbelt, Maryland. This demonstrated a backup plan that isn't anticipated to be needed but is necessary to practice and perfect prior to launch. Additionally, team members successfully sent multiple software patches to the observatory while it was performing its commanded operations.
- "Working in a pandemic environment, of course, is a challenge, and our team has been doing an excellent job working through its nuances. That's a real positive to highlight, and it's not just for this test but all of the tests we've safely completed leading up to this one," said Bonnie Seaton, deputy ground segment & operations manager at Goddard. "This recent success is attributable to many months of preparation, the maturity of our systems, procedures, and products and the proficiency of our team."
- When Webb is in space, commands will flow from STScI to one of the three Deep Space Network locations: Goldstone, California; Madrid, Spain; or Canberra, Australia. Signals will then be sent to the orbiting observatory nearly one million miles away. Additionally, NASA's Tracking and Data Relay Satellite network – the Space Network in New Mexico, the European Space Agency's Malindi station in Kenya, and ESOC (European Space Operations Centre) in Germany – will help keep a constant line of communication open with Webb.
- Engineers and technicians continue to follow personal safety procedures in accordance with current CDC and Occupational Safety and Health Administration guidance related to COVID-19, including mask wearing and social distancing. The team is now preparing for the next series of technical milestones, which will include the final folding of the sunshield and deployment of the mirror, prior to shipment to the launch site.
- The next series of milestones for Webb include a final sunshield fold and a final mirror deployment.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• December 18, 2020: Lengthened to the size of a tennis court, the five-layer sunshield of NASA's fully assembled James Webb Space Telescope successfully completed a final series of large-scale deployment and tensioning tests. This milestone puts the observatory one step closer to its launch in 2021. 140)
- "This is one of Webb's biggest accomplishments in 2020," said Alphonso Stewart, Webb deployment systems lead for NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We were able to precisely synchronize the unfolding motion in a very slow and controlled fashion and maintain its critical kite-like shape, signifying it is ready to perform these actions in space."
- The sunshield protects the telescope and reflects light and background heat from the Sun, Earth and Moon into space. The observatory must be kept cold to accomplish groundbreaking science in infrared light, which is invisible to human eyes and felt as heat.
- In the sunshield's shadow, Webb's innovative technologies and sensitive infrared sensors will allow scientists to observe distant galaxies and study many other intriguing objects in the universe.
- Maintaining the sunshield's shape involves a delicate, complicated process.
- "Congratulations to the entire team. Due to Webb's large size and stringent performance requirements, the deployments are incredibly complex. In addition to the required technical expertise, this set of tests required detailed planning, determination, patience and open communication. The team proved that it has all these attributes. It's amazing to think that next time Webb's sunshield is deployed it will be many thousands of miles away, hurtling through space," said James Cooper, Webb's sunshield manager at Goddard.
- The Kapton® polymer-coated membranes of Webb's sunshield were fully deployed and tensioned in December at Northrop Grumman in Redondo Beach, California. Northrop Grumman designed the observatory's sunshield for NASA.
- During testing, engineers sent a series of commands to spacecraft hardware that activated 139 actuators, eight motors, and thousands of other components to unfold and stretch the five membranes of the sunshield into its final taut shape. A challenging part of the test is to unfold the sunshield in Earth's gravity environment, which causes friction, unlike unfolding material in space without the effects of gravity.
- For launch the sunshield will be folded up around two sides of the observatory and placed in an Ariane 5 launch vehicle, which is provided by the European Space Agency.
Figure 95: The James Webb Space Telescope's final tests are underway with the successful completion of its last sunshield deployment test, which occurred at Northrop Grumman in Redondo Beach, California (image credit: NASA/Chris Gunn)
- In this test, two pallet structures that hold the sunshield upright folded down, then two huge "arms" (known as the Mid-Boom Assembly) of the sunshield slowly telescoped outward, pulling the folded membranes along with them to resemble the synchronized movements of a very slowly choreographed dance. Once the arms locked in their horizontal position, the membranes of the sunshield were successfully tensioned individually starting with the bottom layer, separating each into their fully deployed shape.
- The large sunshield divides the observatory into a warm, Sun-facing side (about 185 degrees Fahrenheit) and a cold-space-facing side (minus 388 degrees Fahrenheit) comprised of the optics and scientific instruments. The sunshield will protect the observatory's optics and sensors, so they remain at extremely cold temperatures to conduct science.
- "This milestone signals that Webb is well on its way to being ready for launch. Our engineers and technicians achieved incredible testing progress this month, reducing significant risk to the project by completing these milestones for launch next year," said Bill Ochs, project manager for Webb at Goddard. "The team is now preparing for final post-environmental deployment testing on the observatory these next couple of months prior to shipping to the launch site next summer."
- Webb has passed other rigorous deployment tests during its development, which successfully uncovered and resolved technical issues with the spacecraft. These tests validate that once in orbit, the observatory and its many redundant systems will function flawlessly.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• August 24, 2020: Testing teams have successfully completed a critical milestone focused on demonstrating that NASA's James Webb Space Telescope will respond to commands once in space. - Known as a "Ground Segment Test," this is the first time commands to power on and test Webb's scientific instruments have been sent to the fully-assembled observatory from its Mission Operations Center at the Space Telescope Science Institute (STScI) in Baltimore, Maryland. 141)
- Since reliably communicating with Webb when in space is a mission-critical priority for NASA, tests like these are part of a comprehensive regimen designed to validate and ensure all components of the observatory will function in space with the complex communications networks involved in both sending commands, and downlinking scientific data. This test successfully demonstrated the complete end-to-end flow from planning the science Webb will perform to posting the scientific data to the community archive.
- "This was the first time we have done this with both the actual Webb flight hardware and the ground system. We've performed pieces of this test as the observatory was being assembled, but this is the first ever, and fully successful, end-to-end operation of the observatory and ground segment. This is a big milestone for the project, and very rewarding to see Webb working as expected," said Amanda Arvai, Deputy Division Head of Mission Operations at STScI in Maryland.
- In this test, commands to sequentially turn on, move, and operate each of Webb's four scientific instruments were relayed from the Mission Operations Center. During the test, the observatory is treated as if it were a million miles away in orbit. To do this, the Flight Operations Team connected the spacecraft to the Deep Space Network, an international array of giant radio antennas that NASA uses to communicate with many spacecraft. However, since Webb isn't in space yet, special equipment was used to emulate the real radio link that will exist between Webb and the Deep Space Network when Webb is in orbit. Commands were then relayed through the Deep Space Network emulator to the observatory, which is currently inside a Northrop Grumman clean room in Redondo Beach, California.
- "This was also the first time we've demonstrated the complete cycle for conducting observations with the observatory's science instruments. This cycle starts with the creation of an observation plan by the ground system which is uplinked to the observatory by the Flight Operations Team. Webb's science instruments then performed the observations and the data was transmitted back to the Mission Operations Center in Baltimore, where the science was processed and distributed to scientists," said Arvai.
- When Webb is in space, commands will flow from STScI in Baltimore to one of the three Deep Space Network locations —California, Spain, or Australia. Signals will then be sent to the orbiting observatory nearly one million miles away. Additionally the NASA's Tracking and Data Relay Satellite network, the Space Network in New Mexico, the European Space Agency's Malindi station in Kenya, and European Space Operations Centre in Germany will also aid in keeping a constant line of communication open with Webb at all times.
Figure 96: Inside Webb's Mission Operations Center, Test Operator Jessica Hart is seen on-console at the Space Telescope Science Institute in Baltimore, Maryland monitoring test progress with social distancing protocol in place (image credits: STSCI/Amanda Arvai)
- To complete the ground segment test a team of nearly 100 people worked together through the course of four consecutive days. Due to staffing restrictions in place due to the coronavirus (COVID-19) pandemic, only seven individuals were present inside the Mission Operations Center, with the rest working remotely to routinely monitor progress. Next up for Webb: observatory level acoustic and sine-vibration testing that will demonstrate that the assembled telescope is capable of surviving the rigors of launch by exposing it to similar conditions.
- Webb is NASA's next great space science observatory, which will help in solving the mysteries of our solar system, looking beyond to distant worlds around other stars, and probing the mystifying structures and origins of our universe. Webb is an international program led by NASA, along with its partners ESA (European Space Agency) and the Canadian Space Agency.
• June 9, 2020: To test the James Webb Space Telescope's readiness for its journey in space, technicians successfully commanded it to deploy and extend a critical part of the observatory known as the Deployable Tower Assembly. 142)
- The primary purpose of the deployable tower is to create a large gap between the upper part of the observatory that houses its iconic gold mirrors and scientific instruments, and the lower section known as the spacecraft bus which holds its comparatively warm electronics and propulsion systems. By creating a space between the two, it allows for Webb's active and passive cooling systems to bring its mirrors and sensors down to staggeringly cold temperatures required to perform optimal science.
- Webb was designed to look for faint traces of infrared light, which is essentially heat energy. To detect the extremely faint heat signals of astronomical objects that are incredibly far away, the telescope itself has to be very cold and stable.
- During the test, the tower was slowly extended 48 inches (1.2 meters) upward over the course of several hours, in the same maneuver it will perform once in space. Simulating the zero-gravity environment Webb will operate in, engineers employed an innovative series of pulleys, counterbalances and a special crane called a gravity-negation system that perfectly offloaded all of the effects of Earth's gravity on the observatory. Now that Webb is fully assembled, the difficulty of testing and properly simulating a zero-gravity environment has increased significantly.
- "The Deployable Tower Assembly worked beautifully during the test," said Alphonso Stewart the Webb deployment systems lead for NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It performed exactly as predicted, and from our expectations from previous tests before the full observatory was assembled. This was the first time that this part of Webb was tested in its flight-like configuration to the highest level of fidelity we possibly could. This test provides the opportunity to assess all interfaces and interactions between the instrument and bus sections of the observatory."
- In addition to helping the observatory cool down, the Deployable Tower Assembly is also a big part of how Webb is able to pack into a much smaller size to fit inside an Ariane 5 rocket for launch. Webb is the largest space science observatory ever built, but to fit a telescope that big into a rocket, engineers had to design it to fold down into a much smaller configuration. Webb's Deployable Tower Assembly helps Webb to just barely fit inside a 17.8-foot (5.4-meter) payload fairing. Once in space, the tower will extend to give the rest of Webb's deployable parts, such as the sunshield and mirrors, the necessary amount of room needed to unpack and unfold into a fully functional infrared space observatory.
- "We need to know that Webb will work the way we expect it to before we send it to space," said Stewart. "This is why we test, and when we do, we test as flight-like as possible. The way we send the commands to the spacecraft, the sequence, the individual sitting at the console, the communication that we use. We replicate all of these things to see if we are missing something, to see if there is something that needs to be changed, and to make sure that all of our planning to date has been correct."
Figure 97: To test the James Webb Space Telescope's readiness for its journey in space, technicians successfully commanded it to deploy and extend a critical part of the observatory known as the Deployable Tower Assembly. In this test, the deployable tower was commanded to extend 48 inches (1.2 meters) over the course of several hours to ensure that the observatory will be able to complete this process once in space (Producer, Videographer, Editor – Michael McClare (KBRwyle). Video credits: NASA Goddard Space Flight Center)
- Following augmented personal safety procedures due to COVID-19, the James Webb Space Telescope's Northrop Grumman team in California continued integration and testing work with significantly reduced on-site personnel and shifts. The NASA/Northrop Grumman team recently resumed near-full operations. NASA is evaluating potential impacts on the March 2021 launch date, and will continually assess the schedule and adjust decisions as the situation unfolds.
• May 14, 2020: NASA's James Webb Space Telescope has been successfully folded and stowed into the same configuration it will have when loaded onto an Ariane 5 rocket for launch next year. 143)
- Webb is NASA's largest and most complex space science telescope ever built. Too big for any rocket available in its fully expanded form, the entire observatory was designed to fold in on itself to achieve a much smaller configuration. Once in space, the observatory will unfold and stretch itself out in a carefully practiced series of steps before beginning to make groundbreaking observations of the cosmos.
- "The James Webb Space Telescope achieved another significant milestone with the entire observatory in its launch configuration for the first time, in preparation for environmental testing," said Bill Ochs, Webb project manager for NASA Goddard Space Flight Center in Greenbelt, Maryland. "I am very proud of the entire Northrop Grumman and NASA integration and test team. This accomplishment demonstrates the outstanding dedication and diligence of the team in such trying times due to COVID-19."
- The testing team's charter is to make sure every piece of hardware and every piece of software that comprise Webb will work not only individually, but as a full observatory. Now that Webb is completely assembled, technicians and engineers have seized the unique opportunity to command the entire spacecraft and carry out the various stages of movement and deployment it will perform when in space. By folding and stowing the spacecraft into the same configuration when it launches from French Guiana, the engineering team can confidently move forward with final environmental testing (acoustics and vibration). After completing the series of tests, Webb will be deployed one last time on Earth for testing prior to preparing for launch.
- "While operating under augmented personal safety measures because of the novel coronavirus (COVID-19), the project continues to make good progress and achieve significant milestones in preparation for upcoming environmental testing," said Gregory L. Robinson, the Webb program director at NASA Headquarters in Washington, D.C. "Team member safety continues to be our highest priority as the project takes precautions to protect Webb's hardware and continue with integration and testing. NASA will continually assess the project's schedule and adjust decisions as the situation evolves."
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Figure 98: A first look at NASA's James Webb Space Telescope fully stowed into the same configuration it will have when loaded into an Ariane V rocket for launch. The image was taken from a webcam in the clean room at Northrop Grumman, in Redondo Beach, California. With staffing restrictions in place due to COVID-19, only essential staff are allowed in the clean room (image credit: Northrop Grumman)
Figure 99: This video shows how NASA's James Webb Space Telescope is designed to fold to a much smaller size in order to fit inside the Ariane V rocket for launch to space. The largest, most complex space observatory ever built, must fold itself to fit within a 17.8 foot (5.4 m diameter) payload fairing, and survive the rigors of a rocket ride to orbit. After liftoff, the entire observatory will unfold in a carefully choreographed series of steps before beginning to make groundbreaking observations of the cosmos [video credit: Michael McClare (KBRwyle): Lead Producer, Bailee DesRocher (USRA): Lead Animator; (credits: NASA Goddard)]
Figure 100: For NASA's JWST to fit into an Ariane V rocket for launch, it must fold up. This graphic shows how Webb fits into the rocket fairing with little room to spare (image credit: Arianespace.com)
• March 31, 2020: In a recent test, NASA's James Webb Space Telescope fully deployed its primary mirror into the same configuration it will have when in space. 144)
- As Webb progresses towards liftoff in 2021, technicians and engineers have been diligently checking off a long list of final tests the observatory will undergo before being packaged for delivery to French Guiana for launch. Performed in early March, this procedure involved commanding the spacecraft's internal systems to fully extend and latch Webb's iconic 21 feet 4-inch (6.5 meter) primary mirror, appearing just like it would after it has been launched to orbit. The observatory is currently in a cleanroom at Northrop Grumman Space Systems in Redondo Beach, California.
Figure 101: Performed in early March, this most recent test involved commanding the spacecraft's internal systems to fully extend, and latch Webb's iconic 6.5 meter primary mirror into the same configuration it will have when in space (video credit: NASA, Sophia Roberts)
- The difficulty and complexity of performing tests for Webb has increased significantly, now that the observatory has been fully assembled. Special gravity offsetting equipment was attached to Webb's mirror to simulate the zero-gravity environment its mechanisms will have to operate in. Tests like these help safeguard mission success by physically demonstrating that the spacecraft is able to move and unfold as intended. The Webb team will deploy the observatory's primary mirror only once more on the ground, just before preparing it for delivery to the launch site.
- A telescope's sensitivity, or how much detail it can see, is directly related to the size of the mirror that collects light from the objects being observed. A larger surface area collects more light, just like a larger bucket collects more water in a rain shower than a small one. Webb's mirror is the biggest of its kind that NASA has ever built.
- In order to perform groundbreaking science, Webb's primary mirror needs to be so large that it cannot fit inside any rocket available in its fully extended form. Like the art of origami, Webb is a collection of movable parts employing applied material science that have been specifically designed to fold themselves to a compact formation that is considerably smaller than when the observatory is fully deployed. This allows it to just barely fit within a 5-meter payload fairing, with little room to spare.
- "Deploying both wings of the telescope while part of the fully assembled observatory is another significant milestone showing Webb will deploy properly in space. This is a great achievement and an inspiring image for the entire team," said Lee Feinberg, optical telescope element manager for Webb at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
- The evolving novel coronavirus COVID-19 situation is causing significant impact and disruption globally. Given these circumstances, Webb's Northrop Grumman team in California has resumed integration and testing work with reduced personnel and shifts until the Deployable Tower Assembly set up in April. The project will then shut down integration and testing operations due to the lack of required NASA onsite personnel related to the COVID-19 situation. The project will reassess over the next couple of weeks and adjust decisions as the situation continues to unfold.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• January 6, 2020: Researchers may have found a way that NASA's James Webb Space Telescope can quickly identify nearby planets that could be promising for our search for life, as well as worlds that are uninhabitable because their oceans have vaporized. 145)
Figure 102: Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. Crescents are other planets in the system, and the red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger (image credit: NASA/GSFC/Friedlander-Griswold)
- Since planets around other stars (exoplanets) are so far away, scientists cannot look for signs of life by visiting these distant worlds. Instead, they must use a cutting-edge telescope like Webb to see what's inside the atmospheres of exoplanets. One possible indication of life, or biosignature, is the presence of oxygen in an exoplanet's atmosphere. Oxygen is generated by life on Earth when organisms such as plants, algae and cyanobacteria use photosynthesis to convert sunlight into chemical energy.
- But what should Webb look for to determine if a planet has a lot of oxygen? In a new study, researchers identified a strong signal that oxygen molecules produce when they collide. Scientists say Webb has the potential to detect this signal in the atmospheres of exoplanets.
- "Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb, but we identify a promising way to detect it in nearby planetary systems," said Thomas Fauchez of the Universities Space Research Association at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "This oxygen signal is known since the early 80's from Earth's atmospheric studies, but has never been studied for exoplanet research." Fauchez is the lead author of the study, appearing in the journal Nature Astronomy January 6.
- The researchers used a computer model to simulate this oxygen signature by modeling the atmospheric conditions of an exoplanet around an M dwarf, the most common type of star in the universe. M dwarf stars are much smaller, cooler, and fainter than our Sun, yet much more active, with explosive activity that generates intense ultraviolet light. The team modelled the impact of this enhanced radiation on atmospheric chemistry, and used this to simulate how the component colors of the star's light would change when the planet would pass in front of it.
- As starlight passes through the exoplanet's atmosphere, the oxygen absorbs certain colors (wavelengths) of light— in this case, infrared light with a wavelength of 6.4 µm. When oxygen molecules collide with each other or with other molecules in the exoplanet's atmosphere, energy from the collision puts the oxygen molecule in a special state that temporarily allows it to absorb the infrared light. Infrared light is invisible to the human eye, but detectable using instruments attached to telescopes.
- "Similar oxygen signals exist at 1.06 and 1.27 m and have been discussed in previous studies but these are less strong and much more mitigated by the presence of clouds than the 6.4 µm signal," said Geronimo Villanueva, a co-author of the paper at Goddard.
- Intriguingly, oxygen can also make an exoplanet appear to host life when it does not, because it can accumulate in a planet's atmosphere without any life activity at all. For example, if the exoplanet is too close to its host star or receives too much star light, the atmosphere becomes very warm and saturated with water vapor from evaporating oceans. This water could be then broken down by the strong ultraviolet radiation into atomic hydrogen and oxygen. Hydrogen, which is a light atom, escapes to space very easily, leaving the oxygen behind.
- Over time, this process can cause entire oceans to be lost while building up a thick oxygen atmosphere. So, abundant oxygen in an exoplanet's atmosphere does not necessarily mean abundant life, but may instead indicate a rich water history.
- "Depending upon how easily Webb detects this 6.4 µm signal, we can get an idea about how likely it is that the planet is habitable," said Ravi Kopparapu, a co-author of the paper at Goddard. "If Webb points to a planet and detects this 6.4 µm signal with relative ease, this would mean that the planet has a very dense oxygen atmosphere and may be uninhabitable."
- The oxygen signal is so strong that it also can tell astronomers whether M dwarf planets have atmospheres at all, using just a few Webb transit observations.
- "This is important because M dwarf stars are highly active, and it has been postulated that stellar activity might 'blow away' entire planetary atmospheres," said Fauchez. "Knowing simply whether a planet orbiting an M dwarf can have an atmosphere at all is important for understanding star-planet interactions around these abundant but active stars."
- Although the oxygen signal is strong, cosmic distances are vast and M dwarfs are dim, so these stars will have to be relatively nearby for Webb to detect the signal in exoplanet atmospheres within a reasonable amount of time. An exoplanet with a modern Earth-like atmosphere will have to be orbiting an M dwarf that is within approximately 16 light-years of Earth. For a desiccated exoplanet with an oxygen atmosphere 22 times the pressure of Earth's, the signal could be detected up to about 82 light-years away. One light-year, the distance light travels in a year, is almost six trillion miles. For comparison, the closest stars to our Sun are found in the Alpha Centauri system a little over 4 light-years away, and our galaxy is about 100,000 light-years across.
- The research was funded in part by Goddard's Sellers Exoplanet Environments Collaboration (SEEC), which is funded in part by the NASA Planetary Science Division's Internal Scientist Funding Model. This project has also received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant, the NASA Astrobiology Institute Alternative Earths team, and the NExSS Virtual Planetary Laboratory.
- Webb will be the world's premier space science observatory, when it launches in 2021. It will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• August 28, 2019: Reaching a major milestone, engineers have successfully connected the two halves of NASA's James Webb Space Telescope for the first time at Northrop Grumman's facilities in Redondo Beach, California. Once it reaches space, NASA's most powerful and complex space telescope will explore the cosmos using infrared light, from planets and moons within our solar system to the most ancient and distant galaxies. 146)
- To combine both halves of Webb, engineers carefully lifted the telescope (which includes the mirrors and science instruments) above the already-combined sunshield and spacecraft using a crane. Team members slowly guided the telescope into place, ensuring that all primary points of contact were perfectly aligned and seated properly. The observatory has been mechanically connected; next steps will be to electrically connect the halves, and then test the electrical connections.
- "The assembly of the telescope and its scientific instruments, sunshield and the spacecraft into one observatory represents an incredible achievement by the entire Webb team," said Bill Ochs, Webb project manager for NASA Goddard Space Flight Center in Greenbelt, Maryland. "This milestone symbolizes the efforts of thousands of dedicated individuals for over more than 20 years across NASA, the European Space Agency, the Canadian Space Agency, Northrop Grumman, and the rest of our industrial and academic partners."
- Next up for Webb testing, engineers will fully deploy the intricate five-layer sunshield, which is designed to keep Webb's mirrors and scientific instruments cold by blocking infrared light from the Earth, Moon and Sun. The ability of the sunshield to deploy to its correct shape is critical to mission success.
- "This is an exciting time to now see all Webb's parts finally joined together into a single observatory for the very first time," said Gregory Robinson, the Webb program director at NASA Headquarters in Washington, D.C. "The engineering team has accomplished a huge step forward and soon we will be able to see incredible new views of our amazing universe."
- Both of the telescope's major components have been tested individually through all of the environments they would encounter during a rocket ride and orbiting mission a million miles away from Earth. Now that Webb is a fully assembled observatory, it will go through additional environmental and deployment testing to ensure mission success. The spacecraft is scheduled to launch in 2021.
- Webb will be the world's premier space science observatory. It will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency), and the Canadian Space Agency.
Figure 103: The fully assembled James Webb Space Telescope with its sunshield and unitized pallet structures (UPSs) that fold up around the telescope for launch, are seen partially deployed to an open configuration to enable telescope installation (image credit: NASA/Chris Gunn)
• August 6, 2019: In order to do groundbreaking science, NASA's James Webb Space Telescope must first perform an extremely choreographed series of deployments, extensions, and movements that bring the observatory to life shortly after launch. Too big to fit in any rocket available in its fully deployed form, Webb was engineered to intricately fold in on itself to achieve a much smaller size during transport. 147)
- Technicians and engineers recently tested a key part of this choreography by successfully commanding Webb to deploy the support structure that holds its secondary mirror in place. This is a critical milestone in preparing the observatory for its journey to orbit. The next time this will occur will be when Webb is in space, and on its way to gaze into the cosmos from a million miles away.
