JWST (James Webb Space Telescope)

JWST (James Webb Space Telescope)

Concept    Launch    Mission Status   Observatory   Sensor Complement    Spacecraft Bus and Sunshield Spinoff Technologies    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. 69).

 

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)

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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)

 

 

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Figure 2: Comparison of JWST light gathering power vs spectral range with Hubble and Spitzer telescopes (image credit: STScI) 13)

 

Launch: On Saturday, December 25 (Christmas), 2021 at 9:20 am local time (12:20 UTC), an Ariane 5 rocket lifted off from the Guiana Space Center, Europe's Spaceport in Kourou, French Guiana (South America), injecting the Webb Space Telescope, developed by NASA in partnership with ESA and the Canadian Space Agency (CSA), into its transfer orbit. The telescope was successfully separated from the launcher 27 minutes after liftoff. 14) 15)

The telescope now embarks on a voyage lasting 29 days to reach the second Lagrange point.

• On the third day, the heat shield will begin to deploy. On the eleventh day, the secondary mirror will begin positioning.

• Between the 13th and 14th day, the primary mirror, comprising 18 hexagonal segments and measuring 6.5 meters in diameter, will be assembled.

• The telescope is slated to arrive at its final destination, 1.5 million kilometers from Earth, approximately 29 days after launch.

The space agencies of the United States (NASA), Europe (ESA) and Canada (CSA) teamed up to develop this telescope. Europe played an important role in this mission, with ESA providing the launch onboard Ariane 5, as well as the Nirspec spectrometer built by Airbus. The astrophysics department of the Saclay-based CEA (French Alternative Energies and Atomic Energy Commission) and the Paris Observatory designed the MIRI camera. This is the most ambitious telescope ever sent into space.

"Today's launch is the mission of the decade," said Stephane Israël, Chief Executive Officer of Arianespace, "one that demonstrates the reliability of Arianespace's launch services in the eyes of the international space community. It's a great honor for us to have been chosen for this launch, which will enable humanity to take a giant step forward in its knowledge of the Universe. The mission demanded 20 years of preparation hand in hand with NASA. It's the third launch we have performed for the American space agency, clearly illustrating the advantage of large-scale international collaboration in space. I would like to thank ESA, NASA and CSA for entrusting us with their invaluable payload. To launch on Christmas morning 42 years after the takeoff of the first Ariane from this same Kourou site ... What a great end of year present for the space community gathered today for this launch.

NASA: A joint effort with ESA (European Space Agency) and the Canadian Space Agency, the Webb observatory is NASA's revolutionary flagship mission to seek the light from the first galaxies in the early universe and to explore our own solar system, as well as planets orbiting other stars, called exoplanets. 16)

"The James Webb Space Telescope represents the ambition that NASA and our partners maintain to propel us forward into the future," said NASA Administrator Bill Nelson. "The promise of Webb is not what we know we will discover; it's what we don't yet understand or can't yet fathom about our universe. I can't wait to see what it uncovers!"

Ground teams began receiving telemetry data from Webb about five minutes after launch. The Arianespace Ariane 5 rocket performed as expected, separating from the observatory 27 minutes into the flight. The observatory was released at an altitude of approximately 870 miles (1,400 km). Approximately 30 minutes after launch, Webb unfolded its solar array, and mission managers confirmed that the solar array was providing power to the observatory. After solar array deployment, mission operators will establish a communications link with the observatory via the Malindi ground station in Kenya, and ground control at the Space Telescope Science Institute in Baltimore will send the first commands to the spacecraft.

Engineers and ground controllers will conduct the first of three mid-course correction burns about 12 hours and 30 minutes after launch, firing Webb's thrusters to maneuver the spacecraft on an optimal trajectory toward its destination in orbit about 1 million miles from Earth.

"I want to congratulate the team on this incredible achievement – Webb's launch marks a significant moment not only for NASA, but for thousands of people worldwide who dedicated their time and talent to this mission over the years," said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "Webb's scientific promise is now closer than it ever has been. We are poised on the edge of a truly exciting time of discovery, of things we've never before seen or imagined."