Figure 104: To ensure NASA's James Webb Space Telescope is prepared for liftoff, involved team members test critical parts of its deployment sequences on the ground. Recently Webb's secondary mirror and accompanying support structure were successfully fully deployed in the same configuration it will see when in space (video credit: NASA, Sophia Roberts)
- The secondary mirror is one of the most important pieces of equipment on the telescope, and is essential to the success of the mission. When deployed, this mirror will sit out in front of Webb's hexagonal primary mirrors, which form an iconic honeycomb-like shape. This smaller circular mirror serves an important role in collecting light from Webb's 18 primary mirrors into a focused beam. That beam is then sent down into the tertiary and fine steering mirrors, and finally to Webb's four powerful scientific instruments.
- "The proper deployment and positioning of its secondary mirror is what makes this a telescope – without it, Webb would not be able to perform the revolutionary science we expect it to achieve. This successful deployment test is another significant step towards completing the final observatory," said Lee Feinberg, optical telescope element manager for Webb at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
- Though there are many preparations still underway for the full assembly of the James Webb Space Telescope's two halves, the secondary mirror test represents the last large milestone before the integration of Webb into its final form as a complete observatory. This operation was also another demonstration that the electronic connection between the spacecraft and the telescope is working properly, and is capable of delivering commands throughout the observatory as designed.
- Webb will be the world's premier space science observatory. It will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Figure 105: Deployment test of Webb's secondary mirror. As one of the NASA Webb's most important components, technicians and engineers thoroughly inspect the support structure that holds its secondary mirror in place (visible in the top right corner of the image) following successful testing (image credit: NASA, Chris Gunn)
• February 8, 2019: NASA's James Webb Space Telescope has successfully passed another series of critical testing milestones on its march to the launch pad. In recent acoustic and sine vibration tests, technicians and engineers exposed Webb's spacecraft element to brutal dynamic mechanical environmental conditions to ensure it will endure the rigors of a rocket launch to space. 148)
Figure 106: NASA's James Webb Space Telescope has successfully passed another series of critical testing milestones on its march to the launch pad. In recent acoustic and sine vibration tests, technicians and engineers exposed Webb's spacecraft element to brutal dynamic mechanical environmental conditions to ensure it will endure the rigors of a rocket launch to space (video credit: NASA's Goddard Space Flight Center/Mike Menzel)
- During liftoff, rockets generate extremely powerful vibrations and energetic sound waves that bounce off the ground and nearby buildings and impact the rocket as it makes its way skyward. Technicians and engineers aim to protect Webb from these intense sound waves and vibrations.
- To simulate these conditions, flight components are intentionally punished with a long litany of tests throughout different facilities to identify potential issues on the ground. Webb was bombarded by powerful sound waves from massive speakers and then placed on an electrodynamic vibration table and strongly but precisely shaken. Together, these tests mimic the range of extreme shaking that spacecraft experience while riding a rocket to space.
- "Webb's launch vibration environment is similar to a pretty bumpy commercial airplane flight during turbulence," said Paul Geithner, deputy project manager – technical, James Webb Space Telescope at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "And, its launch acoustic environment is about 10 times more sound pressure, 100 times more intense and four times louder than a rock concert."
- One half of the Webb observatory, known as the "spacecraft element," was the subject of this latest testing. The spacecraft element consists of the "bus," which is the equipment that actually flies the observatory in space, plus the tennis-court-size sunshield that will keep Webb's sensitive optics and instruments at their required super-cold operating temperature. Northrop Grumman in Redondo Beach, California, NASA's lead industrial teammate on Webb, designed and built the spacecraft element, and conducted the testing in their facilities with NASA support and guidance. Northrop Grumman and NASA engineers and technicians worked tirelessly together as a team over the last few months to complete these complex dynamic mechanical environmental tests.
Figure 107: To keep Webb's spacecraft element and its sensitive instruments contaminant free, technicians and engineers enclose it in a protective clamshell that serves as a mobile clean room while in transport (image credit: NASA's Goddard Space Flight Center/Chris Gunn)
- The initial attempt at acoustic testing last spring uncovered a problem with a specific portion of sunshield hardware, which required some modifications taking several months. Subsequently, the acoustic test was redone, and this time everything went successfully. With acoustic testing complete, the spacecraft element was transported in a mobile clean room to a separate vibration facility, where its spacecraft hardware was exposed to the bumps and shakes that occur when riding a rocket soaring through the atmosphere at high Mach speeds. Northrop Grumman, NASA and its partner, ESA (European Space Agency), are familiar with the flight profile and performance of the Ariane 5 rocket that will carry Webb into space in early 2021, so technicians tuned the tests to mimic the conditions it's expected to face during launch.
- With the successful completion of its mechanical environmental testing, the spacecraft element is being prepared for thermal vacuum testing. This other major environmental test will ensure it functions electrically in the harsh temperatures and vacuum of space. The other half of Webb, which consists of the telescope and science instruments, had completed its own vibration and acoustic testing at Goddard and cryogenic-temperature thermal vacuum testing at NASA's Johnson Space Center in Houston prior to delivery at Northrop Grumman last year. Once finished with thermal vacuum testing, the spacecraft element will return to the giant clean room where it was assembled, to be deployed from its folded-up launch configuration and into its operational configuration, which will be the final proof that it has passed all of its environmental tests. Then, the two halves of Webb — the spacecraft and the telescope elements — will be integrated into one complete observatory for a final round of testing and evaluation prior to launch.
- Webb will be the world's premier space science observatory. It will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA and the Canadian Space Agency.
• September 26, 2018: For the first time, the two halves of NASA's James Webb Space Telescope — the spacecraft and the telescope—were connected together using temporary ground wiring that enabled them to "speak" to each other like they will in flight. 149)
- Although it was a significant step forward for the program, this test was an optional "risk reduction" test that took advantage of an opportunity to connect the two halves of the observatory together electrically months earlier than planned. If any issues had been found, it would have given engineers more time to fix them and without causing further delays. As a bonus, it also provided a jumpstart for the separate spacecraft and telescope test teams to begin working jointly as they will when the whole observatory is put together in one piece next year.
- The James Webb telescope is both an exceedingly complex and rewarding undertaking for NASA and its international partners. Scientists anticipate its findings to rewrite textbooks on astronomy by providing revolutionary observations of the cosmos, while engineers and involved technicians forecast that its challenging design will enable and influence future spacecraft architecture for years to come.
- Each piece of Webb has undergone rigorous testing throughout various historic and state of the art facilities across the United States. This ensures the entire observatory is prepared to survive the inherent harshness of a rocket launch to space, and years of continuous exposure to the extremes encountered on a mission nearly a million miles away from Earth.
- In February, Webb made an important, and symbolic step forward in its path to completion when all primary flight components of the observatory came to reside under the same roof at Northrop Grumman in Los Angeles, California. This is where all flight hardware is undergoing final assembly and testing until cleared to launch from the Guiana Space Centre near Kourou in French Guiana.
- "What we did now was make electrical connections between the flight telescope and flight spacecraft to understand all the nuances of the electrical interface. Specifically in this test, the spacecraft commanded mirror motion on the telescope, and the telescope replied back with telemetry confirming it. Even though we have tested each half with a simulator of the other half during their parallel construction, there is nothing exactly like connecting the real thing to the real thing. While the sunshield was being reassembled to get back into its environmental testing, we took advantage of the time and did a flight-to-flight electrical dry run right now to reduce schedule risk later," said Mike Menzel, Webb's Mission System Engineer. "The full complement of electrical and software tests will be run next year when the observatory is finally fully assembled for flight."
- The James Webb Space Telescope will be the world's premier space science observatory. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
Figure 108: With all flight components under one roof, technicians and engineers work to prepare the two halves of the James Webb Space Telescope for continued testing and eventual assembly in 2019 (image credit: Northrop Grumman)
• September 5, 2018: Success in JWST critical communications tests: When NASA's James Webb Space Telescope launches in 2021, it will write a new chapter in cosmic history. This premier space science observatory will seek the first stars and galaxies, explore distant planets around other stars, and solve mysteries of own solar system. Webb will be controlled from the MOC (Mission Operations Center) at the STScI (Space Telescope Science Institute) in Baltimore, Maryland. 150)
- To prepare for launch, the flight operations team recently conducted two successful communications tests. The first simulated the complex communications among numerous entities in the critical period of launch through the first six hours of flight. The second demonstrated that the MOC could successfully communicate with the telescope.
- A complicated dance: From the moment Webb launches, and through the first six hours of flight, five different telecommunications service providers located around the world will alternately convey command and telemetry data to the mission operations team in the MOC. The first exercise demonstrated the complex exchange among these facilities.
- These different providers are needed because of the geometry of Earth in relation to Webb's orbit and altitude. "Whereas most low-Earth missions can use TDRS (Tracking and Data Relay Satellite) or some other kind of communications satellite in orbit around Earth to relay data, we are so far away that we have to use other facilities," explained NASA's Carl Starr, the Mission Operations Manager for Webb at NASA's Goddard Space Flight Center, Greenbelt, Maryland.
- By six hours after liftoff, Webb will be about halfway to the Moon and six times higher in altitude than the geosynchronous Earth orbit (GEO) where TDRS and many communications satellites dwell. When the telescope reaches its destination, it will be 1.5 million km from Earth—about 45 times farther away than GEO.
- "It's a lot of going back and forth," said Starr. "You have to change configurations, you need a stable connection with Webb at each change, you have to establish the network connections, you have to process the data—and you have to do it multiple times with different stations and make it seamless."
- "And to make things even more complicated," Starr continued, "everyone we are talking about is in different places. You have the Space Network out in New Mexico, the DSN (Deep Space Network) in California, and the European Space Agency's Malindi station in Kenya and ESOC (European Space Operations Center) in Germany. It becomes a very complicated test to do, because no one is in the same time zone—and all of that data comes in and out of this building."
- This test was a major step in demonstrating the flight operations capabilities and processes to support launch-day communications. After the first day, the team moves to a normal setup with just the three DSN terminals around the world.
- "The teams were able to talk with the external entities, and prove the concept that we can manipulate the communications on the day of launch here in the building for the mission," Starr said. "We'll have other proficiency exercises later, but this was the first time that we did it, and it was very successful."
Figure 109: The Mission Operations Center for the James Webb Space Telescope is located at the STScI (Space Telescope Science Institute) in Baltimore, Maryland. In preparation for launch, the flight operations team recently conducted two critical and successful communications tests (image credit: STScI)
- Talking to the Telescope: No mission would be possible without communicating with the telescope. The flight operations team in Baltimore recently did that for the first time, talking to the actual Webb spacecraft on the ground while it's being integrated and tested across the country at the Northrop Grumman facility in Los Angeles, California.
- "We treated Webb as if it were a million miles away," said Starr. To do this, the flight operations team connected the spacecraft to the Deep Space Network. However, since Webb isn't really in space yet, special equipment was used to emulate the real radio link that will exist between Webb and the Deep Space Network when Webb flies. "We can command and control the vehicle now, and run tests with it from here, without having to travel to Northrop Grumman," Starr explained. "It really is making use of technology to stay on schedule."
- It didn't really matter where Webb was during the test. "As far as we're concerned, it could be in the basement of this building, and we wouldn't know any different," Starr added. "You're just at your console, you've got a data line, your screen ...it's all very much remote. I could imagine it must be how drone pilots feel. They're not anywhere near where their vehicle is."
- During the exercise, the team executed non-operational commands and initiated a recorder playback. This important test demonstrated the flight operations team's ability to command Webb from the MOC in Baltimore.
- Throughout most of commissioning, the MOC will be in constant communication with Webb. After commissioning, approximately 180 days after launch, the team will communicate for 8 hours a day with the telescope. During that time, operators will send up packages of commands for the telescope to run autonomously and downlink the science data.
- More to come: More tests will follow, but these were the first to show the MOC's successful communication with Webb and with the many command and telemetry service providers. The fact that these exercises were carried out flawlessly is a testament to the hard work of the flight operations team, as well as teams across the country and around the world.
- The JWST will be the world's premier space science observatory. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
• July 18, 2018: The sound associated with a rocket launch creates extreme vibrations that can adversely affect any satellite or observatory, so engineers put spacecraft through simulations to ensure they will remain operational. 151)
- The sunshield separates the observatory into a hot, sun-facing side (reaching temperatures close to 110º C), and a cold side (approximately -240ºC) where the sunlight is blocked from interfering with the sensitive telescope instruments.
- The James Webb Space Telescope will be the world's premier space science observatory. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
Figure 110: In this photo, technicians delicately inspect stowed sunshield membranes of NASA's JWST on the forward side of the spacecraft. Acoustic testing exposes the spacecraft to similar forces and stress experienced during liftoff, allowing engineers to better prepare it for the rigors of spaceflight (image credit: Northrop Grumman)
• June 5, 2018: How will NASA's James Webb Space Telescope shed the heat generated by its science instruments and their supporting electronics? To anyone who is not an engineer or scientist, the answer might be complex and "baffling," and it turns out the process is exactly that. 152)
- Webb's four science instruments are held within a support structure called the integrated science instrument module (ISIM), located behind the telescope's primary mirror. The ISIM and Webb's optics form the science payload of the observatory. To keep heat away from the sensitive instruments, a majority of the electronics used to power and operate the instruments are housed in a compartment below ISIM, where specially designed baffles direct the heat safely into space and away from any cold surfaces of the observatory.
- The baffles essentially act as mirrors to reflect the heat (infrared radiation) outward in a specific direction. If that sounds familiar, it is because Webb's mirrors will do very much the same thing — but instead of reflecting the infrared light into space, they will guide it with pinpoint accuracy to the telescope's science instruments.
- "Gold has a very high reflectivity in the infrared spectrum range, so it is ideal for directing heat," explained Matthew Stephens, a mechanical systems engineer for Webb at NASA's Goddard Space Flight Center in Greenbelt, MD. "This is the same reason all of the primary, secondary, and tertiary mirrors are gold-coated."
- The engineers in this photo of Figure 111 are reinstalling the baffles, which had been previously removed and safely stored in a clean environment to protect them from any contamination during integration and testing of the science payload. The clear plastic sheets placed over the baffles will protect them from any contamination during the remaining integration and testing phases for the observatory.
- The engineers had to reinstall the baffles before Webb's science payload and its spacecraft element (the combined spacecraft bus and sunshield) are integrated at Northrop Grumman Aerospace Systems in Redondo Beach, California, where both halves of the observatory currently reside. If the engineers wait until after integration, Webb's tennis-court-sized sunshield will obstruct the ISIM electronics compartment and make reinstalling the baffles much more difficult.
Figure 111: Engineers reinstall one of the gold-plated baffles that helps direct heat away from the integrated science instrument module (ISIM) of NASA's James Webb Space Telescope. The baffles direct the heat generated by the instrument electronics safely into space and away from any cold areas of the infrared telescope image credit: NASA/Chris Gunn)
Figure 112: Engineers carefully hold onto a gold-plated baffle as they use a scissor lift to access the back of the integrated science instrument module (ISIM) of NASA's James Webb Space Telescope. They are in the process of reinstalling the baffles, which direct the heat generated by the instrument electronics safely into space and away from any cold areas of the infrared telescope (image credit: NASA/Chris Gunn)
• June 4, 2018: In the last year, the James Webb Space Telescope (JWST) and in particular the telescope and the instruments have passed some key milestones on their road towards launch, now planned for 2020. 153)
- The first landmark was the completion of four-month long cryogenic tests in the giant thermal vacuum chamber, known as Chamber A, at NASA's Johnson Space Center in Houston, Texas. There, JWST's optical telescope and integrated science instrument module (OTIS) underwent a series of tests designed to check that the telescope and its four scientific instruments functioned as expected in an extremely cold, airless environment, similar to the conditions they will experience in space.
- On 27 September 2017, after confirming that OTIS can survive and operate flawlessly in temperatures of approximately 40 Kelvin (-233º C), engineers began to gradually warm the chamber. This was a very precise operation that required extreme caution in order to avoid contaminating the optical equipment or generating mechanical stresses that could damage the instruments or other JWST hardware.
- Once the thermal conditions inside the chamber returned to near room temperature, a final set of functional tests was performed under vacuum conditions. These tests confirmed that the warm-up procedure and OTIS cold testing had not caused any issue with respect to the functionality of the instruments and telescope. After this, the vacuum was slowly counteracted by pumping extra-clean air back into the chamber.
- The 40-ton chamber door was unsealed on 18 November 2017, marking the successful completion of the cryogenic testing, and OTIS finally emerged from Chamber A on 1 December, after some 100 days shut inside the cavernous vault.
Figure 113: The JWST's optical telescope and integrated science instrument module (OTIS) was removed from Chamber A at NASA's Johnson Space Center in Houston on 1 December 2017 (image credit: NASA/Chris Gunn)
A closer look at NIRSpec microshutters and detectors:
- After analysis of the data collected during the OTIS cryogenic test campaign, the team responsible for the European NIRSpec (Near InfraRed Spectrograph) confirmed that the instrument had operated very well and that its performance had not been impacted negatively, despite the intensive OTIS test campaign.
- The NIRSpec team was particularly pleased that the instrument's MSA (Micro Shutter Assembly), which comprises approximately 250,000 minuscule 'doors' that enable its Multi-Object Spectrograph capabilities, was in good health, having survived the earlier severe vibration and acoustic testing of OTIS. The performance of the microshutters, which are extremely delicate and can be susceptible to the strong acoustic stresses, could only be verified fully in cryogenic conditions.
Figure 114: Left: The NIRSpec instrument micro shutters – front view. Right: The NIRSpec instrument micro shutters – rear view (image credit: NASA)
- During testing, ESA scientists also commanded the instrument to mimic scientific operations in space and acquired samples of data to verify the spectrograph performance. The testing of OTIS demonstrated that the NIRSpec optics are very stable and ready to withstand the harsh conditions of launch.
- As for the detectors, their performance was confirmed to be "exquisite". Calibration images were acquired during OTIS testing while operating in NIRSpec MOS (Multi-Object Spectrographic) mode, which will allow astronomers to obtain spectra of more than 100 sources simultaneously. A typical calibration image shows many spectra recorded by the NIRSpec detectors and obtained by commanding selected microshutters open, with illumination provided using one of the instrument's internal calibration lamps.
- The calibration image of Figure 115 was acquired during testing of the NIRSpec instrument. NIRSpec will be used to study astronomical objects focussing on very distant galaxies. It will do so by splitting their light into spectra – separating the light into components allows scientists to investigate what these objects are made of.
Figure 115: This abstract image is a preview of the instrumental power that will be unleashed once the NASA/ESA/CSA James Webb Space Telescope will be in space (image credit: ESA/SOT team)
- Created using one of the instrument's internal calibration lamps as the light source, the image shows many spectra as horizontal bands that were recorded by two detectors,. The wavelengths are spread from left to right; the pattern of dark stripes, called absorption lines, is characteristic of the light source, much like a fingerprint.
- The image was produced by sending commands to open over 100 of the instrument's micro-shutters – minuscule windows the width of a human hair – that will be used to study hundreds of celestial objects simultaneously. The thin strips in the upper and lower parts of the image are spectra created by light that passed through the micro-shutters, while the thicker bands at the center of the images were produced by light that enters the instrument through five slits at the center.
- Once in space, the micro-shutters will be opened or closed depending on the distribution of stars and galaxies in the sky.
- This calibration image was obtained in 2017 during testing in the giant thermal vacuum chamber at NASA's Johnson Space Center in Houston, Texas. The tests demonstrated that the combined structure, comprising the Webb telescope and its four science instruments, operated flawlessly at temperatures of around –233°C, similar to those they will experience in space.
- The telescope and instruments are now at Northrop Grumman Aerospace Systems in Redondo Beach, California, where they will be integrated with the spacecraft and sunshield for further tests and launch preparations.
OTIS in the spotlight
- During the OTIS test campaign, the telescope and the instrument module were tested together at their operating temperature for the first time. To take advantage of that, a long suite of tests was performed using dedicated light sources that were temporarily mounted on OTIS.
- These sources, called ASPA (Aft Optical System Plate Assembly) optical stimuli, are used to send a variety of light beams onto the telescope and instrument optics in order to perform true end-to-end testing of the full JWST optical system, something that had not been done before.
- The resulting images and spectra obtained using all four of the Webb's instruments matched remarkably well with the expectations from computer simulations that had been performed several years prior to the actual OTIS test campaign.
- Another set of entirely different measurements also took place in the chamber to assess the stability of the OTIS hardware. Three very high-resolution camera systems, equipped with specially designed flash lamps and mounted on gigantic 3.4 meter-long rotating booms, were used to take multiple photographs of OTIS, tracking the position of hundreds of little reflective targets installed on the OTIS hardware.
Figure 116: The OTIS undergoing cryogenic testing inside Chamber A at NASA's Johnson Space Center in September 2017. A photogrammetry camera was placed inside the chamber to measure the telescope's alignment and to monitor the effect of extremely cold temperature on the black Kapton® material that is fitted to block unwanted light from behind the telescope. Also visible are the hexagonal primary mirror segments. The bright "stars" shining in this long-exposure photograph are photogrammetry targets that were used to measure extremely precise movements of the telescope as it cooled (image credit: NASA/Chris Gunn)
- The photogrammetry technique was instrumental to measure the miniscule movements and shrinkage of the hardware during the cool down. By doing so, engineers were able to measure positions with an accuracy of only a few tens of µm across the full extent of OTIS, which spans several meters.
- Finally a set of tests was conducted to check that a particular optical path, known as the "rogue path", was blocked. Unlike the NASA/ESA Hubble Space Telescope, which is equipped with a tube, JWST has an open, tubeless telescope design, so extra effort has to be spent to make sure that stray light cannot reach its detectors.
- This check was conducted using a third set of special light sources, consisting of arrays of LEDs arranged around the perimeter of the primary mirror. The procedure confirmed that this stray light path is properly blocked.
- After the warm-up inside Chamber A was completed, the actuators for the telescope's primary mirror segment were functionally tested before all 18 of the mirror segments were stowed. This cleared the way for the transportation of OTIS from Houston to Northrop Grumman Aerospace Systems in Redondo Beach, California, at the beginning of 2018 (Ref. 153).
• February 05, 2018: The two halves of NASA's James Webb Space Telescope now reside at Northrop Grumman Aerospace Systems in Redondo Beach, California, where they will come together to form the complete observatory. 154)
- Webb's OTIS (Optical Telescope and Integrated Science) instrument module arrived at Northrop Grumman Feb. 2, from NASA's Johnson Space Center in Houston, where it successfully completed cryogenic testing.
- "This is a major milestone," said Eric Smith, director of the James Webb Space Telescope Program at NASA. "The Webb observatory, which is the work of thousands of scientists and engineers across the globe, will be carefully tested to ensure it is ready to launch and enable scientists to seek the first luminous objects in the universe and search for signs of habitable planets."
- In preparation for leaving Johnson, OTIS was placed inside a specially designed shipping container called the Space Telescope Transporter for Air, Road and Sea (STTARS). The container then was loaded onto a U.S. military C-5 Charlie aircraft at Ellington Field Joint Reserve Base, just outside of Johnson. From there, OTIS took a flight to Los Angeles International Airport. After arrival, OTIS was driven from the airport to Northrop Grumman's Space Park facility (Figure 117).
- "It's exciting to have both halves of the Webb observatory – OTIS and the integrated spacecraft element – here at our campus," said Scott Willoughby, vice president and program manager for Webb at Northrop Grumman. "The team will begin the final stages of integration of the world's largest space telescope."
- During this summer, OTIS will combined with the spacecraft element to form the complete Webb observatory. Once the telescope is fully integrated, the entire observatory will undergo more tests during what is called observatory-level testing. Webb is scheduled to launch from Kourou, French Guiana, in 2019.
Figure 117: Photo of the STTARS (Space Telescope for Air, Road, and Sea) container with OTIS inside during unloading from the C-5 Charlie military aircraft at LAX (Los Angeles International Airport) on 2 Feb. 2018 (image credit: NASA, Chris Gunn)
Legend to Figure 117: STTARS is a massive container, measuring 4.6 m wide, 5.2 m toll, and 33.5 m long with a mass of 75,000 kg. It's much larger than the James Webb itself, but even then, the primary mirror wings and the secondary mirror tripod must be folded into flight configuration in order to fit.
• November 13, 2017: Following the recommendation of the Time Allocation Committee and a thorough technical review, the STScI (Space Telescope Science Institute) Director Ken Sembach has selected 13 science programs for the JWST Director's DD-ERS (Discretionary Early Release Science Program). It is anticipated that the DD-ERS observations will take place during the first 5 months of JWST science operations, following the 6-month commissioning period. 155) 156)
- With a total award of 460 hours of JWST observing time, the selected programs span a wide range of science areas as well as instrument modes, such as surveys of galaxies and their nuclei, stellar clusters and star formation near and far, the chemistry of interstellar and circumstellar matter, and the characterization of exoplanets. The successful programs include 16 Principal investigators (PIs) and co-PIs from North America and 6 from Europe, with broad world-wide participation.
1) The selected programs represent participation by 253 investigators from 18 countries, 22 U.S. states, and 106 unique institutions.
2) Of the 253 investigators, 157 are based in the U.S., 84 are from ESA countries, 7 are from Canada, and 5 are from other countries (Australia and Chile), with 248 unique investigators.
3) There are an additional 456 science collaborators involved in the programs.
4) The three largest teams have combined totals of 138, 105, and 80 investigators and collaborators.
The successful DD-ERS teams are now tasked with developing "science-enabling products," such as documentation for their programs, scientific software, and data products — all designed to help the full astronomical community maximize the science output of the JWST mission.
| ID | ERS Program | PI & Co-PIs | Category | Instruments |
| 1324 | Through the Looking GLASS: A JWST | PI: Tommaso Treu (University of | Galaxies and the IGM | NIRCam |
| 1345 | The Cosmic Evolution Early Release Science | PI: Steven Finkelstein (University of Texas at Austin) | Galaxies and the IGM | MIRI |
| 1386 | High Contrast Imaging of Exoplanets and | PI: Sasha Hinkley (University of Exeter) | Planets and Planet | MIRI |
| 1366 | The Transiting Exoplanet Community Early | PI: Natalie Batalha (NASA Ames Research Center) | Planets and Planet | MIRI |
| 1364 | Nuclear Dynamics of a Nearby Seyfert with | PI: Misty Bentz (Georgia State University | Massive Black Holes | NIRSpec |
| 1309 | IceAge: Chemical Evolution of Ices during | PI: Melissa McClure (Universiteit van Amsterdam) | Stellar Physics | MIRI |
| 1328 | A JWST Study of the Starburst-AGN | PI: Lee Armus (California Institute of Technology) | Galaxies and the IGM | MIRI |
| 1355 | TEMPLATES: Targeting Extremely Magnified | PI: Jane Rigby (NASA/GSFC | Galaxies and the IGM | MIRI |
| 1373 | ERS observations of the Jovian System as a | PI: Imke de Pater (University of California | Solar System | MIRI |
| 1335 | Q-3D: Imaging Spectroscopy of Quasar Hosts | PI: Dominika Wylezalek (European Southern | Massive Black Holes | MIRI |
| 1334 | The Resolved Stellar Populations Early Release | PI: Daniel Weisz (University of California | Stellar Populations | MIRI |
| 1349 | Establishing Extreme Dynamic Range with JWST: | PI: Ryan Lau (California Institute of Technology) | Stellar Physics | MIRI |
| 1288 | Radiative Feedback from Massive Stars as Traced | PI: Olivier Berne (Universite Toulouse) | Stellar Physics | MIRI |
Table 13: List of investigations in the DD-ERS Program
Figure 118: Once deployed, the JWST will conduct a variety of science missions aimed at improving our understanding of the Universe (image credit: NASA/STScI)
• October 19, 2017: What appears to be a unique selfie opportunity was actually a critical photo for the cryogenic testing of NASA's James Webb Space Telescope in Chamber A at NASA/JSC (Johnson Space Center) in Houston. The photo (Figure 119) was used to verify the line of sight (the path light will travel) for the testing configuration. 157)
- During Webb's extensive cryogenic testing, engineers checked the alignment of all the telescope optics and demonstrated the individual primary mirror segments can be properly aligned to each other and to the rest of the system. This all occurred in test conditions that simulated the space environment where Webb will operate, and where it will collect data of never-before-observed portions of the universe. Verifying the optics as a system is a very important step that will ensure the telescope will work correctly in space.
- The actual test of the optics involved a piece of support equipment called the ASPA (AOS Source Plate Assembly). The ASPA is a piece of hardware that sits atop Webb's AOS (Aft Optics Subsystem), which is recognizable as a black "nose cone" that protrudes from the center of Webb's primary mirror. The AOS contains the telescope's tertiary and fine-steering mirrors. The ASPA is ground test hardware, and it will be removed from the telescope before it is launched into space.
- During testing, the ASPA fed laser light of various infrared wavelengths into and out of the telescope, thus acting like a source of artificial stars. In the first part of the optical test, called the "half-pass" test, the ASPA fed laser light straight into the AOS, where it was directed by the tertiary and fine-steering mirrors to Webb's science instruments, which sit in a compartment directly behind the giant primary mirror. This test let engineers make measurements of the optics inside the AOS, and how the optics interacted with the science instruments. Critically, the test verified the tertiary mirror, which is immovable, was correctly aligned to the instruments.
- In another part of the test, called the "pass-and-a-half" test, light traveled in a reverse path through the telescope optics. The light was again fed into the system from the ASPA, but upwards, to the secondary mirror. The secondary mirror then reflected the light down to the primary mirror, which sent it back up to the top of Chamber A. Mirrors at the top of the chamber sent the light back down again, where it followed its normal path through the telescope to the instruments. This verified not only the alignment of the primary mirror itself but also the alignment of the whole telescope — the primary mirror, secondary mirror, and the tertiary and fine-steering mirrors inside the AOS.
- Taken together, the half-pass and pass-and-a-half tests demonstrated all the telescope optics are properly aligned and that they can be aligned again after being deployed in space.
Figure 119: Ball Aerospace optical engineer Larkin Carey is reflected in the James Webb Space Telescope's secondary mirror, as he photographs the line of sight for hardware used during an important test of the telescope's optics image credit: Ball Aerospace)
- The photo, snapped by Ball Aerospace optical engineer Larkin Carey after the final fiber optic connections between ASPA and the laser source outside the chamber were made, verified the line of sight for the pass-and-a-half part of the test. The image was compared with one collected once the telescope was cold inside the chamber, to ensure any observed obscurations were due to the ASPA hardware and would not be present during science data collection on orbit.
- In the photo, Carey is harnessed to a "diving board" over the primary mirror. All tools (including the camera) were tethered, and all safety protocol for working over the mirror were closely followed. Carey faced upwards and took the photo of the secondary mirror to verify the ASPA line of sight. The secondary mirror is reflecting him as well as the AOS, the ASPA, and the primary mirror below.
- "Intricate equipment is required to test an instrument as complex as the Webb telescope. The ASPA allowed us to directly test key alignments to ensure the telescope is working as we expect, but its location meant we had to have a person install over 100 fiber optic cables by hand over the primary mirror," said Allison Barto, Webb telescope program manager at Ball Aerospace. "This challenging task, which Larkin rehearsed many times to ensure it could be performed safely, also offered the opportunity to check the alignments by taking this 'selfie' prior to entering the test."
- After cryogenic testing at Johnson is complete, Webb's combined science instruments and optics journey to Northrop Grumman in Redondo Beach, California, where they will be integrated with the spacecraft element, which is the combined sunshield and spacecraft bus. Together, the pieces form the complete James Webb Space Telescope observatory. Once fully integrated, the entire observatory will undergo more tests during what is called "observatory-level testing." This testing is the last exposure to a simulated launch environment before flight and deployment testing on the whole observatory.
- Webb is expected to launch from Kourou, French Guiana, in the spring of 2019.
• August 24, 2017: NASA's James Webb Space Telescope will use its infrared capabilities to study the "ocean worlds" of Jupiter's moon Europa and Saturn's moon Enceladus, adding to observations previously made by NASA's Galileo and Cassini orbiters. The Webb telescope's observations could also help guide future missions to the icy moons. 158)
- Europa (Galilean moon of Jupiter) and Enceladus (moon of Saturn)are on the Webb telescope's list of targets chosen by guaranteed time observers, scientists who helped develop the telescope and thus get to be among the first to use it to observe the universe. One of the telescope's science goals is to study planets that could help shed light on the origins of life, but this does not just mean exoplanets; Webb will also help unravel the mysteries still held by objects in our own solar system (from Mars outward).
- Geronimo Villanueva, a planetary scientist at NASA/GSFC in Greenbelt, Maryland, is the lead scientist on the Webb telescope's observation of Europa and Enceladus. His team is part of a larger effort to study our solar system with the telescope, spearheaded by astronomer Heidi Hammel, the executive vice president of the Association of AURA (Universities for Research in Astronomy). NASA selected Hammel as an interdisciplinary scientist for Webb in 2002.
- Of particular interest to the scientists are the plumes of water that breach the surface of Enceladus and Europa, and that contain a mixture of water vapor and simple organic chemicals. NASA's Cassini-Huygens and Galileo missions, and NASA's Hubble Space Telescope, previously gathered evidence that these jets are the result of geologic processes heating large subsurface oceans. "We chose these two moons because of their potential to exhibit chemical signatures of astrobiological interest," said Hammel.
- Villanueva and his team plan to use Webb's near-infrared camera (NIRCam) to take high-resolution imagery of Europa, which they will use to study its surface and to search for hot surface regions indicative of plume activity and active geologic processes. Once they locate a plume, they will use Webb's NIRSpec (Near-Infrared Spectrograph) and MIRI (Mid-Infrared Instrument) to spectroscopically analyze the plume's composition.
- Webb telescope's observations might be particularly telling for the plumes on Europa, the composition of which largely remains a mystery. "Are they made of water ice? Is hot water vapor being released? What is the temperature of the active regions and the emitted water?" questioned Villanueva. "Webb telescope's measurements will allow us to address these questions with unprecedented accuracy and precision."
- For Enceladus, Villanueva explained that because that moon is nearly 10 times smaller than Europa as seen from the Webb telescope, high-resolution imagery of its surface will not be possible. However, the telescope can still analyze the molecular composition of Enceladus' plumes and perform a broad analysis of its surface features. Much of the moon's terrain has already been mapped by NASA's Cassini orbiter, which has spent about 13 years studying Saturn and its satellites.
- Villanueva cautioned that while he and his team plan to use NIRSpec to search for organic signatures (such as methane, methanol, and ethane) in the plumes of both moons, there is no guarantee the team will be able to time the Webb telescope's observations to catch one of the intermittent emissions, nor that the emissions will have a significant organic composition. "We only expect detections if the plumes are particularly active and if they are organic-rich," said Villanueva.
- Evidence of life in the plumes could prove even more elusive. Villanueva explained that while chemical disequilibrium in the plumes (an unexpected abundance or scarcity of certain chemicals) could be a sign of the natural processes of microbial life, it could also be caused by natural geologic processes.
- While the Webb telescope may be unable to concretely answer whether the subsurface oceans of the moons contain life, Villanueva said it will be able to pinpoint and better characterize active regions of the moons that could merit further study. Future missions, such as NASA's Europa Clipper, the primary objective of which is to determine if Europa is habitable, could use Webb's data to hone in on prime locations for observation.
Figure 120: Possible spectroscopy results from one of Europa's water plumes. This is an example of the data the Webb telescope could return (image credit: NASA-GSFC/SVS, Hubble Space Telescope, Stefanie Milam, Geronimo Villanueva)
• August 9, 2017: NASA's James Webb Space Telescope began a nearly 100-day cryogenic test in a giant chamber in Texas in mid-July. Components of the Webb have previously endured similar tests to ensure they would function in the cold environment of space. Now all of those components are being tested together in the giant thermal vacuum known as Chamber A at NASA's Johnson Space Center in Houston. 159)
- "A combination of liquid nitrogen and cold gaseous helium will be used to cool the telescope and science instruments to their operational temperature during high-vacuum operations," said Mark Voyton, manager of testing effort, who works at the NASA Goddard Space Flight Center in Greenbelt, Maryland.
- Next year, the tennis-court sized sunshield and spacecraft bus will be added to make up the entire observatory.
Figure 121: NASA's JWST sits in Chamber A at NASA's Johnson Space Center in Houston awaiting the colossal door to close (image credit: NASA, Chris Gunn)
• May 1, 2017: The JWST has successfully passed the center of curvature test, an important optical measurement of Webb's fully assembled primary mirror prior to cryogenic testing, and the last test held at NASA's Goddard Space Flight Center in Greenbelt, Maryland, before the spacecraft is shipped to NASA's Johnson Space Center in Houston for more testing. 160) 161)
- After undergoing rigorous environmental tests simulating the stresses of its rocket launch, the Webb telescope team at Goddard analyzed the results from this critical optical test and compared it to the pre-test measurements. The team concluded that the mirrors passed the test with the optical system unscathed.
- "The Webb telescope is about to embark on its next step in reaching the stars as it has successfully completed its integration and testing at Goddard. It has taken a tremendous team of talented individuals to get to this point from all across NASA, our industry and international partners, and academia," said Bill Ochs, NASA's Webb telescope project manager. "It is also a sad time as we say goodbye to the Webb Telescope at Goddard, but are excited to begin cryogenic testing at Johnson."
- The Webb telescope will be shipped to Johnson for end-to-end optical testing in a vacuum at its extremely cold operating temperatures. Then it will continue on its journey to Northrop Grumman Aerospace Systems in Redondo Beach, California, for final assembly and testing prior to launch in 2018.
• March 28, 2017: The JWST team completed the acoustic and vibration portions of environmental testing on the telescope at NASA/GSFC. These tests are merely two of the many that spacecraft and instruments endure to ensure they are fit for spaceflight. 162)
- For the acoustic test, the telescope was wrapped in a clean tent, and engineers and technicians pushed it through a large pair of insulated steel doors, nearly 30 cm thick, into the Acoustic Test Chamber. In the chamber the telescope was exposed to the earsplitting noise and resulting vibration of launch.
- A new vibration test system also known as a shaker table, was built specifically for testing the Webb. The Webb was mounted on the shaker table and experienced the simulated forces the telescope will feel during the launch by vibrating it from 5 to 100 times per second. The test ensures a spacecraft like Webb can withstand the vibrations that occur as a result of the ride into space on a rocket.
- This spring, after other environmental tests are completed, the Webb telescope will be shipped to NASA's Johnson Space Center in Houston, Texas, for end-to-end optical testing in a vacuum at its extremely cold operating temperatures, before it goes to Northrop Grumman Aerospace Systems in Redondo Beach, California, for final assembly and testing prior to launch.
- By performing these tests, scientists and engineers can ensure that the spacecraft and all of its instruments will endure the launch and maintain functionality when it is launched from French Guiana in 2018.
Figure 122: NASA engineers and technicians perform vibration testing on the James Webb Space Telescope (image credit: NASA, Chris Gunn)
• January 25, 2017: Engineers have resumed a series of critical and rigorous vibration qualification tests on JWST at NASA/GSFC. On December 3, 2016, vibration testing automatically shut down early due to some sensor readings that exceeded predicted levels. After a thorough investigation, the JWST team at NASA Goddard determined that the cause was extremely small motions of the numerous tie-downs or "launch restraint mechanisms" that keep one of the telescope's mirror wings folded-up for launch. 163)
- "In-depth analysis of the test sensor data and detailed computer simulations confirmed that the input vibration was strong enough and the resonance of the telescope high enough at specific vibration frequencies to generate these tiny motions. Now that we understand how it happened, we have implemented changes to the test profile to prevent it from happening again," said Lee Feinberg, an engineer and James Webb Space Telescope Optical Telescope Element Manager at Goddard. "We have learned valuable lessons that will be applied to the final pre-launch tests of Webb at the observatory level once it is fully assembled in 2018. Fortunately, by learning these lessons early, we've been able to add diagnostic tests that let us show how the ground vibration test itself is more severe than the launch vibration environment in a way that can give us confidence that the launch itself will be fully successful."
- The team resumed testing last week picking up where they left off in December. The test was successfully completed. Now that vibration testing along this one direction or "axis" is finished, the team is now moving forward with shaking the telescope in the other two directions to show that it can withstand vibrations in all three dimensions. "This was a great team effort between the NASA Goddard team, Northrop Grumman, Orbital ATK, Ball Aerospace, the European Space Agency, and Arianespace," Feinberg said. "We can now proceed with the rest of the planned tests of the telescope and instruments."
• January 3, 2017: Vibration tests are one of the many tests that spacecraft and instruments endure to ensure they are fit for spaceflight. During routine testing of NASA's James Webb Space Telescope, an unexpected response occurred from several of the more than 100 devices designed to detect small changes in the motion of the structure. This prompted the engineers put the vibration tests on hold to determine the cause. 164)
- Since then, the team of engineers and scientists have analyzed many potential scenarios for the measured responses. They are closer to pinning down the cause, and have successfully conducted three low-level vibrations of the telescope.
- All visual and ultrasonic examinations of the structure continue to show it to be sound. "Currently, the team is continuing their analyses with the goal of having a review of their findings, conclusions and plans for resuming vibration testing in January," said Eric Smith, program director for NASA's James Webb Space Telescope, NASA Headquarters in Washington.
- "This is why we test—to know how things really are, as opposed to how we think they are," said Paul Geithner, deputy project manager-technical for the Webb telescope at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
- During the vibration tests on December 3, 2016 at NASA/GSFC, accelerometers attached to the telescope detected unexpected responses and consequently the test shut itself down to protect the hardware.
- The test shut itself down in a fraction of a second after a higher-than-expected response was detected at a particular frequency of vibration, about one note lower than the lowest note on a piano.
- At NASA, vibration and acoustics test facilities provide vibration and shock testing of spaceflight hardware to ensure that functionality is not impaired by severe launch and landing environments. Launches create high levels of vibration in spacecraft and equipment and ground testing is done to simulate that launch induced vibration. Vibration testing is done on components as small as a few ounces to as large as complete structures or systems.
- By performing the vibration tests on NASA's James Webb Space Telescope, scientists and engineers can ensure that the spacecraft and all of its instruments will endure the launch and maintain functionality when it is launched from French Guiana in 2018.
• November 2, 2016: Engineers and technicians working on the James Webb Space Telescope successfully completed the first important optical measurement of Webb's fully assembled primary mirror, called a Center of Curvature test. 165)
- Taking a "before" optical measurement of the telescope's deployed mirror is crucial before the telescope goes into several stages of rigorous mechanical testing. These tests will simulate the violent sound and vibration environments the telescope will experience inside its rocket on its way out into space. This environment is one of the most stressful structurally and could alter the shape and alignment of Webb's primary mirror, which could degrade or, in the worst case, ruin its performance.
- The JWST has been designed and constructed to withstand its launch environment, but it must be tested to verify that it will indeed survive and not change in any unexpected way. Making the same optical measurements both before and after simulated launch environment testing and comparing the results is fundamental to Webb's development, assuring that it will work in space.
- "This is the only test of the entire mirror where we can use the same equipment during a before and after test," said Ritva Keski-Kuha, the test lead and NASA's Deputy Telescope Manager for Webb at NASA/GSFC in Greenbelt, Maryland. "This test will show if there are any changes or damages to the optical system."
- In order to conduct the test, optical engineers set up an interferometer, the main device used to measure the shape of Webb's mirror. Waves of visible light are less than a thousandth of a millimeter long, and optics like Webb's need to be shaped and aligned even more accurately than this to work correctly. Making measurements of the mirror shape and position by lasers prevents physical contact and damage (scratches to the mirror). So scientists use wavelengths of light to make tiny measurements. By measuring light reflected off the optics using an interferometer, they are able to measure extremely small changes in shape or position. An interferometer gets its name from the process of recording and measuring the ripple patterns that result when different beams of light mix and their waves combine or 'interfere.'
- During the test conducted by a team from NASA Goddard, Ball Aerospace of Boulder, Colorado, and the Space Telescope Science Institute in Baltimore Maryland, temperature and humidity conditions in the cleanroom were kept incredibly stable to minimize drift in the sensitive optical measurements over time. Even so, tiny vibrations are ever-present in the cleanroom that cause jitter during measurements, so the interferometer is a 'high-speed' one, taking 5,000 'frames' every second, which is a faster rate than the background vibrations themselves. This allows engineers to subtract out jitter and get good, clean results.
- The Center of Curvature test measures the shape of Webb's main mirror by comparing light reflected off of it with light from a computer-generated hologram that represents what Webb's mirror ideally should be. By interfering the beam of light from Webb with the beam from the hologram reference, the interferometer accurately compares the two by measuring the difference to incredible precision. "Interferometry using a computer-generated hologram is a classic modern optical test used to measure mirrors," said Keski-Kuha.
- With the largest mirror of any space telescope, taking this measurement is a challenge. "We have spent the last four years preparing for this test," said David Chaney, Webb's primary mirror metrology lead at Goddard. "The challenges of this test include the large size of the primary mirror, the long radius of curvature, and the background noise. Our test is so sensitive we can measure the vibrations of the mirrors due to people talking in the room."
- After the measurements come back from the interferometer the team will analyze the data to make sure the mirrors are aligned perfectly before the launch environment tests. The Center of Curvature test will be repeated after the launch environment testing and the results compared to confirm that Webb's optics will work after their launch into space.
- The most powerful space telescope ever built, the Webb telescope will provide images of the first galaxies ever formed, and explore planets around distant stars. It is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
Figure 123: Engineers conduct a 'Center of Curvature' test on NASA's James Webb Space Telescope in the clean room at NASA's Goddard Space Flight Center, Greenbelt, Maryland (image credit: NASA, Chris Gunn)
• October 31, 2016: The last of the five sunshield layers responsible for protecting the optics and instruments of NASA's James Webb Space Telescope is now complete. Designed by Northrop Grumman in Redondo Beach, California, the Webb telescope's sunshield will prevent the background heat from the sun from interfering with the telescope's infrared sensors. The five sunshield membrane layers, designed and manufactured by the NeXolve Corporation in Huntsville, Alabama, are each as thin as a human hair. The layers work together to reduce the temperatures between the hot and cold sides of the observatory by approximately 300ºC. Each successive layer of the sunshield, made of Kapton, is cooler than the one below. The fifth and final layer was delivered on Sept. 29, 2016 to Northrop Grumman Corporation's Space Park facility in Redondo Beach. 166)
- "The completed sunshield membranes are the culmination of years of collaborative effort by the NeXolve, Northrop Grumman and NASA team," said James Cooper, Webb telescope Sunshield manager at NASA Goddard Space Flight Center in Greenbelt, Maryland. "All five layers are beautifully executed and exceed their requirements. This is another big milestone for the Webb telescope project."
- Northrop Grumman, who also designed the Webb telescope's optics and spacecraft bus for NASA Goddard will integrate the final flight layers into the sunshield subsystem to conduct folding and deployment testing as part of the final system validation process. The sunshield is the size of a tennis court, helping solidify the Webb telescope as the largest ever built for space. The sunshield, along with the rest of the spacecraft, will fold origami-style into an Ariane 5 rocket.
- "The five tennis court-sized sunshield membranes took more than three years to complete and represents a decade of design, development and manufacturing," said Greg Laue, sunshield program manager at NeXolve.