The world's largest and most complex space science observatory will now begin six months of commissioning in space. At the end of commissioning, Webb will deliver its first images. Webb carries four state-of-the-art science instruments with highly sensitive infrared detectors of unprecedented resolution. Webb will study infrared light from celestial objects with much greater clarity than ever before. The premier mission is the scientific successor to NASA's iconic Hubble and Spitzer space telescopes, built to complement and further the scientific discoveries of these and other missions.

"The launch of the Webb Space Telescope is a pivotal moment – this is just the beginning for the Webb mission," said Gregory L. Robinson, Webb's program director at NASA Headquarters. "Now we will watch Webb's highly anticipated and critical 29 days on the edge. When the spacecraft unfurls in space, Webb will undergo the most difficult and complex deployment sequence ever attempted in space. Once commissioning is complete, we will see awe-inspiring images that will capture our imagination."

The telescope's revolutionary technology will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, to everything in between. Webb will reveal new and unexpected discoveries and help humanity understand the origins of the universe and our place in it.

NASA Headquarters oversees the mission for the agency's Science Mission Directorate. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency's Johnson Space Center in Houston, Jet Propulsion Laboratory in Southern California, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in California's Silicon Valley, and others.

 

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Figure 3: The James Webb Space Telescope lifted off on an Ariane 5 rocket from Europe's Spaceport in French Guiana, at 13:20 CET on 25 December on its exciting mission to unlock the secrets of the Universe (image credit: ESA/CNES/Arianespace)

 

Figure 4: Highlights of the launch campaign for the James Webb Space Telescope, from its arrival at Europe's Spaceport in Kourou, French Guiana, weeks of launch preparations, to launch on board an Ariane 5, and separation of the spacecraft and solar panel deployment (video credit: ESA/CNES/Arianespace) 17)

 

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).

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Figure 5: 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].

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Figure 6: Overview of JWST trajectory to L2 (image credit: NASA)

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Figure 7: 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: 18)

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. 19)

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Figure 8: Deployment sequence of the OTE (image credit: NASA, STScI)

 

 


 

JWST mission status

• July 12, 2022: The dawn of a new era in astronomy is here as the world gets its first look at the full capabilities of NASA's James Webb Space Telescope, a partnership with ESA (European Space Agency) and CSA (Canadian Space Agency). 20) 21)

- "Today, we present humanity with a groundbreaking new view of the cosmos from the James Webb Space Telescope – a view the world has never seen before," said NASA Administrator Bill Nelson. "These images, including the deepest infrared view of our universe that has ever been taken, show us how Webb will help to uncover the answers to questions we don't even yet know to ask; questions that will help us better understand our universe and humanity's place within it.

- "The Webb team's incredible success is a reflection of what NASA does best. We take dreams and turn them into reality for the benefit of humanity. I can't wait to see the discoveries that we uncover – the team is just getting started!"

- NASA explores the unknown in space for the benefit of all, and Webb's first observations tell the story of the hidden universe through every phase of cosmic history – from neighboring planets outside our solar system, known as exoplanets, to the most distant observable galaxies in the early universe.

- "This is a singular and historic moment," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate. "It took decades of drive and perseverance to get us here, and I am immensely proud of the Webb team. These first images show us how much we can accomplish when we come together behind a shared goal, to solve the cosmic mysteries that connect us all. It's a stunning glimpse of the insights yet to come."

- "This is a singular and historic moment," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate. "It took decades of drive and perseverance to get us here, and I am immensely proud of the Webb team. These first images show us how much we can accomplish when we come together behind a shared goal, to solve the cosmic mysteries that connect us all. It's a stunning glimpse of the insights yet to come."