Figure 124: Photo of the JWST sunshield at Northrop Grumman's Space Park facility in Redondo Beach, California (image credit: Northrop Grumman)
• May 24, 2016: With surgical precision, two dozen engineers and technicians successfully installed the package of science instruments of the James Webb Space Telescope into the telescope structure (Figure 125). The package is the collection of cameras and spectrographs that will record the light collected by Webb's giant golden mirror. 167)
- Inside the world's largest clean room at NASA's Goddard Space Flight Center in Greenbelt, Maryland, the team crane-lifted the heavy science instrument package, lowered it into an enclosure on the back of the telescope, and secured it to the telescope.
- Now that the instruments, mirrors, and telescope structure have been assembled, the combination will go through vibration and acoustic tests in order to ensure the whole science payload will withstand the conditions of launch.
Figure 125: In this view, the James Webb Space Telescope team crane lifted the science instrument package for installation into the telescope structure (image credit: NASA, Chris Gunn)
• April 27, 2016: NASA engineers recently unveiled the giant golden mirror of NASA's JWST (James Webb Space Telescope) as part of the integration and testing of the infrared telescope. The 18 mirrors that make up the primary mirror were individually protected with a black covers when they were assembled on the telescope structure. Now, for the first time since the primary mirror was completed, the covers have been lifted. 168)
- Scientists from around the world will use this unique observatory to capture images and spectra of not only the first galaxies to appear in the early universe over 13.5 billion years ago, but also the full range of astronomical sources such as star forming nebulae, exoplanets, and even moons and planets within our own Solar System. To ensure the mirror is both strong and light, the team made the mirrors out of beryllium. Each mirror segment is about the size of a coffee table and weighs approximately 20 kg. A very fine film of vaporized gold coats each segment to improve the mirror's reflection of infrared light. The fully assembled mirror is larger than any rocket so the two sides of it fold up. Behind each mirror are several motors so that the team can focus the telescope out in space.
Figure 126: Standing tall and glimmering gold inside the NASA/GSFC clean room in Greenbelt, Maryland is the James Webb Space Telescope primary mirror. It will be the largest yet sent into space (image credit: NASA, Chris Gunn)
• March 21, 2016: After over a year of planning, nearly four months of final cryo testing and monitoring, the testing on the science instruments module of the observatory was completed. They were removed from a giant thermal vacuum chamber at NASA/GSFC in Greenbelt, Maryland called the SES (Space Environment Simulator) that duplicates the vacuum and extreme temperatures of space. The SES is a 12 m tall, 8.3 m diameter cylindrical chamber that eliminates almost all of the air with vacuum pumps and uses liquid nitrogen and even colder gaseous helium to drop the temperature. 169)
- The testing is critical because at these instrument's final destination in space at L2, 1.5 million km away from Earth, it will operate at incredibly cold temperatures of 40 K. The science instrument modules tested consist of MIRI (Mid Infrared Instrument), jointly developed by a nationally funded European Consortium under the auspices of ESA (European Space Agency) and the JPL (Jet Propulsion Laboratory); NIRSpec (Near Infrared Spectrometer), jointly developed by Airbus for ESA and the U.S.; FGS/NIRISS (Fine Guidance Sensor/ Near-InfraRed Imager and Slitless Spectrograph), provided by CSA (Canadian Space Agency) and developed by COM DEV International, Cambridge, Ontario, Canada; and NIRCam (Near Infrared Camera), built by a team at the University of Arizona and Lockheed Martin's Advanced Technology Center.
• March 7, 2016: The sole secondary mirror that will fly aboard NASA's James Webb Space Telescope was installed onto the telescope at NASA's Goddard Space Flight Center in Greenbelt, Maryland, on March 3, 2016. 170)
• Feb. 24, 2016: The year 2015 marked big progress on NASA's James Webb Space Telescope and there are still a number of large milestones before the next generation telescope is launched in 2018. Recently, all of the 18 segments of the Webb telescope primary mirror segments were installed on the observatory's backplane at NASA's Goddard Space Flight Center in Greenbelt, Maryland. But that's just one component of the Webb. 171)
- Over the next two years, more components of the Webb will be integrated onto the spacecraft and it will visit three more locations before launch. "From 2016 to 2018, there are installations and tests for the telescope and the telescope plus the instruments, followed by shipping to NASA's Johnson Space Center in Houston, Texas where end-to-end optical testing in a simulated cryo-temperature and vacuum space environment will occur," said Paul Geithner, Webb telescope manager - Technical, at NASA Goddard. "Then all the parts will be shipped to Northrop Grumman for final assembly and testing, then to French Guiana for launch."
- The two largest parts of the observatory are the primary mirror and the tennis-court-sized sunshield. Additionally, there are four scientific instruments—cameras and spectrographs with detectors able to record extremely faint signals—that will fly aboard Webb. All four flight science instruments were integrated into the ISIM (Integrated Science Instrument Module) in March 2014 and since have been undergoing multiple tests. However, the ISIM has not yet been added to the observatory.
- Over the next year, teams at Goddard will work to complete the telescope by installing the other optics in addition to the primary mirror segments. The other optics include installing the aft-optics subsystem or AOS, secondary mirror and both fixed and deployed radiators. Once complete, engineers will connect the Telescope and instruments together when the ISIM is attached to the observatory.
- Testing is a continuous part of the assembly process. "After the mating of the ISIM, to the Telescope there will be a room-temperature optical check before a simulated launch environment exposure," Geithner said. That means the observatory will undergo vibration and acoustic testing to ensure it can endure the sound and shaking that occurs during launch. After those tests, there is yet another room-temperature optical check.
- Once all of those milestones are accomplished, the observatory will then be prepared and flown to NASA's Johnson Space Center, Houston, Texas. At Johnson, the observatory will endure end-to-end optical testing in a simulated cryo-temperature and vacuum space environment in Chamber-A. Chamber-A is NASA's giant thermal vacuum chamber where the Webb telescope pathfinder or non-flight replica was tested in April 2015.
- After NASA/JSC, the Webb telescope will be then transported to Northrop Grumman in Redondo Beach, California where engineers will connect the telescope and instruments together with the spacecraft and sunshield to form the complete Observatory. Once every component is together, more testing is done. That testing is called "Observatory-level testing." It's the last exposure to a simulated launch environment before flight and deployment testing on the whole observatory.
- What follows the flight and deployment testing is the shipping of the complete observatory to the launch site in South America where the Webb telescope is slated to launch in 2018.
• At NASA/GSFC (Goddard Space Flight Center):
- Aft-Optics System installation
- Secondary mirror installation
- ISIM (Integrated Science Instrument Module) installation into Telescope Structure
- Metrology test of Telescope and Instruments
- Vibration test of Telescope and Instruments
- Acoustic test of Telescope and Instruments
• At NASA/JSC (Johnson Space Center):
- Optical test of Telescope and Instruments in Chamber A
• At Northrop Grumman:
- Assemble Spacecraft Element
- Finish Sunshield and Integrate into Spacecraft
- Assembling entire Observatory (Telescope and Instruments and Spacecraft)
- Observatory-level tests
- Transport to French Guiana
Table 14: A general list of milestones before launch (Ref. 171)
• February 4, 2016: The 18th and final primary mirror segment is installed on what will be the biggest and most powerful space telescope ever launched. The final mirror installati at NASA's Goddard Space Flight Center in Greenbelt, Maryland marks an important milestone in the assembly of the agency's James Webb Space Telescope. 172)
- Using a robotic arm reminiscent of a claw machine, the team meticulously installed all of Webb's primary mirror segments onto the telescope structure. Each of the hexagonal-shaped mirror segments measures just 1.3 m across with a mass of ~40 kg. Once in space and fully deployed, the 18 primary mirror segments will work together as one large 6.5 m diameter mirror.
- The mirrors were built by Ball Aerospace & Technologies Corp., in Boulder, Colorado. Ball is the principal subcontractor to Northrop Grumman for the optical technology and optical system design. The installation of the mirrors onto the telescope structure is performed by Harris Corporation, a subcontractor to Northrop Grumman. Harris Corporation leads integration and testing for the telescope.
Figure 127: In this rare view, the JWST's 18 mirrors are seen fully installed on the JWST structure at NASA/GSFC in Greenbelt (image credit: NASA, Chris Gunn)
• Dec. 28, 2015: As the year 2015 comes to an end, the assembly of the JWST reached the halfway point in the installation of the primary mirrors onto the telescope structure. Technicians have just installed the ninth of 18 primary flight mirrors onto the mirror holding backplane structure at the NASA/GSFC in Greenbelt, MD. 173)
Figure 128: This overhead photo of JWST shows the nine primary flight mirrors installed on the telescope structure in a clean room at NASA/GSFC (image credit: NASA/GSFC, Chris Gunn)
• Nov. 25, 2015: NASA has successfully installed the first of 18 flight mirrors onto the James Webb Space Telescope, beginning a critical piece of the observatory's construction. In the clean room at NASA/GSFC this week, the engineering team used a robot arm to lift and lower the hexagonal-shaped segment that measures just over 1.3 m with a mass of ~40 kg. After being pieced together, the 18 primary mirror segments will work together as one large 6.5 m mirror. The full installation is expected to be complete early next year. 174)
Figure 129: An engineer at NAS/GSFC worked to install the first flight mirror onto the telescope structure (image credit: NASA, Chris Gunn)
• Nov. 16, 2015: Inside the clean room at NASA/GSFC, engineers successfully completed two deployments for the James Webb Space Telescope's "wings" or side portions of the backplane structure that fold up. The wings and telescope structure are essential because they make up the telescope's carbon fiber framework which will hold all 18 of the telescope's mirrors and the tower for the primary mirror.175)
- "We deploy the wings one at a time. Each individual deployment can take up to 16 hours or more to complete," said Adam Carpenter, Mechanical Integration Engineer at Goddard, as he and other engineers prepared for the move. "It is a delicate operation requiring multiple groups to perform specific tasks." Leading up to this test, engineers lined the telescope structure with cables. In space, these cables will enable the telescope to open up and will provide electrical signals to the active the mirror segments. During the wing test, however, the engineers needed to make sure the cables did not block the deployment, and so the team arranged the cables carefully.
- "The two wings of the telescope structure will eventually hold 6 of Webb's 18 primary mirror segment assemblies," said Carpenter said. "They are necessary so that the observatory can fold up in order to fit into the launch vehicle." The James Webb Space telescope, once fully assembled, will be bigger than any rocket that can launch the telescope into space. So the engineering team designed the telescope to fold like origami to fit inside its Ariane 5 rocket.
Figure 130: Engineers successfully completed two deployments for the James Webb Space Telescope's "wings" or side portions of the backplane structure that fold up (image credit: NASA)
• October 8, 2015: Northrop Grumman is reporting that the manufacturing and assembly of the JWST spacecraft structure was successfully completed July 1 at NGC's (Northrop Grumman Corporation's) Redondo Beach facility (Figure 131). 176)
- The bus must withstand a force equivalent to 45 tons while supporting the observatory during launch. The spacecraft structure integrates the system's optical telescope, sunshield, and instrument electronics and mounts the whole observatory to the Ariane 5 rocket — tasked with launching the Webb Telescope to its destination in space. To launch such a large observatory out to the L2 orbit 1.5 km away, the structure must also be of very low mass so its mass efficiency allows it to carry 64 times its own mass.
Figure 131: Photo of the JWST bus structure which is made of carbon fiber composites and houses the spacecraft propulsion, electrical power and the communication systems (image credit: NGC, NASA)
• Sept. 16, 2015: The flight structure of NASA's JWST was standing tall on a platform in the cleanroom at NASA's Goddard Space Flight Center in Greenbelt, Maryland on August 30 (Figure 132). The telescope structure includes the primary mirror backplane assembly; the main backplane support fixture; and the deployable tower structure that lifts the telescope off of the spacecraft. The three arms at the top come together into a ring where the secondary mirror will reside. 177)
- Standing tall and standing up in the stowed-for-launch configuration as it appears in this photo, the complete telescope structure stretches about 8 m from its base on the roll-over fixture to the secondary mirror support at the top. There is a yellow fixture at the bottom of the telescope structure that is designed to secure the bottom of the tower until the telescope structure is mounted on the spacecraft.
- In late fall, Webb's hexagonal flight mirrors will be placed by a robotic arm onto the backplane, which will hold the hexagonal mirrors and instruments steady while the telescope is looking into deep space. Together, those 18 mirrors make up Webb's 6.5 m diameter "primary mirror." Along with the secondary, tertiary, and fine steering mirrors, this primary mirror comprises a telescope that will help scientists observe the formation of the first stars and galaxies over 13.5 billion years ago.
- In addition to the primary mirror, the backplane will also be carrying 2400 kg of telescope optics and instruments. The backplane must keep the mirrors motionless in order to get clear images far in deep space. It was engineered to remain stationary down to about 1/10,000 the diameter of a human hair (32 nm) at temperatures colder than -240°C, such as those experienced in space.
- The flight backplane arrived at Goddard after undergoing integration and testing at Northrop Grumman Aerospace Systems in Redondo Beach, California. ATK designed, engineered and constructed the backplane at its facilities in Magna, Utah. Once the backplane arrived, it was inspected by engineers and then set upright using a giant crane in the clean room.
Figure 132: Photo of the JWST in the cleanroom of NASA/GSFC (image credit: NASA, C. Gunn)
• August 12, 2015: The sunshield on NASA's James Webb Space Telescope is the largest part of the observatory—five layers of thin, silvery membrane that must unfurl reliably in space. The precision in which the tennis-court sized sunshield has to open must be no more than a few centimeters different from its planned position (Figure 133). 178)
- The sunshield separates the observatory into a warm sun-facing side and a cold side where the sunshine is blocked from interfering with the sensitive infrared instruments. The infrared instruments need to be kept very cold (under 50 K to operate. The sunshield protects these sensitive instruments with an effective SPF (Sun Protection Factor) of 1,000,000. A sunscreen generally has an SPF of 8 to 50.
Figure 133: In this photo, engineers and scientists examine the sunshield layers on this full-sized test unit. Because there's a layer of the shiny silver material on the base under the five layers of the sunshield, it appears as if the sunshield has a mouth that is "open wide" while engineers take a look. The photo was taken in a clean room at Northrop Grumman Corporation, Redondo Beach, California.. (image credit: NASA)
• Summer 2015: The JWST team has just successfully completed the first of three planned, large-scale pathfinder tests at the Chamber A facility at Johnson Space Center in Houston, Texas. These tests are designed to verify the operation of the support and test equipment as well as check critical alignment and test procedures, train personnel, and improve test efficiency in preparation for the final, full scale flight testing of JWST scheduled for Winter, 2016-2017. 179)
- This first pathfinder test, denoted OGSE1 (Optical Ground Support Equipment test 1), incorporated an engineering version of the JWST composite backplane (the mounting and support system for the telescope), two spares of the eighteen primary mirror segments and a flight spare secondary mirror and support structure.
- The next pathfinder test (OGSE2 - currently scheduled for Fall, 2015) will add the flight AOS (Aft-Optics-System) incorporating the flight tertiary and fine steering mirrors as well as a set of precisely located sources ASPA (AOS Source Plate Assembly) which will be imaged through the telescope system.
- A third, primarily thermal model validation pathfinder, is scheduled for testing in spring 2016.
• April 20, 2015: Inside NASA's giant thermal vacuum chamber, called Chamber A, at NASA's Johnson Space Center in Houston, the James Webb Space Telescope's Pathfinder backplane test model, is being prepared for its cryogenic test. Previously used for manned spaceflight missions, this historic chamber is now filled with engineers and technicians preparing for a crucial test. Exelis developed and installed the optical test equipment in the chamber. 180)
- "This will be the first time on the program that we will be aligning two primary mirror segments together," said Lee Feinberg, NASA Optical Telescope Element Manager. "In the past, we have always tested one mirror at a time, but this time we will use a single test system and align both mirrors to it as though they are a single monolithic mirror."
Figure 134: Photo of the JWST telescope pathfinder backplane test model in Chamber A at NASA/JSC (Johnson Space Center) in Houston (image credit: NASA, Chris Gunn)
• March 17-18, 2015: John Durning, JWST Deputy Program Manager, presented a current general status of the JWST project at the Astrophysics Subcommittee Meeting . He remarked that the schedule is healthy, with 10 months of critical path slack. The milestones are such that a lot of hardware will be delivered in FY16. Almost all hardware has passed critical design review (CDR). There was a late thermal challenge with the radiator, but that is catching up. The mission is deep into building and testing at this point. 181) 182)
- OTE (Optical Telescope Element): The flight telescope build begins in August 2015. All flight backplane components are built and are at Northrop Grumman for integration.
- The sunshield is making good progress and the team has done a practice deployment, including integration onto a practice spacecraft. There is a lot of testing and verification going on, as this is a key risk reduction activity. The flight membranes are in varying levels of completion.
- Four instruments make up the ISIM payload: the Fine Guidance Sensor (FGS) from Canada, the MIRI from Europe, the Near Infra-Red Camera (NIRCam), and the Near Infra-Red Spectrometer (NIRSpec). The spacecraft is not as far along in integration and testing, but the components are coming together.
- There will be three risk reductions tests this year for the Optical Telescope and ISIM (OTIS). Each test establishes the procedures and processes for higher- level assembly, giving confidence that the procedures work.
- Two of the three MIRI cryocooler components have been delivered, but the compressor assembly is taking longer than expected. Still, it should be delivered to JPL this summer. On the NIRSpec microshutter control electronics, there was a shorted wire during testing. The team is therefore rebuilding the affected board and the adjacent board; these will be delivered next month. The NIRCam detector system tests found that two of the four detector chips on one of the instrument channels had anomalous readings. Replacement of those units will be completed by the end of the month.
Figure 135: Simplified schedule of the JWST project (image credit: NASA, John Durning)
• The Figure 136 is a photo of the ISIM (Integrated Science Instrument Module), released by ESA on March 2, 2015. ISIM is a structure containing the four science infrared instruments of JWST. The JWST team hit a milestone in the summer of 2014 as all four science instruments passed their cryogenic testing in this chamber, the SES (Space Environment Simulator). The three near-infrared units were cooled to around –233°C, while the MIRI (Mid-Infrared Instrument) reached an even lower –266°C, for a total of 116 days. 183)
Figure 136: The gold-colored structure is the ISIM inside the Goddard Thermal Vacuum Chamber (image credit: NASA/GSFC, C. Gunn)
Legend to Figure 136: The photographer, wielding a torch at the bottom of the SES, took his picture of ISM prior to the cooling test in 2014.
• Oct. 21, 2014: After 116 days of being subjected to extremely frigid temperatures like that in space, the heart of the James Webb Space Telescope, the ISIM (Integrated Science Instrument Module) and its sensitive instruments, emerged unscathed from the thermal vacuum chamber at NASA/GSFC (Goddard Space Flight Center) in Greenbelt, Maryland. 184)
- SES (Space Environment Simulator) is the name of the massive thermal vacuum chamber, that duplicates the vacuum and extreme temperatures of space. SES is a cylindrical chamber of 12 m in height and 8.3 m in diameter which was kept at a temperature of 40 K during the ISIM test. SES eliminates the tiniest trace of air with vacuum pumps and uses liquid nitrogen and even colder liquid helium to drop the temperature simulating the space environment.
- These tests were conducted to make sure that when JWST cools down in space, the four instruments of ISIM are still positioned meticulously so that when light enters the telescope, it is captured in the right way. Paul Geithner, the JWST deputy project manger, commented: "The biggest stress for this telescope will be when it cools down. When the telescope structure goes from room temperature to its super cold operating temperature (of ~ 35 K), it will see more stress from shrinkage than it will from violent vibration during launch."
- Once the test was completed, the team warmed up the chamber, and completed the final functional test and a series of data analyses before they opened up the chamber.
Figure 137: A crane lifts ISIM, the heart of the JWST, from the Goddard Thermal Vacuum Chamber where it spent 116 days in a space-like environment (image credit: NASA, Chris Gunn)
• In July 2014, the sunshield of JWST was fully and successfully tested for the first time, at a cleanroom in the Northrop Grumman facility in Redondo Beach, CA, USA. 185) 186)
The Sunshield is the largest part of the Webb telescope (about the size of a tennis court). The five layers of thin membrane called Kapton, that feels like a Mylar balloon, must unfurl reliably in space like a parasol. The sunshield provides a cold-side stable environment of < 50 K to permit in particular top quality measurements of the instruments in the far infrared region of the spectrum. - The Sunshield will be folded up like an umbrella around the Webb telescope's mirrors and instruments during launch. Once it reaches its orbit, the Webb telescope will receive a command from Earth to unfold, and separate the sunshield's five layers into their precisely stacked arrangement with its kite-like shape.
Thanks to the sunshield, these low temperatures are reached passively, without the help of any active cooling system, by re-radiating the sun's heat into deep space. Just one of JWST's instruments, MIRI (Mid-Infrared Instrument), will be cooled even further by a dedicated cryogenic cooler, reaching around 7 K (–266 ºC ). Although parts of JWST will reach such low temperatures, the shield will create a thermal barrier so that on JWST's 'hot' side, the spacecraft electronics can work at room temperature.
Figure 138: Photo of the fully deployed sunshield in the Northrop Grumman cleanroom (image credit: NASA, Chris Gunn)
• During the summer of 2014, a milestone event in the JWST test program is underway: the first of two cryo-verification tests of the complete ISIM (Integrated Science Instrument Module). Pumpdown for this critical test began a few weeks ago in Goddard's largest thermal-vacuum chamber, the SES (Space Environment Simulator). The team expects the test will continue for about 110 days. 187)
• In August 2014, the central piece of the "pathfinder" backplane that will hold all the mirrors for JWST, has arrived at the agency's Goddard Space Flight Center in Maryland for critical assembly testing on vital parts of the mammoth telescope. 188)
• In July 2014, the JWST has reached another development milestone with the completion of static load testing of its primary mirror backplane support structure (PMBSS) moving the telescope one step closer to its 2018 launch. The PMBSS is the stable platform that holds the telescope's science instruments and the 18 beryllium mirror-segments that form the 6.5 m diameter primary mirror nearly motionless while the telescope peers into deep space. The primary mirror is the largest mirror in the telescope — the one starlight will hit first. 189)
• In January 2014, JWST has passed its first significant mission milestone for 2014, the SCDR (Spacecraft Critical Design Review) that examined the telescope's power, communications and pointing control systems. 190) 191) 192)
During the SCDR, the details, designs, construction and testing plans, and the spacecraft's operating procedures were subjected to rigorous review by an independent panel of experts. The week-long review involved extensive discussions on all aspects of the spacecraft to ensure the plans to finish construction would result in a vehicle that enables the powerful telescope and science instruments to deliver their unique and invaluable views of the universe.
JWST continued
Introduction of JWST spinoff technologies:
In the timeframe 2010/12, new technologies developed for NASA's JWST (James Webb Space Telescope) have already been adapted and applied to commercial applications in various industries including optics, aerospace, astronomy, medical and materials. Some of these technologies can be explored for use and licensed through NASA's Office of the Chief Technologist at NASA's Goddard Space Flight Center, Greenbelt, MD. - Note: NASA's JWST is also simply referred to as the Webb. 193) 194)
1) Optics Industry: Telescopes, Cameras and More
The optics industry has been the beneficiary of a new stitching technique that is an improved method for measuring large aspheres. An asphere is a lens whose surface profiles are not portions of a sphere or cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.
Stitching is a method of combining several measurements of a surface into a single measurement by digitally combining the data as though it has been "stitched" together.
Because NASA depends on the fabrication and testing of large, high-quality aspheric (nonspherical) optics for applications like the JWST, it sought an improved method for measuring large aspheres. Through SBIR (Small Business Innovation Research) awards from NASA/GSFC, QED Technologies, of Rochester, New York, upgraded and enhanced its stitching technology for aspheres.
QED developed the SSI-A® (Subaperture Stitching Interferometer for Aspheres) metrology technology, which earned the company an "R and D 100" award, and also developed a breakthrough machine tool called the aspheric stitching interferometer. The equipment is applied to advanced optics in telescopes, microscopes, cameras, medical scopes, binoculars, and photolithography.
2) Aerospace and Astronomy
In the aerospace and astronomy industries, the JWST program gave 4D Technology its first commercial contract to develop the PhaseCam interferometer system, which measures the quality of the JWST telescope's mirror segments in a cryogenic vacuum environment. This is a new way of using interferometers in the aerospace sector.
• The PhaseCam interferometer verified that the surfaces of the JWST telescope's mirror segments were as close to perfect as possible, and that they will remain that way in the cold vacuum of space. To test the Webb mirror segments, they were placed in a "cryovac" environment, where air is removed by a vacuum pump and temperatures are dropped to the extreme cold of deep space that the space craft will experience. A new dynamic interferometric technique with very short exposures that are not smeared by vibration was necessary to perform these measurements to the accuracy required, particularly in the high-vibration environment caused by the vacuum chamber's pumps. - The interferometer resulting from this NASA partnership can be used to evaluate future mirrors that need to be tested in vacuum chambers where vibration is a problem.
• Restoring Hubble: Integrated circuits used in camera repair. Webb investments in cryogenic ASICs (Application-Specific Integrated Circuits) led to the development of the ASICs that are now flying on the Hubble Space Telescope. This is a unique example of "future heritage": a program in development (Webb) invented a technology for a program well into the operations phase (Hubble). Webb's investments into this technology allowed the ASICs to be programmable, which was important in the repair of Hubble's Advanced Camera for Surveys that has produced stunning views of our universe.
• Astronomical Detectors: The benefits of the near-infrared detectors developed for Webb's instruments have already spread far and wide in the world of science. "Infrared sensors based on the technology developed for Webb are now the universal choice for astronomical observations, both from space and the ground," said Dr. James Beletic, Senior Director at Teledyne. This technology is also being used for Earth science and national security missions. An early pathfinder version of Webb's HAWAII-2RG 4 Megapixel array has been used in several NASA missions including Hubble, Deep Impact/EPOXI, WISE, and the OCO-2 (Orbiting Carbon Observatory-2), and the HAWAII-2RG is already in use at dozens of ground-based observatories around the world. The availability of these high-performance detectors developed for Webb has been critical to a breathtaking collection of missions, both present and future (Ref. 194).
3) Medical Industry: Eye Health
New "wavefront" optical measurement devices and techniques were created for making the JWST telescope mirrors. Those have led to spinoffs in the medical industry where precise measurements are critical in eye health, for example.
• The technology came about to accurately measure the JWST primary mirror segments during manufacturing. Scientists at AMO WaveFront Sciences, LLC of Albuquerque, N.M. developed a new "wavefront" measurement device called a Scanning Shack Hartmann Sensor.
• The optical measuring technology developed for the JWST, called "wavefront sensing" has been applied to the measurement of the human eye and allowed for significant improvements.
• "The Webb telescope program has enabled a number of improvements in measurement of human eyes, diagnosis of ocular diseases and potentially improved surgery," said Dan Neal, Director of Research and Development AMO (Abbott Medical Optics Inc.) in Albuquerque, N.M. The Webb improvements have enabled eye doctors to get much more detailed information about the shape and "topography" of the eye in seconds rather than hours.
4) Materials Industry: Measuring Strength
The JWST technologies have opened the door to better measurement in testing the strength of composite materials. Measuring strain in composite materials is the same as measuring how much they change in certain environments. Measuring step heights allows one to understand very small changes in a surface profile and doing all of this at high speed allows the device to work even in the presence of vibration that would normally blur the results.
"Technology developed for the Webb telescope has also helped 4D Technologies, Inc. to develop unique technology to measure strain in composite materials, to measure step heights in precision machined surfaces, and for high speed wavefront detection," said James Millerd, President, 4D Technology Corporation, Tucson, AZ.
The Webb telescope technologies have also been beneficial to the economy. The technologies have enabled private sector companies such as 4D to generate significant revenue and create high-skill jobs. Much of 4D's growth from a two man start-up to over 35 people can be traced to projects originally developed for the telescope. 4D has also been able to adapt these technologies for a wide range of applications within the astronomy, aerospace, semiconductor and medical industries.
Feature Stories of the Solar System and Beyond
• October 27, 2021: In its first year of operations, NASA's James Webb Space Telescope will join forces with a global collaborative effort to create an image of the area directly surrounding the supermassive black hole at the heart of our Milky Way galaxy. The Event Horizon Telescope (EHT) is famous for its first image of the "shadow" of the black hole at the core of galaxy M87, and it has now turned its efforts to the more complex environment of Sagittarius A*, the Milky Way's supermassive black hole. While M87's core presented a steady target, Sagittarius A* exhibits mysterious flickering flares on an hourly basis, which make the imaging process much more difficult. Webb will assist with its own infrared images of the black hole region, providing data about when flares are present that will be a valuable reference to the EHT team. 195)
- On isolated mountaintops across the planet, scientists await word that tonight is the night: The complex coordination between dozens of telescopes on the ground and in space is complete, the weather is clear, tech issues have been addressed—the metaphorical stars are aligned. It is time to look at the supermassive black hole at the heart of our Milky Way galaxy.
- This "scheduling Sudoku," as the astronomers call it, happens each day of an observing campaign by the Event Horizon Telescope (EHT) collaboration, and they will soon have a new player to factor in; NASA's James Webb Space Telescope will be joining the effort. During Webb's first slate of observations, astronomers will use its infrared imaging power to address some of the unique and persistent challenges presented by the Milky Way's black hole, named Sagittarius A* (Sgr A*; the asterisk is pronounced as "star").
- In 2017, EHT used the combined imaging power of eight radio telescope facilities across the planet to capture the historic first view of the region immediately surrounding a supermassive black hole, in the galaxy M87. Sgr A* is closer but dimmer than M87's black hole, and unique flickering flares in the material surrounding it alter the pattern of light on an hourly basis, presenting challenges for astronomers.
- "Our galaxy's supermassive black hole is the only one known to have this kind of flaring, and while that has made capturing an image of the region very difficult, it also makes Sagittarius A* even more scientifically interesting," said astronomer Farhad Yusef-Zadeh, a professor at Northwestern University and principal investigator on the Webb program to observe Sgr A*.
Figure 139: An enormous swirling vortex of hot gas glows with infrared light, marking the approximate location of the supermassive black hole at the heart of our Milky Way galaxy. This multiwavelength composite image includes near-infrared light captured by NASA's Hubble Space Telescope, and was the sharpest infrared image ever made of the galactic center region when it was released in 2009 . Dynamic flickering flares in the region immediately surrounding the black hole, named Sagittarius A*, have complicated the efforts of the Event Horizon Telescope (EHT) collaboration to create a closer, more detailed image. While the black hole itself does not emit light and so cannot be detected by a telescope, the EHT team is working to capture it by getting a clear image of the hot glowing gas and dust directly surrounding it. - NASA's upcoming James Webb Space Telescope, scheduled to launch in December 2021, will combine Hubble's resolution with even more infrared light detection. In its first year of science operations, Webb will join with EHT in observing Sagittarius A*, lending its infrared data for comparison to EHT's radio data, making it easier to determine when bright flares are present, producing a sharper overall image of the region. - In the composite image shown here, colors represent different wavelengths of light. Hubble's near-infrared observations are shown in yellow, revealing hundreds of thousands of stars, stellar nurseries, and heated gas. The deeper infrared observations of NASA's Spitzer Space Telescope are shown in red, revealing even more stars and gas clouds. Light detected by NASA's Chandra X-ray Observatory is shown in blue and violet, indicating where gas is heated to millions of degrees by stellar explosions and by outflows from the supermassive black hole (image credits: NASA, ESA, SSC, CXC, STScI)
- The flares are due to the temporary but intense acceleration of particles around the black hole to much higher energies, with corresponding light emission. A huge advantage to observing Sgr A* with Webb is the capability of capturing data in two infrared wavelengths (F210M and F480M) simultaneously and continuously, from the telescope's location beyond the Moon. Webb will have an uninterrupted view, observing cycles of flaring and calm that the EHT team can use for reference with their own data, resulting in a cleaner image.
- The source or mechanism that causes Sgr A*'s flares is highly debated. Answers as to how Sgr A*'s flares begin, peak, and dissipate could have far-reaching implications for the future study of black holes, as well as particle and plasma physics, and even flares from the Sun.
- "Black holes are just cool," said Sera Markoff, an astronomer on the Webb Sgr A* research team and currently vice chairperson of EHT's Science Council. "The reason that scientists and space agencies across the world put so much effort into studying black holes is because they are the most extreme environments in the known universe, where we can put our fundamental theories, like general relativity, to a practical test."
- Black holes, predicted by Albert Einstein as part of his general theory of relativity, are in a sense the opposite of what their name implies—rather than an empty hole in space, black holes are the most dense, tightly-packed regions of matter known. A black hole's gravitational field is so strong that it warps the fabric of space around itself, and any material that gets too close is bound there forever, along with any light the material emits. This is why black holes appear "black." Any light detected by telescopes is not actually from the black hole itself, but the area surrounding it. Scientists call the ultimate inner edge of that light the event horizon, which is where the EHT collaboration gets its name.
- The EHT image of M87 was the first direct visual proof that Einstein's black hole prediction was correct. Black holes continue to be a proving ground for Einstein's theory, and scientists hope carefully scheduled multi-wavelength observations of Sgr A* by EHT, Webb, X-ray, and other observatories will narrow the margin of error on general relativity calculations, or perhaps point to new realms of physics we don't currently understand.
- As exciting as the prospect of new understanding and/or new physics may be, both Markoff and Zadeh noted that this is only the beginning. "It's a process. We will likely have more questions than answers at first," Markoff said. The Sgr A* research team plans to apply for more time with Webb in future years, to witness additional flaring events and build up a knowledge base, determining patterns from seemingly random flares. Knowledge gained from studying Sgr A* will then be applied to other black holes, to learn what is fundamental to their nature versus what makes one black hole unique.
- So the stressful scheduling Sudoku will continue for some time, but the astronomers agree it's worth the effort. "It's the noblest thing humans can do, searching for truth," Zadeh said. "It's in our nature. We want to know how the universe works, because we are part of the universe. Black holes could hold clues to some of these big questions."
- NASA's Webb telescope will serve as the premier space science observatory for the next decade and explore every phase of cosmic history—from within our solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries, and help humanity understand the origins of the universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• September 22, 2021: What was our Solar System like as it was forming billions of years ago? Over time, particles bumped into one another, building ever-larger rocks. Eventually, these rocks got big enough to form planets. We have some basic understanding of planet formation, but we don't know the details – especially details about the solar system's early chemical composition, and how it may have changed with time. And how did water make its way to Earth? While we can't time travel to get the answers, we can detail how other planetary systems are forming right now – and learn quite a lot. Researchers will train one of Webb's powerful instruments on the inner regions of 17 bright, actively forming planetary systems to begin to build an inventory of their contents. Element by element, they – along with researchers around the world – will be able to uncover what's present and how the disks' chemical makeup affects their contents, including planets that may be forming. 196)
- Planetary systems take millions of years to form, which introduces quite a challenge for astronomers. How do you identify which stage they are in, or categorize them? The best approach is to look at lots of examples and keep adding to the data we have – and NASA's upcoming James Webb Space Telescope will be able to provide an infrared inventory. Researchers using Webb will observe 17 actively forming planetary systems. These particular systems were previously surveyed by the Atacama Large Millimeter/submillimeter Array (ALMA), the largest radio telescope in the world, for the Disk Substructures at High Angular Resolution Project (DSHARP).
- Webb will measure spectra that can reveal molecules in the inner regions of these protoplanetary disks, complementing the details ALMA has provided about the disks' outer regions. These inner regions are where rocky, Earth-like planets can start to form, which is one reason why we want to know more about which molecules exist there.
- A research team led by Colette Salyk of Vassar College in Poughkeepsie, New York, and Klaus Pontoppidan of the Space Telescope Science Institute in Baltimore, Maryland, seek the details found in infrared light. "Once you switch to infrared light, specifically to Webb's range in mid-infrared light, we will be sensitive to the most abundant molecules that carry common elements," explained Pontoppidan.
Figure 140: The researchers will use NASA's James Webb Space Telescope to survey 17 of the 20 nearby protoplanetary disks observed by Chile's Atacama Large Millimeter/submillimeter Array (ALMA) in 2018 for its Disk Substructures at High Angular Resolution Project (DSHARP). ALMA delivered excellent data about the outer disks, but Webb will detail the inner disks by delivering spectra, which spread light out into a rainbow, revealing the chemical compositions of each object (image credit: Science: ALMA, ESO, NAOJ, NRAO, S. Andrews, Nicolas Lira)
- Researchers will be able to assess the quantities of water, carbon monoxide, carbon dioxide, methane, and ammonia – among many other molecules – in each disk. Critically, they will be able to count the molecules that contain elements essential to life as we know it, including oxygen, carbon, and nitrogen. How? With spectroscopy: Webb will capture all the light emitted at the center of each protoplanetary disk as a spectrum, which produces a detailed pattern of colors based on the wavelengths of light emitted. Since every molecule imprints a unique pattern on the spectrum, researchers can identify which molecules are there and build inventories of the contents within each protoplanetary disk. The strength of these patterns also carries information about the temperature and quantity of each molecule.
- "Webb's data will also help us identify where the molecules are within the overall system," Salyk said. "If they're hot, that implies they are closer to the star. If they're cooler, they may be farther away." This spatial information will help inform models that scientists build as they continue examining this program's data.
- Knowing what's in the inner regions of the disks has other benefits as well. Has water, for example, made it to this area, where habitable planets may be forming? "One of the things that's really amazing about planets – change the chemistry just a little bit and you can get these dramatically different worlds," Salyk continued. "That's why we're interested in the chemistry. We're trying to figure out how the materials initially found in a system may end up as different types of planets."
- If this sounds like a significant undertaking, do not worry – it will be a community effort. This is a Webb Treasury Program, which means that the data is released as soon as it's taken to all astronomers, allowing everyone to immediately pull the data, begin assessing what's what in each disk, and share their findings.
- "Webb's infrared data will be intensively studied," added co-investigator Ke Zhang of the University of Wisconsin–Madison. "We want the whole research community to be able to approach the data from different angles."
Why the Up-Close Examination?
- Let's step back, to see the forest for the trees. Imagine you are on a research boat off the coast of a distant terrain. This is the broadest view. If you were to land and disembark, you could begin counting how many trees there are and how many of each tree species. You could start identifying specific insects and birds and match up the sounds you heard offshore to the calls you hear under the treetops. This detailed cataloging is very similar to what Webb will empower researchers to do – but swap trees and animals for chemical elements.
- The protoplanetary disks in this program are very bright and relatively close to Earth, making them excellent targets to study. It's why they were surveyed by ALMA. It's also why researchers studied them with NASA's Spitzer Space Telescope. These objects have only been studied in depth since 2003, making this a relatively newer field of research. There's a lot Webb can add to what we know.
- The telescope's Mid-Infrared Instrument (MIRI) provides many advantages. Webb's location in space means that it can capture the full range of mid-infrared light (Earth's atmosphere filters it out). Plus, its data will have high resolution, which will reveal many more lines and wiggles in the spectra that the researchers can use to tease out specific molecules.
- The researchers were also selective about the types of stars chosen for these observations. This sample includes stars that are about half the mass of the Sun to about twice the mass of the Sun. Why? The goal is to help researchers learn more about systems that may be like our own as it formed. "With this sample, we can start to determine if there are any common features between the disks' properties and their inner chemistry," Zhang continued. "Eventually, we want to be able to predict which types of systems are more likely to generate habitable planets."
Figure 141: The MIRI of Webb will deliver incredibly rich information about the molecules that are present in the inner disks of still-forming planetary systems (known as protoplanetary disks). This simulated spectrum, which produces a detailed pattern of colors based on the wavelengths of light emitted, helps researchers take inventories of each molecule. This spectrum shows how much of the gasses like methane, ammonia, and carbon dioxide exist. Most of the unidentified features are water. Since spectra are teeming with details, they will help astronomers draw conclusions about the system's contents as planets form (image credit: Science: NASA, ESA, CSA, Artwork: Leah Hustak)
Beginning to Answer Big Questions
- This program may also help researchers begin to answer some classic questions: Are the forms taken by some of the most abundant elements found in protoplanetary disks, like carbon, nitrogen, and oxygen, "inherited" from the interstellar clouds that formed them? Or does the precise mix of chemicals change over time? "We think we can get to some of those answers by making inventories with Webb," Pontoppidan explained. "It's obviously a tremendous amount of work to do – and cannot be done only with these data – but I think we are going to make some major progress."
- Thinking even more broadly about the incredibly rich spectra Webb will provide, Salyk added, "I'm hoping that we'll see things that surprise us and then begin to study those serendipitous discoveries."
- This research will be conducted as part of Webb General Observer (GO) programs, which are competitively selected using a dual-anonymous review system, the same system that is used to allocate time on the Hubble Space Telescope.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• August 18, 2021: Peering deeply into a huge patch of sky the size of three full Moons, NASA's James Webb Space Telescope will undertake an ambitious program to study half a million galaxies. Called COSMOS-Webb, this survey is the largest project Webb will undertake during its first year. With more than 200 hours of observing time, it will build upon previous discoveries to make advances in three particular areas of study. These include revolutionizing our understanding of the Reionization Era; looking for early, fully evolved galaxies; and learning how dark matter evolved with galaxies' stellar content. With its rapid public release of the data, this survey will be a primary legacy dataset from Webb for scientists worldwide studying galaxies beyond the Milky Way. 197)
- When NASA's James Webb Space Telescope begins science operations in 2022, one of its first tasks will be an ambitious program to map the earliest structures in the universe. Called COSMOS-Webb, this wide and deep survey of half-a-million galaxies is the largest project Webb will undertake during its first year.
- With more than 200 hours of observing time, COSMOS-Webb will survey a large patch of the sky—0.6 square degrees—with the Near-Infrared Camera (NIRCam). That's the size of three full moons. It will simultaneously map a smaller area with the Mid-Infrared Instrument (MIRI).
- "It's a large chunk of sky, which is pretty unique to the COSMOS-Webb program. Most Webb programs are drilling very deep, like pencil-beam surveys that are studying tiny patches of sky," explained Caitlin Casey, an assistant professor at the University of Texas at Austin and co-leader of the COSMOS-Webb program. "Because we're covering such a large area, we can look at large-scale structures at the dawn of galaxy formation. We will also look for some of the rarest galaxies that existed early on, as well as map the large-scale dark matter distribution of galaxies out to very early times."
- (Dark matter does not absorb, reflect, or emit light, so it cannot be seen directly. We know that dark matter exists because of the effect it has on objects that we can observe.)
- COSMOS-Webb will study half-a-million galaxies with multi-band, high-resolution, near-infrared imaging , and an unprecedented 32,000 galaxies in the mid-infrared . With its rapid public release of the data, this survey will be a primary legacy dataset from Webb for scientists worldwide studying galaxies beyond the Milky Way.
Figure 142: This sea of galaxies is the complete, original COSMOS field from the Hubble Space Telescope's Advanced Camera for Surveys (ACS). The full mosaic is a composite of 575 separate ACS images, where each ACS image is about one-tenth the diameter of the full Moon. The jagged edges of the outline are due to the separate images that make up the survey field [credits: Science: NASA, ESA, Anton M. Koekemoer (STScI), Nick Scoville (Caltech)]
Building on Hubble's Achievements
- The COSMOS survey began in 2002 as a Hubble program to image a much larger patch of sky, about the area of 10 full moons. From there, the collaboration snowballed to include most of the world's major telescopes on Earth and in space. Now COSMOS is a multi-wavelength survey that covers the entire spectrum from the X-ray through the radio.
- Because of its location on the sky, the COSMOS field is accessible to observatories around the world. Located on the celestial equator , it can be studied from both the northern and southern hemispheres, resulting in a rich and diverse treasury of data.
- "COSMOS has become the survey that a lot of extragalactic scientists go to in order to conduct their analyses because the data products are so widely available, and because it covers such a wide area of the sky," said Rochester Institute of Technology's Jeyhan Kartaltepe, assistant professor of physics and co-leader of the COSMOS-Webb program. "COSMOS-Webb is the next installment of that, where we're using Webb to extend our coverage in the near- and mid-infrared part of the spectrum, and therefore pushing out our horizon, how far away we're able to see."
- The ambitious COSMOS-Webb program will build upon previous discoveries to make advances in three particular areas of study, including: revolutionizing our understanding of the Reionization Era; looking for early, fully evolved galaxies; and learning how dark matter evolved with galaxies' stellar content.
Goal 1: Revolutionizing Our Understanding of the Reionization Era
- Soon after the big bang, the universe was completely dark. Stars and galaxies, which bathe the cosmos in light, had not yet formed. Instead, the universe consisted of a primordial soup of neutral hydrogen and helium atoms and invisible dark matter. This is called the cosmic dark ages.
- After several hundred million years, the first stars and galaxies emerged and provided energy to reionize the early universe. This energy ripped apart the hydrogen atoms that filled the universe, giving them an electric charge and ending the cosmic dark ages. This new era where the universe was flooded with light is called the Reionization Era.
- The first goal of COSMOS-Webb focuses on this epoch of reionization, which took place from 400,000 to 1 billion years after the big bang. Reionization likely happened in little pockets, not all at once. COSMOS-Webb will look for bubbles showing where the first pockets of the early universe were reionized. The team aims to map the scale of these reionization bubbles.
- "Hubble has done a great job of finding handfuls of these galaxies out to early times, but we need thousands more galaxies to understand the reionization process," explained Casey.
- Scientists don't even know what kind of galaxies ushered in the Reionization Era, whether they're very massive or relatively low-mass systems. COSMOS-Webb will have a unique ability to find very massive, rare galaxies and see what their distribution is like in large-scale structures. So, are the galaxies responsible for reionization living in the equivalent of a cosmic metropolis, or are they mostly evenly distributed across space? Only a survey the size of COSMOS-Webb can help scientists to answer this.
Goal 2: Looking for Early, Fully Evolved Galaxies
- COSMOS-Webb will search for very early, fully evolved galaxies that shut down star birth in the first 2 billion years after the big bang. Hubble has found a handful of these galaxies, which challenge existing models about how the universe formed. Scientists struggle to explain how these galaxies could have old stars and not be forming any new stars so early in the history of the universe.
- With a large survey like COSMOS-Webb, the team will find many of these rare galaxies. They plan detailed studies of these galaxies to understand how they could have evolved so rapidly and turned off star formation so early.
Goal 3: Learning How Dark Matter Evolved with Galaxies' Stellar Content
- COSMOS-Webb will give scientists insight into how dark matter in galaxies has evolved with the galaxies' stellar content over the universe's lifetime.
- Galaxies are made of two types of matter: normal, luminous matter that we see in stars and other objects, and invisible dark matter, which is often more massive than the galaxy and can surround it in an extended halo. Those two kinds of matter are intertwined in galaxy formation and evolution. However, presently there's not much knowledge about how the dark matter mass in the halos of galaxies formed, and how that dark matter impacts the formation of the galaxies.
- COSMOS-Webb will shed light on this process by allowing scientists to directly measure these dark matter halos through "weak lensing." The gravity from any type of mass—whether it's dark or luminous—can serve as a lens to "bend" the light we see from more distant galaxies. Weak lensing distorts the apparent shape of background galaxies, so when a halo is located in front of other galaxies, scientists can directly measure the mass of the halo's dark matter.
- "For the first time, we'll be able to measure the relationship between the dark matter mass and the luminous mass of galaxies back to the first 2 billion years of cosmic time," said team member Anton Koekemoer, a research astronomer at the Space Telescope Science Institute in Baltimore, who helped design the program's observing strategy and is in charge of constructing all the images from the program. "That's a crucial epoch for us to try to understand how the galaxies' mass was first put in place, and how that's driven by the dark matter halos. And that can then feed indirectly into our understanding of galaxy formation."
Quickly Sharing Data with the Community
- COSMOS-Webb is a Treasury program, which by definition is designed to create datasets of lasting scientific value. Treasury Programs strive to solve multiple scientific problems with a single, coherent dataset. Data taken under a Treasury Program usually has no exclusive access period, enabling immediate analysis by other researchers.