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Figure 9: One of the first images captured by the James Webb Space Telescope, this landscape of "mountains" and "valleys" speckled with glittering stars is actually the edge of a nearby young star-forming region called NGC 3324 in the Carina Nebula (image credits: NASA, ESA, CSA, and STScI)

Image description continued

- Called the Cosmic Cliffs, Webb's seemingly three-dimensional picture looks like craggy mountains on a moonlit evening. In reality, it is the edge of the giant, gaseous cavity within NGC 3324, and the tallest "peaks" in this image are about 7 light-years high. The cavernous area has been carved from the nebula by the intense ultraviolet radiation and stellar winds from extremely massive, hot, young stars located in the center of the bubble, above the area shown in this image.

- The blistering, ultraviolet radiation from the young stars is sculpting the nebula's wall by slowly eroding it away. Dramatic pillars tower above the glowing wall of gas, resisting this radiation. The "steam" that appears to rise from the celestial "mountains" is actually hot, ionized gas and hot dust streaming away from the nebula due to the relentless radiation.

- Webb reveals emerging stellar nurseries and individual stars that are completely hidden in visible-light pictures. Because of Webb's sensitivity to infrared light, it can peer through cosmic dust to see these objects. Protostellar jets, which emerge clearly in this image, shoot out from some of these young stars. The youngest sources appear as red dots in the dark, dusty region of the cloud. Objects in the earliest, rapid phases of star formation are difficult to capture, but Webb's extreme sensitivity, spatial resolution, and imaging capability can chronicle these elusive events.

- These observations of NGC 3324 will shed light on the process of star formation. Star birth propagates over time, triggered by the expansion of the eroding cavity. As the bright, ionized rim moves into the nebula, it slowly pushes into the gas and dust. If the rim encounters any unstable material, the increased pressure will trigger the material to collapse and form new stars.

- Conversely, this type of disturbance may also prevent star formation as the star-making material is eroded away. This is a very delicate balance between sparking star formation and stopping it. Webb will address some of the great, open questions of modern astrophysics: What determines the number of stars that form in a certain region? Why do stars form with a certain mass?

- Webb will also reveal the impact of star formation on the evolution of gigantic clouds of gas and dust. While the effect of massive stars – with their violent winds and high energy – is often apparent, less is known about the influence of the more numerous low-mass stars. As they form, these smaller stars create narrow, opposing jets seen here, which can inject a lot of momentum and energy into the clouds. This reduces the fraction of nebular material that seeds new stars.

- Up to this point, scientists have had very little data about the influence of the multitude of young and more energetic low-mass stars. With Webb, they will be able to obtain a full census of their number and impact throughout the nebula.

- Located roughly 7,600 light-years away, NGC 3324 was imaged by Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).

- NIRCam – with its crisp resolution and unparalleled sensitivity – unveils hundreds of previously hidden stars, and even numerous background galaxies.

- In MIRI's view, young stars and their dusty, planet-forming disks shine brightly in the mid-infrared, appearing pink and red. MIRI reveals structures that are embedded in the dust and uncovers the stellar sources of massive jets and outflows. With MIRI, the hot dust, hydrocarbons, and other chemical compounds on the surface of the ridges glow, giving the appearance of jagged rocks.

- NGC 3324 was first catalogued by James Dunlop in 1826. Visible from the Southern Hemisphere, it is located at the northwest corner of the Carina Nebula (NGC 3372), which resides in the constellation Carina. The Carina Nebula is home to the Keyhole Nebula and the active, unstable supergiant star called Eta Carinae.

• July 12, 2022: NASA's James Webb Space Telescope has cast the Southern Ring Nebula in an entirely new light. By observing the nebula in mid-infrared wavelengths, Webb has unveiled the second, dusty star at the center of the nebula in far more detail. The star closely orbits its companion as it periodically ejects layers of gas and dust. Together, the swirling duo have created a fantastic landscape of asymmetrical shells. Webb's near-infrared light image hones in on "spotlights" from the stars, where light travels through holes in the nebula's dusty ejections. 22) 23)

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Figure 10: Southern Ring Nebula (NIRCam and MIRI Images Side by Side), image credits: NASA, ESA, CSA, STScI

Some stars save the best for last.

- The dimmer star at the center of this scene has been sending out rings of gas and dust for thousands of years in all directions, and NASA's James Webb Space Telescope has revealed for the first time that this star is cloaked in dust.