- "As a Treasury Program, you are committing to quickly releasing your data and your data products to the community," explained Kartaltepe. "We're going to produce this community resource and make it publicly available so that the rest of the community can use it in their scientific analyses."
- Koekemoer added, "A Treasury Program commits to making publicly available all these science products so that anyone in the community, even at very small institutions, can have the same, equal access to the data products and then just do the science."
- COSMOS-Webb is a Cycle 1 General Observers program. General Observers programs were competitively selected using a dual-anonymous review system, the same system that is used to allocate time on Hubble.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• July 21, 2021: Researchers will use NASA's upcoming James Webb Space Telescope to study Beta Pictoris, an intriguing young planetary system that sports at least two planets, a jumble of smaller, rocky bodies, and a dusty disk. Their goals include gaining a better understanding of the structures and properties of the dust to better interpret what is happening in the system. Since it's only about 63 light-years away and chock full of dust, it appears bright in infrared light – and that means there is a lot of information for Webb to gather. 198)
- Beta Pictoris is the target of several planned Webb observing programs, including one led by Chris Stark of NASA's Goddard Space Flight Center in Greenbelt, Maryland, and two led by Christine Chen of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. Stark's program will directly image the system after blocking the light of the star to gather a slew of new details about its dust. Chen's programs will gather spectra, which spread light out like a rainbow to reveal which elements are present. All three observing programs will add critical details to what's known about this nearby system.
First, a Review of What We Know
- Beta Pictoris has been regularly studied in radio, infrared, and visible light since the 1980s. The star itself is twice as massive as our sun and quite a bit hotter, but also significantly younger. (The Sun is 4.6 billion years old, but Beta Pictoris is approximately 20 million years old.) At this stage, the star is stable and hosts at least two planets, which are both far more massive than Jupiter. But this planetary system is remarkable because it is where the first exocomets (comets in other systems) were discovered. There are quite a lot of bodies zipping around this system!
- Like our own solar system, Beta Pictoris has a debris disk, which includes comets, asteroids, rocks of various sizes, and plenty of dust in all shapes that orbit the star. (A debris disk is far younger and can be more massive than our solar system's Kuiper Belt, which begins near Neptune's orbit and is where many short-period comets originate.)
- This outside ring of dust and debris is also where a lot of activity is happening. Pebbles and boulders could be colliding and breaking into far smaller pieces — sending out plenty of dust.
Figure 143: A debris disk, which includes comets, asteroids, rocks of various sizes, and plenty of dust, orbits the star Beta Pictoris, which is blocked at the center of this 2012 image by a coronagraph aboard the Hubble Space Telescope. This is the visible-light view of the system. NASA's James Webb Space Telescope will view Beta Pictoris in infrared light, both using its coronagraphs and capturing data known as spectra to allow researchers to learn significantly more about the gas and dust in the debris disk, which includes lots of smaller bodies like exocomets [image credit: NASA, ESA, Daniel Apai (University of Arizona), Glenn Schneider (University of Arizona)]
Scrutinizing This Planetary System
- Stark's team will use Webb's coronagraphs, which block the light of the star, to observe the faint portions of the debris disk that surround the entire system. "We know there are two massive planets around Beta Pictoris, and farther out there is a belt of small bodies that are colliding and fragmenting," Stark explained. "But what's in between? How similar is this system to our solar system? Can dust and water ice from the outer belt eventually make its way into the inner region of the system? Those are details we can help tease out with Webb."
- Webb's imagery will allow the researchers to study how the small dust grains interact with planets that are present in that system. Plus, Webb will detail all the fine dust that streams off these objects, permitting the researchers to infer the presence of larger rocky bodies and what their distribution is in the system. They'll also carefully assess how the dust scatters light and reabsorbs and reemits light when it's warm, allowing them to constrain what the dust is made of. By cataloging the specifics of Beta Pictoris, the researchers will also assess how similar this system is to our solar system, helping us understand if the contents of our solar system are unique.
- Isabel Rebollido, a team member and postdoctoral researcher at STScI, is already building complex models of Beta Pictoris. The first model combines existing data about the system, including radio, near-infrared, far-infrared, and visible light from both space- and ground-based observatories. In time, she will add Webb's imagery to run a fuller analysis.
- The second model will feature only Webb's data – and will be the first they explore. "Is the light Webb will observe symmetrical?" Rebollido asked. "Or are there 'bumps' of light here and there because there is an accumulation of dust? Webb is far more sensitive than any other space telescope and gives us a chance to look for this evidence, as well as water vapor where we know there's gas."
Dust as a Decoder Ring
- Think of the debris disk of Beta Pictoris as a very busy, elliptical highway – except one where there aren't many traffic rules. Collisions between comets and larger rocks can produce fine dust particles that subsequently scatter throughout the system.
- "After planets, most of the mass in the Beta Pictoris system is thought to be in smaller planetesimals that we can't directly observe," Chen explained. "Fortunately, we can observe the dust left behind when planetesimals collide."
- This dust is where Chen's team will focus its research. What do the smallest dust grains look like? Are they compact or fluffy? What are they made of?
- "We'll analyze Webb's spectra to map the locations of dust and gas – and figure out what their detailed compositions are," Chen explained. "Dust grains are 'fingerprints' of planetesimals we can't see directly and can tell us about what these planetesimals are made of and how they formed." For example, are the planetesimals ice-rich like comets in our solar system? Are there signs of high-speed collisions between rocky planetesimals? Clearly analyzing if grains in one region are more solid or fluffy than another will help the researchers understand what is happening to the dust, and map out the subtle differences in the dust in each region.
- "I'm looking forward to analyzing Webb's data since it will provide exquisite detail," added Cicero X. Lu, a team member and a fourth-year Ph.D. student at Johns Hopkins University in Baltimore. "Webb will allow us to identify more elements and pinpoint their precise structures."
- In particular, there's a cloud of carbon monoxide at the edge of the disk that greatly interests these researchers. It's asymmetric and has an irregular, blobby side. One theory is that collisions released dust and gas from larger, icy bodies to form this cloud. Webb's spectra will help them build scenarios that explain its origin.
The Reach of Infrared
- These research programs are only possible because Webb has been designed to provide crisp, high-resolution detail in infrared light. The observatory specializes in collecting infrared light – which travels through gas and dust – both with images and spectra. Webb also has another advantage – its position in space. Webb will not be hindered by Earth's atmosphere, which filters out some types of light, including several infrared wavelength bands. This observatory will allow researchers to gather a more complete range of infrared light and data about Beta Pictoris for the first time.
- These studies will be conducted as part of Webb Guaranteed Time Observations (GTO) and General Observers (GO) programs. The GTO programs are led by scientists who helped develop the key hardware and software components or technical and inter-disciplinary knowledge for the observatory. GO programs are competitively selected using a dual-anonymous review system, the same system that is used to allocate time on the Hubble Space Telescope.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• June 23, 2021: Looking back in time, Webb will see quasars as they appeared billions of years ago. Outshining all the stars in their host galaxies combined, quasars are among the brightest objects in the universe. These brilliant, distant and active supermassive black holes shape the galaxies in which they reside. Shortly after its launch, scientists will use Webb to study six of the most far-flung and luminous quasars, along with their host galaxies, in the very young universe. They will examine what part quasars play in galaxy evolution during these early times. The team will also use the quasars to study the gas in the space between galaxies in the infant universe. Only with Webb's extreme sensitivity to low levels of light and its superb angular resolution will this be possible. 199)
- Quasars are very bright, distant and active supermassive black holes that are millions to billions of times the mass of the Sun. Typically located at the centers of galaxies, they feed on infalling matter and unleash fantastic torrents of radiation. Among the brightest objects in the universe, a quasar's light outshines that of all the stars in its host galaxy combined, and its jets and winds shape the galaxy in which it resides.
- Shortly after its launch later this year, a team of scientists will train NASA's James Webb Space Telescope on six of the most distant and luminous quasars. They will study the properties of these quasars and their host galaxies, and how they are interconnected during the first stages of galaxy evolution in the very early universe. The team will also use the quasars to examine the gas in the space between galaxies, particularly during the period of cosmic reionization , which ended when the universe was very young. They will accomplish this using Webb's extreme sensitivity to low levels of light and its superb angular resolution.
Figure 144: Quasar Outflow Illustration. This is an artist's concept of a galaxy with a brilliant quasar at its center. A quasar is a very bright, distant and active supermassive black hole that is millions to billions of times the mass of the Sun. Among the brightest objects in the universe, a quasar's light outshines that of all the stars in its host galaxy combined. Quasars feed on infalling matter and unleash torrents of winds and radiation, shaping the galaxies in which they reside. Using the unique capabilities of Webb, scientists will study six of the most distant and luminous quasars in the universe [image credit: ARTWORK: NASA, ESA, Joseph Olmsted (STScI)]
Webb: Visiting the Young Universe
- As Webb peers deep into the universe, it will actually look back in time. Light from these distant quasars began its journey to Webb when the universe was very young and took billions of years to arrive. We will see things as they were long ago, not as they are today.
- "All these quasars we are studying existed very early, when the universe was less than 800 million years old, or less than 6 percent of its current age. So these observations give us the opportunity to study galaxy evolution and supermassive black hole formation and evolution at these very early times," explained team member Santiago Arribas, a research professor at the Department of Astrophysics of the Center for Astrobiology in Madrid, Spain. Arribas is also a member of Webb's Near-Infrared Spectrograph (NIRSpec) Instrument Science Team.
- The light from these very distant objects has been stretched by the expansion of space. This is known as cosmological redshift . The farther the light has to travel, the more it is redshifted. In fact, the visible light emitted at the early universe is stretched so dramatically that it is shifted out into the infrared when it arrives to us. With its suite of infrared-tuned instruments, Webb is uniquely suited to studying this kind of light.
Studying Quasars, Their Host Galaxies and Environments, and Their Powerful Outflows
- The quasars the team will study are not only among the most distant in the universe, but also among the brightest. These quasars typically have the highest black hole masses, and they also have the highest accretion rates — the rates at which material falls into the black holes.
- "We're interested in observing the most luminous quasars because the very high amount of energy that they're generating down at their cores should lead to the largest impact on the host galaxy by the mechanisms such as quasar outflow and heating," said Chris Willott, a research scientist at the Herzberg Astronomy and Astrophysics Research Centre of the National Research Council of Canada (NRC) in Victoria, British Columbia. Willott is also the Canadian Space Agency's Webb project scientist. "We want to observe these quasars at the moment when they're having the largest impact on their host galaxies."
- An enormous amount of energy is liberated when matter is accreted by the supermassive black hole. This energy heats and pushes the surrounding gas outward, generating strong outflows that tear across interstellar space like a tsunami, wreaking havoc on the host galaxy.
- Outflows play an important role in galaxy evolution. Gas fuels the formation of stars, so when gas is removed due to outflows, the star-formation rate decreases. In some cases, outflows are so powerful and expel such large amounts of gas that they can completely halt star formation within the host galaxy. Scientists also think that outflows are the main mechanism by which gas, dust and elements are redistributed over large distances within the galaxy or can even be expelled into the space between galaxies – the intergalactic medium. This may provoke fundamental changes in the properties of both the host galaxy and the intergalactic medium.
Examining Properties of Intergalactic Space During the Era of Reionization
- More than 13 billion years ago, when the universe was very young, the view was far from clear. Neutral gas between galaxies made the universe opaque to some types of light. Over hundreds of millions of years, the neutral gas in the intergalactic medium became charged or ionized, making it transparent to ultraviolet light. This period is called the Era of Reionization. But what led to the reionization that created the "clear" conditions detected in much of the universe today? Webb will peer deep into space to gather more information about this major transition in the history of the universe. The observations will help us understand the Era of Reionization, which is one of the key frontiers in astrophysics.
- The team will use quasars as background light sources to study the gas between us and the quasar. That gas absorbs the quasar's light at specific wavelengths. Through a technique called imaging spectroscopy, they will look for absorption lines in the intervening gas. The brighter the quasar is, the stronger those absorption line features will be in the spectrum. By determining whether the gas is neutral or ionized, scientists will learn how neutral the universe is and how much of this reionization process has occurred at that particular point in time.
- "If you want to study the universe, you need very bright background sources. A quasar is the perfect object in the distant universe, because it's luminous enough that we can see it very well," said team member Camilla Pacifici, who is affiliated with the Canadian Space Agency but works as an instrument scientist at the Space Telescope Science Institute in Baltimore. "We want to study the early universe because the universe evolves, and we want to know how it got started."
- The team will analyze the light coming from the quasars with NIRSpec to look for what astronomers call "metals," which are elements heavier than hydrogen and helium. These elements were formed in the first stars and the first galaxies and expelled by outflows. The gas moves out of the galaxies it was originally in and into the intergalactic medium. The team plans to measure the generation of these first "metals," as well as the way they're being pushed out into the intergalactic medium by these early outflows.
The Power of Webb
- Webb is an extremely sensitive telescope able to detect very low levels of light. This is important, because even though the quasars are intrinsically very bright, the ones this team is going to observe are among the most distant objects in the universe. In fact, they are so distant that the signals Webb will receive are very, very low. Only with Webb's exquisite sensitivity can this science be accomplished. Webb also provides excellent angular resolution, making it possible to disentangle the light of the quasar from its host galaxy.
- The quasar programs described here are Guaranteed Time Observations involving the spectroscopic capabilities of NIRSpec.
- he James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• April 21, 2021: Although more than 4,000 planets have been discovered around other stars, they don't represent the wide diversity of possible alien worlds. Most of the exoplanets detected so far are so-called "star huggers": they orbit so close to their host stars that they complete an orbit in days or weeks. These are the easiest to find with current detection techniques. 200)
- But there's a vast, mostly uncharted landscape to hunt for exoplanets in more distant orbits. Astronomers have only begun to explore this frontier. The planets are far enough away from their stars that telescopes equipped with masks to block out a star's blinding glare can see the planets directly. The easiest planets to spot are hot, newly formed worlds. They are young enough that they still glow in infrared light with the heat from their formation.
- This outer realm of exoplanetary systems is an ideal hunting ground for NASA's upcoming James Webb Space Telescope. Webb will probe the atmospheres of nearby known exoplanets, such as HR 8799 and 51 Eridani b, at infrared wavelengths. Webb also will hunt for other distant worlds—possibly down to Saturn-size—on the outskirts of planetary systems that cannot be detected with ground-based telescopes.
- Before planets around other stars were first discovered in the 1990s, these far-flung exotic worlds lived only in the imagination of science fiction writers.
- But even their creative minds could not have conceived of the variety of worlds astronomers have uncovered. Many of these worlds, called exoplanets, are vastly different from our solar system's family of planets. They range from star-hugging "hot Jupiters" to oversized rocky planets dubbed "super Earths." Our universe apparently is stranger than fiction.
- That's why astronomers have identified most of the more than 4,000 exoplanets found so far using indirect techniques, such as through a star's slight wobble or its unexpected dimming as a planet passes in front of it, blocking some of the starlight.
- These techniques work best, however, for planets orbiting close to their stars, where astronomers can detect changes over weeks or even days as the planet completes its racetrack orbit. But finding only star-skimming planets doesn't provide astronomers with a comprehensive picture of all the possible worlds in star systems.
- Another technique researchers use in the hunt for exoplanets, which are planets orbiting other stars, is one that focuses on planets that are farther away from a star's blinding glare. Scientists, using specialized imaging techniques that block out the glare from the star, have uncovered young exoplanets that are so hot they glow in infrared light. In this way, some exoplanets can be directly seen and studied.
Figure 145: Left: This is an image of the star HR 8799 taken by Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) in 1998. A mask within the camera (coronagraph) blocks most of the light from the star. Astronomers also used software to digitally subtract more starlight. Nevertheless, scattered light from HR 8799 dominates the image, obscuring the four faint planets. The exoplanets were discovered in 2007, 2008, and 2010 in near-infrared ground-based images taken with the W.M. Keck Observatory in Hawaii and the Gemini North telescope in Chile. The system is 133 light-years from Earth.
Right: A re-analysis of NICMOS data in 2011 uncovered three of the exoplanets, which were not seen in the 1998 images. Sophisticated software processing of the NICMOS data removes most of the scattered starlight to reveal the three planets orbiting HR 8799. Astronomers used this decade-old image to calculate the planets' orbits. The fourth, innermost planet cannot be seen because it is on the edge of the NICMOS coronagraphic spot that blocks the light from the central star.
Webb will probe the planets' atmospheres at infrared wavelengths astronomers have rarely used to image distant worlds. Webb will also hunt for other distant worlds—possibly down to Saturn-size—on the outskirts of planetary systems that cannot be detected with ground-based telescopes [image credit: NASA, ESA, Rémi Soummer (STScI)]
- NASA's upcoming James Webb Space Telescope will help astronomers probe farther into this bold new frontier. Webb, like some ground-based telescopes, is equipped with special optical systems called coronagraphs, which use masks designed to block out as much starlight as possible to study faint exoplanets and to uncover new worlds.
- Two targets early in Webb's mission are the planetary systems 51 Eridani and HR 8799. Out of the few dozen directly imaged planets, astronomers plan to use Webb to analyze in detail the systems that are closest to Earth and have planets at the widest separations from their stars. This means that they appear far enough away from a star's glare to be directly observed. The HR 8799 system resides 133 light-years and 51 Eridani 96 light-years from Earth.
Webb's Planetary Targets
- Two observing programs early in Webb's mission combine the spectroscopic capabilities of the Near Infrared Spectrograph (NIRSpec) and the imaging of the Near Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI ) to study the four giant planets in the HR 8799 system. In a third program, researchers will use NIRCam to analyze the giant planet in 51 Eridani.
- The four giant planets in the HR 8799 system are each roughly 10 Jupiter masses. They orbit more than 14 billion miles from a star that is slightly more massive than the Sun. The giant planet in 51 Eridani is twice the mass of Jupiter and orbits about 11 billion miles from a Sun-like star. Both planetary systems have orbits oriented face-on toward Earth. This orientation gives astronomers a unique opportunity to get a bird's-eye view down on top of the systems, like looking at the concentric rings on an archery target.
- Many exoplanets found in the outer orbits of their stars are vastly different from our solar system planets. Most of the exoplanets discovered in this outer region, including those in HR 8799, are between 5 and 10 Jupiter masses, making them the most massive planets ever found to date.
- These outer exoplanets are relatively young, from tens of millions to hundreds of millions of years old—much younger than our solar system's 4.5 billion years. So they're still glowing with heat from their formation. The images of these exoplanets are essentially baby pictures, revealing planets in their youth.
- Webb will probe into the mid-infrared, a wavelength range astronomers have rarely used before to image distant worlds. This infrared "window" is difficult to observe from the ground because of thermal emission from—and absorption in—Earth's atmosphere.
- "Webb's strong point is the uninhibited light coming through space in the mid-infrared range," said Klaus Hodapp of the University of Hawaii in Hilo, lead investigator of the NIRSpec observations of the HR 8799 system. "Earth's atmosphere is pretty difficult to work through. The major absorption molecules in our own atmosphere prevent us from seeing interesting features in planets."
- The mid-infrared "is the region where Webb really will make seminal contributions to understanding what are the particular molecules, what are the properties of the atmosphere that we hope to find which we don't really get just from the shorter, near-infrared wavelengths," said Charles Beichman of NASA's Jet Propulsion Laboratory in Pasadena, California, lead investigator of the NIRCam and MIRI observations of the HR 8799 system. "We'll build on what the ground-based observatories have done, but the goal is to expand on that in a way that would be impossible without Webb."
How Do Planets Form?
- One of the researchers' main goals in both systems is to use Webb to help determine how the exoplanets formed. Were they created through a buildup of material in the disk surrounding the star, enriched in heavy elements such as carbon, just as Jupiter probably did? Or, did they form from the collapse of a hydrogen cloud, like a star, and become smaller under the relentless pull of gravity?
- Atmospheric makeup can provide clues to a planet's birth. "One of the things we'd like to understand is the ratio of the elements that have gone into the formation of these planets," Beichman said. "In particular, carbon versus oxygen tells you quite a lot about where the gas that formed the planet comes from. Did it come from a disk that accreted a lot of the heavier elements or did it come from the interstellar medium ? So it's what we call the carbon-to-oxygen ratio that is quite indicative of formation mechanisms."
- To answer these questions, the researchers will use Webb to probe deeper into the exoplanets' atmospheres. NIRCam, for example, will measure the atmospheric fingerprints of elements like methane. It also will look at cloud features and the temperatures of these planets. "We already have a lot of information at these near-infrared wavelengths from ground-based facilities," said Marshall Perrin of the Space Telescope Science Institute in Baltimore, Maryland, lead investigator of NIRCam observations of 51 Eridani b. "But the data from Webb will be much more precise, much more sensitive. We'll have a more complete set of wavelengths, including filling in gaps where you can't get those wavelengths from the ground."
- The astronomers will also use Webb and its superb sensitivity to hunt for less-massive planets far from their star. "From ground-based observations, we know that these massive planets are relatively rare," Perrin said. "But we also know that for the inner parts of systems, lower-mass planets are dramatically more common than larger-mass planets. So the question is, does it also hold true for these further separations out?" Beichman added, "Webb's operation in the cold environment of space allows a search for fainter, smaller planets, impossible to detect from the ground."
- Another goal is understanding how the myriad planetary systems discovered so far were created.
- "I think what we are finding is that there is a huge diversity in solar systems," Perrin said. "You have systems where you have these hot Jupiter planets in very close orbits. You have systems where you don't. You have systems where you have a 10-Jupiter-mass planet and ones in which you have nothing more massive than several Earths. We ultimately want to understand how the diversity of planetary system formation depends on the environment of the star, the mass of the star, all sorts of other things and eventually through these population-level studies, we hope to place our own solar system in context."
- The NIRSpec spectroscopic observations of HR 8799 and the NIRCam observations of 51 Eridani are part of the Guaranteed Time Observations programs that will be conducted shortly after Webb's launch later this year. The NIRCam and MIRI observations of HR 8799 is a collaboration of two instrument teams and is also part of the Guaranteed Time Observations program.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• March 17, 2021: As technology has improved over the centuries, so have astronomers' observations of nearby galaxy Centaurus A. They have peeled back its layers like an onion to discover that its wobbly shape is the result of two galaxies that merged more than 100 million years ago. It also has an active supermassive black hole, known as an active galactic nucleus, at its heart that periodically sends out twin jets. Despite these advancements, Centaurus A's dusty core is still quite mysterious. Webb's high-resolution infrared data will allow a research team to very precisely reveal all that lies at the center. 201)
- Centaurus A is a giant of a galaxy, but its appearances in telescope observations can be deceiving. Dark dust lanes and young blue star clusters, which crisscross its central region, are apparent in ultraviolet, visible, and near-infrared light, painting a fairly subdued landscape. But by switching to X-ray and radio light views, a far more raucous scene begins to unfold: From the core of the misshapen elliptical galaxy, spectacular jets of material have erupted from its active supermassive black hole – known as an active galactic nucleus – sending material into space well beyond the galaxy's limits.
- What, precisely, is happening at its core to cause all this activity? Upcoming observations led by Nora Lützgendorf and Macarena García Marín of the European Space Agency using NASA's James Webb Space Telescope will allow researchers to peer through its dusty core in high resolution for the first time to begin to answer these questions.
- "There's so much going on in Centaurus A," explains Lützgendorf. "The galaxy's gas, disk, and stars all move under the influence of its central supermassive black hole. Since the galaxy is so close to us, we'll be able to use Webb to create two-dimensional maps to see how the gas and stars move in its central region, how they are influenced by the jets from its active galactic nucleus, and ultimately better characterize the mass of its black hole."
Figure 146: Centaurus A sports a warped central disk of gas and dust, which is evidence of a past collision and merger with another galaxy. It also has an active galactic nucleus that periodically emits jets. It is the fifth brightest galaxy in the sky and only about 13 million light-years away from Earth, making it an ideal target to study an active galactic nucleus – a supermassive black hole emitting jets and winds – with NASA's upcoming James Webb Space Telescope [image credit: X-ray: NASA/CXC/SAO; Optical: Rolf Olsen; Infrared: NASA /JPL-Caltech; Radio: NRAO/AUI/NSF/Univ.Hertfordshire/M.Hardcastle]
A Quick Look Back
- Let's hit "rewind" to review a bit of what is already known about Centaurus A. It's well studied because it's relatively nearby – about 13 million light-years away – which means we can clearly resolve the full galaxy. The first record of it was logged in the mid-1800s, but astronomers lost interest until the 1950s because the galaxy appeared to be a quiet, if misshapen, elliptical galaxy. Once researchers were able to begin observing with radio telescopes in the 1940s and '50s, Centaurus A became radically more interesting – and its jets came into view. In 1954, researchers found that Centaurus A is the result of two galaxies that merged, which was later estimated to have occurred 100 million years ago.
- With more observations in the early 2000s, researchers estimated that about 10 million years ago, its active galactic nucleus shot out twin jets in opposite directions. When examined across the electromagnetic spectrum, from X-ray to radio light, it's clear there is far more to this story that we still have to learn.
- "Multi-wavelength studies of any galaxy are like the layers of an onion. Each wavelength shows you something different," said Marín. "With Webb's near- and mid-infrared instruments, we'll see far colder gas and dust than in previous observations, and learn much more about the environment at the center of the galaxy."
Visualizing Webb's Data
- The team led by Lützgendorf and Marín will observe Centaurus A not only by taking images with Webb, but by gathering data known as spectra, which spread out light into its component wavelengths like a rainbow. Webb's spectra will reveal high-resolution information about the temperatures, speeds, and compositions of the material at the center of the galaxy.
- In particular, Webb's Near Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) will provide the research team with a combination of data: an image plus a spectrum from within each pixel of that image. This will allow the researchers to build intricate 2D maps from the spectra that will help them identify what's happening behind the veil of dust at the center – and analyze it from many angles in depth.
- Compare this style of modeling to the analysis of a garden. In the same way botanists classify plants based on specific sets of features, these researchers will classify spectra from Webb's MIRI to construct "gardens" or models. "If you take a snapshot of a garden from a great distance away," Marín explained, "You will see something green, but with Webb, we will be able to see individual leaves and flowers, their stems, and maybe the soil underneath."
- As the research team digs into the spectra, they'll build maps from individual parts of the garden, comparing one spectrum to another nearby spectrum. This is analogous to determining which parts contain which plant species based on comparisons of "stems," "leaves," and "flowers" as they go.
- "When it comes to spectral analysis, we conduct many comparisons," Marín continued. "If I compare two spectra in this region, maybe I will find that what was observed contains a prominent population of young stars. Or confirm which areas are both dusty and heated. Or maybe we will identify emission coming from the active galactic nucleus."
- In other words, the "ecosystem" of spectra has many levels, which will allow the team to better define precisely what is present and where it is – which is made possible by Webb's specialized infrared instruments. And, since these studies will build on many that came before, the researchers will be able to confirm, refine, or break new ground by identifying new features.
Figure 147: Centaurus A's dusty core is apparent in visible light, but its jets are best viewed in X-ray and radio light. With upcoming observations from NASA's James Webb Space Telescope in infrared light, researchers hope to better pinpoint the mass of the galaxy's central supermassive black hole as well as evidence that shows where the jets were ejected [image credit: X-ray: NASA/CXC/SAO; Optical: Rolf Olsen; Infrared: NASA/JPL-Caltech; Radio: NRAO/AUI/NSF/Univ.Hertfordshire/M.Hardcastle]
Weighing the Black Hole in Centaurus A
- The combination of images and spectra provided by NIRSpec and MIRI will allow the team to create very high-resolution maps of the speeds of the gas and stars at the center of Centaurus A. "We plan to use these maps to model how the entire disk at the center of the galaxy moves to more precisely determine the black hole's mass," Lützgendorf explains.
- Since researchers understand how the gravity of a black hole governs the rotation of nearby gas, they can use the Webb data to weigh the black hole in Centaurus A. With a more complete set of infrared data, they will also determine if different parts of the gas are all behaving as anticipated. "I'm looking forward to fully filling out our data," Lützgendorf said. "I hope to see how the ionized gas behaves and twirls, and where we see the jets."
- The researchers are also hoping to break new ground. "It's possible we'll find things we haven't considered yet," Lützgendorf explains. "In some aspects, we'll be covering completely new territory with Webb." Marín wholeheartedly agrees, and adds that building on a wealth of existing data is invaluable. "The most exciting aspects about these observations is the potential for new discoveries," she said. "I think we might find something that makes us look back to other data and reinterpret what was seen earlier."
- These studies of Centaurus A will be conducted as part of Gillian Wright and Pierre Ferruit's joint MIRI and NIRSpec Guaranteed Time Observations programs. All of Webb's data will ultimately be stored in the publicly accessible Barbara A. Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute in Baltimore.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• February 22, 2021: Early observations of stars in the local universe will pave the way for years of discovery across a range of science topics. 202)
- The combination of high resolution and infrared-detecting instruments on NASA's upcoming James Webb Space Telescope will reveal stars that are currently hidden even from the powerful Hubble Space Telescope. The wealth of additional star data will allow astronomers to investigate a range of questions, from star birth to star death, to the universe's elusive expansion rate. Early observations with Webb will demonstrate its ability to distinguish the individual light of stars in the local universe in a range of environments and provide astronomers with tools for making the most of Webb's powerful capabilities.
- "NASA's Hubble and Spitzer space telescopes have been transformative, opening the door to the infrared universe, beyond the realm of red visible light. Webb is a natural evolution of those missions, combining Spitzer's view of the infrared universe with Hubble's sensitivity and resolution," says Daniel Weisz of the University of California, Berkeley, the principal investigator on Webb's early release science (ERS) program on resolved populations of stars.
- Webb's ability to resolve individual stars that are shrouded behind gas and dust in visible light will be applicable to many areas of astronomical research. The goals of this ERS program are to demonstrate Webb's capabilities in the local universe and create free, open-source data analysis programs for astronomers to make the best use of the observatory as quickly as possible. Data from the ERS programs will be available to other astronomers immediately, and archived for future research via the Barbara A. Mikulski Archive for Space Telescopes (MAST).
Figure 148: This image from NASA's Hubble Space Telescope shows the heart of the globular star cluster Messier 92 (M92), one of the oldest and brightest in the Milky Way. The cluster packs roughly 330,000 stars tightly together, and they orbit the center of the galaxy en masse. NASA's James Webb Space Telescope will observe M92, or a similar globular cluster, early in its mission to demonstrate its ability to distinguish the light of its individual stars in a densely packed environment. Webb's high resolution and sensitivity will provide scientists a wealth of detailed star data relevant to many areas of astronomy, including the stellar lifecycle and the evolution of the universe (image credit: NASA, ESA, and Gilles Chapdelaine)
Insight into Dark Energy
- Webb's ability to pick out details for more individual stars than we have seen before will improve distance measurements to nearby galaxies, which Weisz says will be crucial to one of the biggest mysteries of modern-day astronomy: How fast is the universe expanding? A phenomenon called dark energy seems to be driving this expansion. Various methods for calculating the expansion rate have resulted in different answers—discrepancies astronomers hope Webb's data can help reconcile.
- "In order to do any of this science, calculating distances and then the universe's expansion rate, we need to be able to extract the light of individual stars from Webb images," Weisz says. "Our ERS program team will develop software that empowers the community to make those types of measurements."
The Stellar Lifecycle
- Seeing more stars will mean more insight into their lifecycle. Webb will provide new views of the full range of stages in a star's life, from formation to death.
- "Right now we are effectively limited to studying star formation in our own Milky Way galaxy, but with Webb's infrared capabilities we can see through the dusty cocoons that shelter forming protostars in other galaxies—like Andromeda, which is more metal-rich—and see how stars form in a very different environment," Weisz says.
- Astronomer Martha Boyer, also on this observing-program team, is interested in the insights Webb will provide toward the end of the stellar lifecycle, when stars become bloated, red, and dusty.
- "NASA's Spitzer Space Telescope showed us that dusty, evolved stars exist even in very primitive galaxies where they weren't expected, and now with Webb we will be able to characterize them and learn how our models of the star lifecycle line up with real observations," says Boyer, an instrument scientist on Webb's Near Infrared Camera (NIRCam) team at the Space Telescope Science Institute in Baltimore, Maryland.
The Early Universe via the Local Neighborhood
- Resolving and studying individual stars is necessary for understanding the bigger picture of how galaxies formed and function. Astronomers then can ask even bigger questions of how galaxies have evolved over time and space, from the distant, early universe to the Local Group—a collection of more than 20 nearby galaxies to which our galaxy belongs. Weisz explains that even though this observing program will be looking locally, there is evidence of the early universe to be discovered.
- "We will have Webb study a nearby, ultra-faint dwarf galaxy, a remnant of the first seed-galaxies to form in the universe, some of which eventually merged to form larger galaxies like the Milky Way," Weisz says. "At great distances these types of galaxies are too faint for even Webb to see directly, but small, local dwarf galaxies will show us what they were like billions of years ago."
- "We really need to understand the local universe in order to understand all of the universe," Boyer says. "The Local Group of galaxies is a sort of laboratory, where we can study galaxies in detail—every single component. In distant galaxies we can't resolve much detail, so we don't know exactly what's going on. A major step towards understanding distant or early galaxies is to study this collection of galaxies that is within our reach."
- As the Webb mission progresses, Boyer and Weisz expect that astronomers will use the tools their team develops in unexpected ways. They emphasize that developing the program was an effort of the entire local-universe astronomy community, and they plan to continue that collaboration once the data come in. Their observing-program team plans to host a workshop to go over the results of the program with other astronomers and tweak the software they've developed, all with the goal of assisting members of the astronomy community in applying for time to use Webb for their research.
- "I think that is really important—the idea of working together to achieve big science, as opposed to a lot of us trying to compete," Weisz says.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• December 16, 2020: Forming solar systems are a bit unkempt—a profusion of gas and dust, and an array of molecules orbits a star that's still gathering material. Over time, some of the dust bumps into one another, forming larger and larger particles until planets begin forming. Researchers know quite a bit about the outer regions of these planet-forming disks, but the inner areas, extending about as far as Saturn in our solar system, and the forming planets they may contain aren't yet well studied. NASA's James Webb Space Telescope's specialization in mid-infrared light, specifically its collection of data known as spectra, will help researchers model what's going on at the centers of these systems with unprecedented detail. 203)
- We live in a mature solar system—eight planets and several dwarf planets (like Pluto) have formed, the latter within the rock- and debris-filled region known as the Kuiper Belt. If we could turn back time, what would we see as our solar system formed? While we can't answer this question directly, researchers can study other systems that are actively forming—along with gas and dust that encircles their still-forming stars—to learn about this process.
- A team led by Dr. Thomas Henning of the Max Planck Institute for Astronomy in Heidelberg, Germany, will employ NASA's upcoming James Webb Space Telescope to survey more than 50 planet-forming disks in various stages of growth to determine which molecules are present and ideally pinpoint similarities, helping to shape what we know about how solar systems assemble.
- Their research with Webb will specifically focus on the inner disks of relatively nearby, forming systems. Although information about these regions has been obtained by previous telescopes, none match Webb's sensitivity, which means many more details will pour in for the first time. Plus, Webb's space-based location about a million miles (1.5 million kilometers) from Earth will give it an unobstructed view of its targets. "Webb will provide unique data that we can't get any other way," said Inga Kamp of the Kapteyn Astronomical Institute of the University of Groningen in the Netherlands. "Its observations will provide molecular inventories of the inner disks of these solar systems."
- This research program will primarily gather data in the form of spectra. Spectra are like rainbows—they spread out light into its component wavelengths to reveal high-resolution information about the temperatures, speeds, and compositions of the gas and dust. This incredibly rich information will allow the researchers to construct far more detailed models of what is present in the inner disks—and where. "If you apply a model to these spectra, you can find out where molecules are located and what their temperatures are," Henning explained.
- These observations will be incredibly valuable in helping the researchers pinpoint similarities and differences among these planet-forming disks, which are also known as protoplanetary disks. "What can we learn from spectroscopy that we can't learn from imaging? Everything!" Ewine van Dishoeck of Leiden University in the Netherlands exclaimed. "One spectrum is worth a thousand images."
Figure 149: Protoplanetary Disk Around the Dwarf Star PDS 70. PDS 70 is approximately 370 light-years away and features a large gap in its inner ring. The European Southern Observatory's Very Large Telescope provided the first clear image of a planet forming around the central star in 2018. The planet is a bright point to the right of the center of the image. The central star is black since its light was blocked by an instrument known as a coronagraph. A second planet has also been detected. This system is a future target of NASA's James Webb Space Telescope (image credit: ESO/A. Müller et al.)
A 'Mountain' of New Data
- Researchers have long studied protoplanetary disks in a variety of wavelengths of light, from radio to near-infrared. Some of the team's existing data are from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which collects radio light. ALMA excels at constructing images of the outer disks. If you were to compare the span of their outer disks to the size of our Solar System, this region is past Saturn's orbit. Webb's data will complete the picture by helping researchers model the inner disks.
- Some data already exist about these inner disks—NASA's retired Spitzer Space Telescope served as a pathfinder—but Webb's sensitivity and resolution are required to identify the precise quantities of each molecule as well as the elemental compositions of the gas with its data, known as spectra. "What used to be a very blurry peak in the spectrum will consist of hundreds if not thousands of detailed spectral lines," van Dishoeck said.
- Webb's specialty in mid-infrared light is particularly important. It will enable researchers to identify the "fingerprints" of molecules like water, carbon dioxide, methane, and ammonia—which can't be identified with any other existing instruments. The observatory will also determine how starlight impacts the chemistry and physical structures of the disks.
- Protoplanetary disks are complex systems. As they form, their mix of gas and dust is distributed into rings across the system. Their materials travel from the outer disk to the inner disk—but how? "The inner portion of the disk is a very dynamic place," explains Tom Ray of the Dublin Institute for Advanced Studies in Ireland. "It's not only where terrestrial-type planets form, but it's also where supersonic jets are launched by the star."
- Jets emitted by the star lead to a mixing of elements in the inner and outer disks, both by sending out particles and permitting other particles to move inward. "We think that as material leaves, it loses its spin, or angular momentum, and that this allows other material to move inward," Ray continued. "These exchanges of material will obviously impact the chemistry of the inner disk, which we're excited to explore with Webb."
Exciting Insights Await
- One of the research team's targets is TW Hydrae, which lies 196 light-years from Earth. This protoplanetary disk is close enough for Webb to image—which it will do while blocking the star to more clearly identify forming planets. It will also return a slew of spectra to detail the molecules in its inner disk. Existing data show a prominent inner area cleared of debris, which is where planets may be forming. Henning's team hopes to identify and characterize them with Webb.
- PDS 70 is farther at 370 light-years away. It also has a large gap in its inner ring, plus data have revealed that two forming planets, known as protoplanets, are present and gathering material. "Webb's mid-infrared measurements will help us refine what we know about them, as well as the material around them," Kamp explained.
- With dozens of targets on their list, it's difficult for team members to play favorites. "I love them all," Henning said. "One question I'd like to answer concerns the connection between the composition of planet-forming disks and the planets themselves. With Webb, we will observe far more detail about which types of material are available for a potential planet to accrete."
- After refining the data, his team will apply the discrete data points to models. "This will allow us to do a graphic reconstruction of these systems," he continued. These models will be shared with the astronomical community, enabling other scientists to examine the data, and make their own projections or glean new findings. These studies will be conducted through a Guaranteed Time Observations (GTO) program.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• November 18, 2020: Dust may seem insignificant, but it plays a huge role in the universe, from the formation of stars and planets to facilitating the complex chemistry that becomes the stuff of life—including us. Big questions like "How did we get here?" come down to dust, and yet the origin and formation process of cosmic dust has eluded scientists. Astronomers refer to the unexplained abundance of dust in galaxies as the "dust budget crisis." It is a mystery that astronomers are excited to get to work solving using the specialized technology of NASA's James Webb Space Telescope. 204)
- Discovering too much money in your bank account may not be what you would call a "crisis," but it would still be unexpected and you should figure out how it got there. Astronomers find themselves in a similar position when calculating the amount of dust galaxies should have; there is more dust than expected, and they don't know where it's coming from. This matters because cosmic dust is essential to the function of the universe: it shelters forming stars, becomes part of planets, and can contain the organic compounds that lead to life as we know it. Dust led to us.
- "What we refer to as the 'dust budget crisis' is the major problem in astronomy of not being able to account for all the dust that's observed in galaxies, both in the nearby and distant, early universe," says Ryan Lau of the Japan Aerospace Exploration Agency. Lau is leading an Director's Discretionary-Early Release Science Program with NASA's upcoming James Webb Space Telescope to study dust-producing Wolf-Rayet binary stars.
- Wolf-Rayet stars are very hot and very bright. There is evidence that Wolf-Rayet stars, through interactions with a companion star, produce large amounts of dust in a distinctive pinwheel pattern as the two stars orbit each other and their stellar winds collide. It is possible that these binary-star systems account for a large percentage of a galaxy's "dust budget." However, the intense luminosity and heat coming from the Wolf-Rayet stars has made it difficult to study the faint, more diffuse dust of these systems. This is where Webb comes in.
- "Webb has an unprecedented combination of spatial resolution and sensitivity in mid-infrared wavelengths that is really what enables us to conduct these interesting observations," Lau says. "We can achieve the spatial resolution from ground-based telescopes, but lack the sensitivity that Webb can achieve from its observing location in space, without the interference of Earth's atmosphere. Conversely, with previous infrared space-based telescopes like NASA's Spitzer mission, we could achieve the sensitivity but lacked the spatial resolution."
Figure 150: Evidence indicates that large amounts of cosmic dust are produced as the stellar winds of massive stars collide in Wolf-Rayet binary or multiple-star systems. As the stars orbit each other and dust is produced, a distinctive pinwheel pattern is formed, as shown in this image from the European Southern Observatory. Warm dust like this glows in the mid-infrared wavelengths of light detectable by NASA's James Webb Space Telescope. Confirming the origin of dust will help account for the mysterious over-abundance of it found in galaxies, which is crucial to the later development of stars, planets, and life as we know it (image credit: ESO)
Targeting Two Dust Factories
- Lau and the Director's Discretionary-Early Release Science (DD-ERS) team will use Webb to study two Wolf-Rayet binary systems, using the telescope's Mid-Infrared Instrument (MIRI) and Near Infrared Imager and Slitless Spectrograph (NIRISS). The WR140 binary system has been studied extensively in many wavelengths of light and so will provide a good baseline for gauging Webb's best observing modes for this kind of cosmic subject. Another Wolf-Rayet binary, WR137, will experience its stars' closest approach to each other—when the most dust is thought to be produced—early in Webb's mission when the DD-ERS program observations are scheduled.
- Beyond new discoveries about the formation and chemical composition of dust, the DD-ERS program also will be among the first opportunities astronomers have to test out best practices for Webb's instruments and processing the data it delivers.
- "This DD-ERS program will look at the best ways to maximize Webb's dynamic range—the difference between the brightest and faintest objects it observes—and that will be useful to the astronomy community in many ways in the future; for example, in studying the dusty disk surrounding the bright center of an active galaxy, or finding a planet orbiting a bright star," says Mansi Kasliwal, another astronomer on the DD-ERS team. Kasliwal led the laboratory at the California Institute of Technology where Lau performed his post-doctoral research on Wolf-Rayet binaries and developed the proposal for the DD-ERS program.
- Both Lau and Kasliwal agree that while the open question of how cosmic dust is created and disseminated throughout the universe is a fascinating one, it is really a stepping stone toward answering one of the biggest questions ever posed: How did we get here? As far as we know, Earth is an island of life in the universe, and in seeking to understand something as seemingly remote as cosmic dust, Lau says that we are ultimately seeking to understand ourselves. "Understanding the formation of dust is critical for us to trace our own cosmic origins," Lau says. "Webb is one of the most powerful scientific tools ever built in the quest to find answers to these fundamental questions."
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• October 28, 2020: Beyond the orbit of Neptune, a diverse collection of thousands of dwarf planets and other relatively small objects dwells in a region called the Kuiper Belt. These often-pristine leftovers from our solar system's days of planet formation are called Kuiper Belt Objects, or Trans-Newtonian Objects. NASA's upcoming James Webb Space Telescope will examine an assortment of these icy bodies in a series of programs called Guaranteed Time Observations shortly after its launch in 2021. The goal is to learn more about how our solar system formed. 205)
- "These are objects that are in the graveyard of solar system formation," explained Cornell University's Jonathan Lunine, a Webb Interdisciplinary Scientist who will use Webb to study some of these targets. "They're in a place where they could last for billions of years, and there aren't many places like that in our solar system. We'd love to know what they're like."
- By studying these bodies, Lunine and his colleagues hope to learn about which ices were present in the early solar system. These are the coldest worlds to display geologic and atmospheric activity, so scientists are also interested in comparing them with the planets.
- Kuiper Belt Objects are very cold and faint, yet they glow in infrared light, which is at wavelengths beyond what our human eyes can see. Webb is specifically designed to detect infrared light. To study these distant objects, scientists mainly will use a technique called spectroscopy, which divides light into its individual colors to determine the properties of materials that interact with that light.
Figure 151: Pluto and its largest moon, Charon, are two of the best-known residents of the Kuiper Belt. This composite of enhanced color images of Pluto (lower right) and Charon (upper left), was taken by NASA's New Horizons spacecraft as it passed through the Pluto system on July 14, 2015. The color and brightness of both Pluto and Charon have been processed identically to allow direct comparison of their surfaces, and to highlight the similarity between Charon's polar red terrain and Pluto's equatorial red terrain. Pluto and Charon are shown with approximately correct relative sizes, but their true separation is not to scale (image credits: NASA/JHUAPL/SwRI)
- "These are objects that are in the graveyard of solar system formation," explained Cornell University's Jonathan Lunine, a Webb Interdisciplinary Scientist who will use Webb to study some of these targets. "They're in a place where they could last for billions of years, and there aren't many places like that in our solar system. We'd love to know what they're like."
- By studying these bodies, Lunine and his colleagues hope to learn about which ices were present in the early solar system. These are the coldest worlds to display geologic and atmospheric activity, so scientists are also interested in comparing them with the planets.
- Kuiper Belt Objects are very cold and faint, yet they glow in infrared light, which is at wavelengths beyond what our human eyes can see. Webb is specifically designed to detect infrared light. To study these distant objects, scientists mainly will use a technique called spectroscopy, which divides light into its individual colors to determine the properties of materials that interact with that light.
A Wide Assortment
- The denizens of the Kuiper Belt come in various shapes and sizes. Some reside in pairs or multiples, while others have rings or moons. They exhibit a wide range of colors, which may indicate different formation histories or different exposure to sunlight.
- "Some seem to be redder in color, others are bluer. Why is that?" said Heidi Hammel, a Webb Interdisciplinary Scientist for solar system observations. She is also Vice President for Science at the Association of Universities for Research in Astronomy (AURA) in Washington, D.C. "Using Webb, we will be able to get information about surface chemistry that might be able to give us some clues into why there are these different populations in the Kuiper Belt."
Figure 152: This global color mosaic of Neptune's moon Triton, likely a captured KBO, was taken in 1989 by Voyager 2 during its flyby of the Neptune system. Triton is by far the largest satellite of Neptune (image credits: NASA/JPL/USGS)
Kicked out of the Club
- Between Jupiter and Neptune, and crossing the orbit of one or more of the giant planets, lies a different population of objects called centaurs. These are small solar system bodies that have been ejected from the Kuiper Belt. In addition to observing current Kuiper Belt Objects, these Webb programs will study such solar system bodies that have been "kicked out of the club." These former Kuiper Belt Objects have orbits that have been dramatically disturbed, bringing them significantly closer to the Sun.
- "Because they cross the orbits of Neptune, Uranus, and Saturn, centaurs are short-lived. So they are typically only around for about 10 million years," explained John Stansberry of the Space Telescope Science Institute in Baltimore, Maryland. Stansberry is leading a different team that will use Webb to study Kuiper Belt Objects. "By that point, they have an interaction with one of the major planets that's very strong, and they either get thrown into the Sun or thrown out of the solar system."
- Another body that Webb will study is Neptune's moon Triton. The largest of the ice giant's 13 moons, Triton shares many similarities with Pluto. "Even though it's Neptune's moon, we have evidence to suggest that it is a Kuiper Belt Object that got too close to Neptune sometime in its past, and it was captured into orbit around Neptune," said Hammel. "Triton was studied by the Voyager 2 probe in 1989. That spacecraft data will provide us very important 'ground truth' for our Webb observations of Kuiper Belt Objects."
A Sampling of the Targets
- Here is a small sampling of some of the dozens of current and former Kuiper Belt Objects that Webb will observe:
a) Pluto and Charon: The dwarf planet Pluto and its largest moon, Charon, are two of the most well-known residents of the Kuiper Belt. Pluto boasts an atmosphere, haze, and seasons. It has geologic activity on its surface and may have an ocean in its interior. In addition to Charon, it hosts four other moons: Nix, Hydra, Styx, and Kerberos. The Webb data will complement the observations made by NASA's New Horizons spacecraft when it flew by the Pluto system in 2015.
b) Eris: Nearly the size of Pluto, Eris is the second-largest known dwarf planet in the solar system. At its farthest point, mysterious Eris is more than 97 times as far from the Sun as the Earth is. Because of its distance, it is difficult to observe, but Webb will tell scientists quite a bit about what kinds of ices are on its surface.
c)- Sedna: With its deep red hue, Sedna is actually located beyond the main Kuiper Belt. It takes approximately 11,400 years to complete one orbit, and the farthest point of that highly elongated orbit is estimated to be 940 times Earth's distance from the Sun.
d) Haumea: This large, rapidly spinning body is egg-shaped, and scientists would like to know why. In addition to moons, it also seems to have a ring system. With Webb, scientists hope to learn more about how those rings formed.
e) Chariklo: The largest centaur, Chariklo is also the first asteroid found to have a ring system. It was the fifth ring system found in our solar system—after Saturn, Jupiter, Uranus and Neptune. The rings are believed to be between two and four miles wide.
- Another program, called a Target of Opportunity, will observe a Kuiper Belt Object passing in front of a star, if such an alignment should occur during the first two years of Webb's lifetime. Called an occultation, this type of observation can reveal an object's size.
- The few spacecraft that have flown by Kuiper Belt Objects could only study these intriguing objects for a very short period of time. With Webb, astronomers can target more Kuiper Belt Objects over an extended time. The result will be new insights into our solar system's earliest history.
- The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
• July 31 2020: NASA's James Webb Space Telescope will have a challenging early assignment in the solar system: observe the largest, fastest-rotating planet—Jupiter—as well as its faint rings and two of the four Galilean satellites: icy Ganymede and fiery Io. In addition to laying groundwork for the rest of Webb's mission, the ambitious program should yield new scientific insights, not only into the Jovian system, but also the geological history of Earth and exoplanet science. 206)
Jupiter, named for the king of the ancient Roman gods, commands its own mini-version of our solar system of circling satellites; their movements convinced Galileo Galilei that Earth is not the center of the universe in the early 17th century. More than 400 years later, astronomers will use NASA's James Webb Space Telescope to observe these famous subjects, pushing the observatory's instruments to their fullest capabilities and laying the groundwork for far-reaching scientific discovery.
A diverse team of more than 40 researchers, led by astronomers Imke de Pater of the University of California, Berkeley and Thierry Fouchet of the Observatoire de Paris, have designed an ambitious observing program that will conduct some of Webb's first scientific observations in the solar system—studying Jupiter, its ring system, and two of its moons: Ganymede and Io.
"It will be a really challenging experiment," said de Pater. "Jupiter is so bright, and Webb's instruments are so sensitive, that observing both the bright planet and its fainter rings and moons will be an excellent test of how to get the most out of Webb's innovative technology."
Figure 153: Jupiter and Io. The moon Io orbits Jupiter in this image from NASA's Cassini spacecraft. Io is similar in size to Earth's moon. Jupiter and Io appear deceptively close in this image, when in fact the moon is orbiting 217,000 miles from the gas giant planet (image credit: NASA/JPL/University of Arizona)
Jupiter: In addition to calibrating Webb's instruments for Jupiter's brightness, astronomers must also take into account the planet's rotation, because Jupiter completes one day in only 10 hours. Several images must be stitched together in a mosaic to fully capture a certain area—the famous storm known as the Great Red Spot, for example—a task made more difficult when the object itself is moving. While many telescopes have studied Jupiter and its storms, Webb's large mirror and powerful instruments will provide new insights.
We know that the immediate atmosphere above the Great Red Spot is colder than other areas of Jupiter, but at higher altitudes, in the mesosphere, the atmosphere appears to be warmer. We will use Webb to investigate this phenomenon," de Pater said.
Webb will also examine the atmosphere of the polar region, where NASA's Juno spacecraft discovered clusters of cyclones. Webb's spectroscopic data will provide much more detail than has been possible in past observations, measuring winds, cloud particles, gas composition, and temperature.
Future solar system observations of the giant planets with Webb will benefit from the lessons learned in these early observations of the Jovian system. The team is tasked with developing methods for working with Webb observations of solar system planets, which can be used later by other scientists.
Rings: All four of the gas giant planets of the solar system have rings, with Saturn's being the most prominent. Jupiter's ring system is composed of three parts: a flat main ring; a halo inside the main ring, shaped like a double-convex lens; and the gossamer ring, exterior to the main ring. Jupiter's ring system is exceptionally faint because the particles that make up the rings are so small and sparse that they do not reflect much light. Next to the brightness of the planet they practically disappear, presenting a challenge for astronomers.
"We are really pushing the capabilities of some of Webb's instruments to the limit to get a unique new set of observations," said co-investigator Michael Wong of the University of California, Berkeley. The team will test observing strategies to deal with Jupiter's scattered light, and build models for use by other astronomers, including those studying exoplanets orbiting bright stars.
The team will look to make new discoveries in the rings as well. De Pater noted that there may be undiscovered "ephemeral moonlets" in the dynamic ring system, and potential ripples in the ring from comet impacts, like those observed and traced back to the impact of Comet Shoemaker-Levy 9 in 1994.
Ganymede: Several features of icy Ganymede make it fascinating for astronomers. Aside from being the largest moon in the solar system, and larger even than the planet Mercury, it is the only moon known to have its own magnetic field. The team will investigate the very outer parts of Ganymede's atmosphere, its exosphere, to better understand the moon's interaction with particles in Jupiter's magnetic field.
There is also evidence that Ganymede may have a liquid saltwater ocean beneath its thick surface ice, which Webb will investigate with detailed spectroscopic study of surface salts and other compounds. The team's experience studying Ganymede's surface may be useful in the future study of other icy solar system moons suspected of having subsurface oceans, including Saturn's moon Enceladus and fellow Jovian satellite Europa.
Io: In dramatic contrast to Ganymede is the other moon the team will study, Io, the most volcanically active world in the solar system. The dynamic surface is covered with hundreds of huge volcanoes that would dwarf those on Earth, as well as lakes of molten lava and smooth floodplains of solidified lava. Astronomers plan to use Webb to learn more about the effects of Io's volcanoes on its atmosphere.
"There is still much we don't know about Io's atmospheric temperature structure, because we haven't had the data to distinguish the temperature at different altitudes," said de Pater. "On Earth we take for granted that as you hike up a mountain, the air gets cooler—would it be the same on Io? Right now we don't know, but Webb may help us to find out."
Another mystery Webb will investigate on Io is the existence of "stealth volcanoes," which emit plumes of gas without the light-reflecting dust that can be detected by spacecraft like NASA's Voyager and Galileo missions, and so have thus far gone undetected. Webb's high spatial resolution will be able to isolate individual volcanoes that previously would have appeared as one large hotspot, allowing astronomers to gather detailed data on Io's geology.
Webb will also provide unprecedented data on the temperature of Io's hotspots, and determine if they are closer to volcanism on Earth today, or if they have a much higher temperature, similar to the environment on Earth in the early years after its formation. Previous observations by the Galileo mission and ground observatories have hinted at these high temperatures; Webb will follow up on that research and provide new evidence that may settle the question.
Team Effort: Webb's detailed observations will not supplant those of other observatories, but rather coordinate with them, Wong explained. "Webb's spectroscopic observations will cover just a small area of the planet, so global views from ground-based observatories can show how the detailed Webb data fit in with what's happening on a larger scale, similar to how Hubble and the Gemini Observatory provide context for Juno's narrow, close-up observations."
In turn, Webb's study of Jupiter's storms and atmosphere will complement Juno data, including radio signals from lightning, which Webb does not detect. "No one observatory or spacecraft can do it all," Wong said, "so we are very excited about combining data from multiple observatories to tell us much more than we could learn from only a single source."
This research is being conducted as part of a Webb Early Release Science (ERS) program. This program provides time to selected projects early in the observatory's mission, allowing researchers to quickly learn how best to use Webb's capabilities, while also yielding robust science.
The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Mapping the Early Universe with NASA's Webb Telescope
• June 24, 2020: Astronomers and engineers have designed telescopes, in part, to be "time travelers." The farther away an object is, the longer its light takes to reach Earth. Peering back in time is one reason why NASA's upcoming James Webb Space Telescope specializes in collecting infrared light: These longer wavelengths, which were initially emitted by stars and galaxies as ultraviolet light more than 13 billion years ago, have stretched, or redshifted, into infrared light as they traveled toward us through the expanding universe. 207) 208)
Although many other observatories, including NASA's Hubble Space Telescope, have previously created "deep fields" by staring at small areas of the sky for significant chunks of time, the Cosmic Evolution Early Release Science (CEERS) Survey, led by Steven L. Finkelstein of the University of Texas at Austin, will be one of the first for Webb. He and his research team will spend just over 60 hours pointing the telescope at a slice of the sky known as the Extended Groth Strip, which was observed as part of Hubble's Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey or CANDELS.
"With Webb, we want to do the first reconnaissance for galaxies even closer to the big bang," Finkelstein said. "It is absolutely not possible to do this research with any other telescope. Webb is able to do remarkable things at wavelengths that have been difficult to observe in the past, on the ground or in space."
Mark Dickinson of the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory in Arizona, and one of the CEERS Survey co-investigators, gives a nod to Hubble while also looking forward to Webb's observations. "Surveys like the Hubble Deep Field have allowed us to map the history of cosmic star formation in galaxies within a half a billion years of the big bang all the way to the present in surprising detail," he said. "With CEERS, Webb will look even farther to add new data to those surveys."
Figure 154: The CEERS Survey researchers will use the James Webb Space Telescope to observe the Extended Groth Strip in infrared light. Their observations employ three of the telescope's instruments and will provide both images and spectra of the objects in the field — which includes at least 50,000 galaxies — helping to expand what we know about galaxies in the very early universe [image credits: NASA, ESA, and M. Davis (University of California, Berkeley)]
Delivering the Unseen
What was the early universe like? There are certainly many data points, but not enough to create an exhaustive census of its conditions. Plus, researchers' knowledge and assumptions are updated frequently — each time a new deep exposure is released. "Every time we look farther, we find galaxies earlier and earlier than we thought possible," said CEERS Survey co-investigator Jeyhan Kartaltepe of the Rochester Institute of Technology in New York. "The conditions in the very early universe had to be right for galaxies to form — and they formed and became massive very quickly."
"The universe was more compact at this time, which means stars and galaxies could have formed at a greater efficiency," Finkelstein added. "Some models predict we'll find 50 galaxies at earlier eras more distant than Hubble can reach, but others predict we will only find a few. In both cases, the data will help us constrain galaxy formation in the early universe."
The CEERS Survey team hopes to identify an abundance of distant objects, including the most distant galaxies in the universe, early galaxy mergers and interactions, the first massive or supermassive black holes, and even earlier quasars than previously identified. These potential "firsts" are only the beginning of the value of this research: The team, which is made up of over 100 researchers from around the world, will go on to classify many objects in the field. "These data will help demonstrate what the structure of the universe was like at various periods," Finkelstein explained.
Hitting "Rewind"
Perhaps the most exciting element of this research is how the team will use the data to uncover new findings about an important period of the universe's history called the "Era of Reionization." The big bang set off a series of events, leading to the cosmic microwave background, the dark ages, the first stars and galaxies — and then to the Era of Reionization. During this period, the gas in the universe transformed from mostly neutral, meaning it was opaque to ultraviolet light, and became completely ionized, which allowed it to be transparent. Ionization means the atoms were stripped of their electrons — eventually leading to the "clear" conditions detected in much of the universe today.
Many questions remain about this unique time in our universe. For example, what was responsible for converting the gas from neutral to ionized? And how long did it take before the universe became significantly less opaque and much more transparent?
Figure 155: Our view of the universe wasn't always so clear. More than 13 billion years ago, neutral gas made the universe opaque to some types of light. Over hundreds of millions of years, the universe became transparent as its gas particles became charged or ionized. What caused the gas to change? The James Webb Space Telescope will peer deep into space to gather more information about objects in this period, known as the Era of Reionization, to help us understand this major transition in the history of the universe (Ref. 208).
"We think this happened when ultraviolet light escaped young, forming galaxies," Dickinson explained. "There may be other factors. For example, early accreting black holes may also have emitted ultraviolet light that eventually helped transform the gas."
Where the galaxies appear on the sky offers another clue. "We'll examine reionization-era galaxies to see if they are clustered together in the same regions or if they are more isolated," said Kartaltepe. "We have a lot of ideas about what causes galaxies to grow and become more massive, but we need more comprehensive information about these galaxies to fully understand how they initially grew and evolved."
The presence of galactic mergers or interactions — or lack thereof — will also help the team trace the conditions of the environment during the Era of Reionization. "The CEERS Survey will give us hints about how this period proceeded," Dickinson adds. "We will certainly learn about the galaxies we think are responsible, and also hope to learn about the ionizing radiation that escaped them."
The team has designed the CEERS Survey to provide as much complementary data as possible for many targets in this field of view. They will employ three of Webb's instruments, in several modes, to obtain images of the Extended Groth Strip, in addition to spectra. Spectra are invaluable data since they help researchers identify the colors, temperatures, motions, and masses of each target, and provide a much more in-depth look at the chemical makeup of distant objects.
"That's the difference with Webb's NIRSpec (Near-Infrared Spectrograph)," Dickinson emphasized. "We'll open the spectrograph's microshutter slits to individually observe hundreds of galaxies to obtain their spectra for the first time."
Beginning to Build a Census
In the months following the initial data release, the CEERS Survey researchers will create and post new tools and catalogs any researcher can use to analyze the data, including masses of galaxies, galaxy shapes, and photometric redshifts. "With the same set of observations, hundreds of researchers can conduct hundreds of science experiments," Kartaltepe said. "We're also going to find things we didn't even think to ask, which is one more reason why the CEERS Survey research will be so rewarding."
"Our hope is that the CEERS Survey will influence future distant galaxy surveys with Webb," Finkelstein added. "It will also demonstrate to the community that observing with a variety of instruments and modes are very valid ways to increase Webb's scientific yield."
This research is being conducted as part of a Webb Early Release Science (ERS) program. This program provides time to selected projects early in the telescope's mission, allowing researchers to quickly learn how best to use Webb's capabilities, while also yielding robust science.
The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
NASA's Webb Telescope Will Study an Iconic Supernova
• February 28, 2019: Within a galaxy known as the Large Magellanic Cloud, a star exploded 160,000 years ago. In 1987, light from that exploding star reached Earth. Over the past 32 years, astronomers have studied Supernova 1987A to learn about the physics of supernovas and their gaseous remnants. Those observations have revealed a surprising amount of dust, up to an entire sun's worth. NASA's infrared James Webb Space Telescope will study the dust within SN 1987A to learn about its composition, temperature and density. 209)
In February 1987, light from an exploding star arrived at Earth after traveling across 160,000 light-years of space. It was the closest supernova humanity had seen in centuries. Thirty-two years later, the light of the supernova itself has faded, but astronomers continue to study its remains for clues about how stars live and die. Scientists will use NASA's James Webb Space Telescope to observe Supernova 1987A (SN 1987A), as it is known, in order to gain new insights into the physics of the explosion and its aftermath.
When you look at a photo of SN 1987A, two features stand out: a clumpy outer ring that looks like a pearl necklace, and an inner blob. The outer ring is material that the star shed thousands of years ago. When the supernova's blast wave hit this ring, it caused the previously invisible material to heat up and glow. The inner blob is material ejected when the star exploded.
That ejected material revealed a surprise when astronomers observed it with the European Space Agency's infrared Herschel Space Observatory. They found that it contained an entire sun's worth of cold dust. More recently, NASA's SOFIA (Stratospheric Observatory for Infrared Astronomy) mission studied the ring and detected 10 times more dust than expected, indicating a growing amount of dust there, too.
Theories suggest that any dust within the ring that predated the explosion should have been destroyed by the blast wave, and the ejecta itself should be too hot for new dust to form. As a result, there should be little dust within SN 1987A. Yet observations tell a different story.
"Something has produced dust there. We need Webb to answer questions like, how was the dust produced, and what is it made of?" said lead researcher Margaret Meixner of the Space Telescope Science Institute and Johns Hopkins University, both in Baltimore, Maryland.
Figure 156: Multiwavelength view of Supernova 1987A. Astronomers combined observations from three different observatories ALMA (Atacama Large Millimeter/submillimeter Array), red; Hubble, green; Chandra X-ray Observatory, blue) to produce this colorful, multiwavelength image of the intricate remains of Supernova 1987A [image credit: NASA, ESA, A. Angelich (NRAO/AUI/NSF); Hubble credit: NASA, ESA, R. Kirshner; Chandra credit: NASA/CXC/Penn State/K. Frank et al.; ALMA credit: ALMA (ESO/NAOJ/NRAO) and R. Indebetouw (NRAO/AUI/NSF)]
What is dust, and why is it important?
Cosmic dust is different from the dust bunnies that you find under your furniture. It's smaller, mainly consisting of µm-sized particles like those in smoke. And rather than being made of bits of hair or clothing fibers, cosmic dust is composed of a variety of chemical elements like carbon, silicon and iron all stuck together. As a result, measuring the composition of a particular patch of cosmic dust is challenging because the signatures of the elements blend together.
"We have no clue what the dust in Supernova 1987A is made of – whether it's rocky and silicate-rich, or sooty and carbon-rich. Webb will let us learn not only the composition of the dust, but its temperature and density," explained Olivia Jones of the United Kingdom Astronomy Technology Center, a co-investigator on the project.
As dust from dying stars spreads through space, it carries essential elements to help seed the next generation of star and planet formation. "Dust is what the planets are made out of, what we're made out of. Without dust, you have no planets," said Jones.
Dust also is important for the evolution of galaxies. Observations have shown that distant, young galaxies had lots of dust. Those galaxies weren't old enough for sun-like stars to create so much dust, since sun-like stars last for billions of years. Only more massive, short-lived stars could have died soon enough and in large enough numbers to create the vast quantities of dust astronomers see in the early universe.
The birth of a supernova remnant
The team plans to examine SN 1987A with two of Webb's instruments: the Mid-Infrared Imager (MIRI) and the Near-Infrared Spectrograph (NIRSpec). With imaging, Webb will reveal features of SN 1987A far beyond any previous infrared observations due to its exquisite resolution. Astronomers expect to be able to map the temperature of the dust within both the supernova ejecta and the surrounding ring. They can also study the interaction of the blast wave with the ring in great detail.
Webb's true power will come from its spectroscopic measurements. By spreading light out into a rainbow spectrum of colors, scientists can determine not only chemical compositions but also temperatures, densities, and speeds. They can examine the physics of the blast wave, and determine how it is affecting the surrounding environment. They can also watch the evolution of the ejected material and ring over time.
"We're witnessing the birth of a supernova remnant," said Patrice Bouchet of DRF/Irfu/Astrophysics Department, CEA-Saclay in France, a co-principal investigator for the MIRI European Consortium. "This is a once-in-a-lifetime event."
"Supernova 1987A is an object that continually surprises people," said Meixner. "This is one you'll want to keep your eyes open for!"
The observations described here will be taken as part of Webb's Guaranteed Time Observation (GTO) program. The GTO program provides dedicated time to the scientists who have worked with NASA to craft the science and instrument capabilities of Webb throughout its development.
The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency.
How to Weigh a Black Hole Using JWST
October 17, 2018: At first glance, the galaxy NGC 4151 looks like an average spiral. Examine its center more closely, though, and you can spot a bright smudge that stands out from the softer glow around it. That point of light marks the location of a supermassive black hole weighing about 40 million times as much as our Sun. 210)
Astronomers will use NASA's James Webb Space Telescope to measure that black hole's mass. The result might seem like a piece of trivia, but its mass determines how a black hole feeds and affects the surrounding galaxy. And since most galaxies contain a supermassive black hole, learning about this nearby galaxy will improve our understanding of many galaxies across the cosmos.
"Some central questions in astrophysics are: How does a galaxy's central black hole grow with time; how does the galaxy itself grow with time; and how do they affect each other? This project is a step toward answering those questions," explained Misty Bentz of Georgia State University, Atlanta, the principal investigator of the project.
Figure 157: The spiral galaxy NGC 4151 has a bright, active core powered by a supermassive black hole. Webb will weigh the black hole by measuring the motions of stars at the galaxy's center [image credits: NASA, ESA, and J. DePasquale (STScI)]
Probing a galaxy's core: There are several methods of weighing supermassive black holes. One technique relies on measuring the motions of stars in the galaxy's core. The heavier the black hole, the faster nearby stars will move under its gravitational influence.
NGC 4151 represents a challenging target, because it contains a particularly active black hole that is feeding voraciously. As a result, the material swirling around the black hole, known as an accretion disk, shines brightly. The light from the accretion disk threatens to overwhelm the fainter light from stars in the region.
"With Webb's beautifully shaped mirrors and sharp 'vision,' we should be able to probe closer to the galaxy's center even though there's a really bright accretion disk there," said Bentz.
The team expects to be able to investigate the central 1,000 light-years of NGC 4151, and be able to resolve stellar motions on a scale of about 15 light-years.
A thousand spectra at once: To achieve this feat, the team will use Webb's NIRSpec (Near-Infrared Spectrograph) integral field unit, or IFU. It will be the first IFU flown in space, and it has a unique capability.
Webb's IFU takes the light from every location in an image and splits it into a rainbow spectrum. To do this it employs almost 100 mirrors, each of them precision crafted to a specific shape, all squeezed into an instrument the size of a shoebox. Those mirrors effectively slice a small square of the sky into strips, then spread the light from those strips out both spatially and in wavelength.
In this way a single image yields 1,000 spectra. Each spectrum tells astronomers not only about the elements that make up the stars and gas at that exact point of the sky, but also about their relative motions.
Despite Webb's exquisite resolution, the team won't be able to measure the motions of individual stars. Instead, they will get information about groups of stars very close to the center of the galaxy. They will then apply computer models to determine the gravitational field affecting the stars, which depends on the size of the black hole.
"Our computer code generates a bunch of mock stars – tens of thousands of stars, mimicking the motions of real stars in the galaxy. We put in a variety of different black holes and see what matches the observations the best," said Monica Valluri of the University of Michigan, a co-investigator on the project.
The result of this technique will be compared with a second one that focuses on the gas at the galaxy's center, rather than the stars.
"We should get the same answer, no matter what technique we use, if we're looking at the same black hole," said Bentz. "NGC 4151 is one of the best targets for making that comparison."
These observations will be taken as part of the Director's Discretionary-Early Release Science program. The DD-ERS program provides time to selected projects enabling the astronomical community to quickly learn how best to use Webb's capabilities, while also yielding robust science.
The James Webb Space Telescope will be the world's premier space science observatory. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).
Concept Launch Observatory Sensor Complement Spacecraft Bus and Sunshield
Development Status Spinoff Technologies Feature Stories Supernova Study
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2d 3d Motion Designer Space Telescope Institute
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