- Two cameras aboard Webb captured the latest image of this planetary nebula, cataloged as NGC 3132, and known informally as the Southern Ring Nebula. It is approximately 2,500 light-years away.

- Webb will allow astronomers to dig into many more specifics about planetary nebulae like this one – clouds of gas and dust expelled by dying stars. Understanding which molecules are present, and where they lie throughout the shells of gas and dust will help researchers refine their knowledge of these objects.

- This observation shows the Southern Ring Nebula almost face-on, but if we could rotate it to view it edge-on, its three-dimensional shape would more clearly look like two bowls placed together at the bottom, opening away from one another with a large hole at the center.

- Two stars, which are locked in a tight orbit, shape the local landscape. Webb's infrared images feature new details in this complex system. The stars – and their layers of light – are prominent in the image from Webb's Near-Infrared Camera (NIRCam) on the left, while the image from Webb's Mid-Infrared Instrument (MIRI) on the right shows for the first time that the second star is surrounded by dust. The brighter star is in an earlier stage of its stellar evolution and will probably eject its own planetary nebula in the future.

- In the meantime, the brighter star influences the nebula's appearance. As the pair continues to orbit one another, they "stir the pot" of gas and dust, causing asymmetrical patterns.

- Each shell represents an episode where the fainter star lost some of its mass. The widest shells of gas toward the outer areas of the image were ejected earlier. Those closest to the star are the most recent. Tracing these ejections allows researchers to look into the history of the system.

- Observations taken with NIRCam also reveal extremely fine rays of light around the planetary nebula. Starlight from the central stars streams out where there are holes in the gas and dust – like sunlight through gaps in a cloud.

- Since planetary nebulae exist for tens of thousands of years, observing the nebula is like watching a movie in exceptionally slow motion. Each shell the star puffed off gives researchers the ability to precisely measure the gas and dust that are present within it.

- As the star ejects shells of material, dust and molecules form within them – changing the landscape even as the star continues to expel material. This dust will eventually enrich the areas around it, expanding into what's known as the interstellar medium. And since it's very long-lived, the dust may end up traveling through space for billions of years and become incorporated into a new star or planet.

- In thousands of years, these delicate layers of gas and dust will dissipate into surrounding space.

- NASA Headquarters oversees the mission for the agency's Science Mission Directorate. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency's Johnson Space Center in Houston, Jet Propulsion Laboratory in Southern California, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in California's Silicon Valley, and others.

- NIRCam was built by a team at the University of Arizona and Lockheed Martin's Advanced Technology Center.

- MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

• On Monday, 11 July 2022, President Joe Biden released one of the James Webb Space Telescope's first images in a preview event at the White House in Washington. NASA, in partnership with ESA (European Space Agency) and CSA (Canadian Space Agency), will release the full set of Webb's first full-color images and spectroscopic data during a televised broadcast beginning at 10:30 a.m. EDT (14:30 UTC) on Tuesday, July 12, from NASA's Goddard Space Flight Center in Greenbelt, Maryland. 24) 25)

- This first image from NASA's James Webb Space Telescope is the deepest and sharpest infrared image of the distant universe to date. Known as Webb's First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail. Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb's view for the first time. This slice of the vast universe covers a patch of sky approximately the size of a grain of sand held at arm's length by someone on the ground.

- This deep field, taken by Webb's Near-Infrared Camera (NIRCam), is a composite made from images at different wavelengths, totaling 12.5 hours – achieving depths at infrared wavelengths beyond the Hubble Space Telescope's deepest fields, which took weeks.

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Figure 11: The image shows the galaxy cluster SMACS 0723 as it appeared 4.6 billion years ago. The combined mass of this galaxy cluster acts as a gravitational lens, magnifying much more distant galaxies behind it. Webb's NIRCam has brought those distant galaxies into sharp focus – they have tiny, faint structures that have never been seen before, including star clusters and diffuse features. Researchers will soon begin to learn more about the galaxies' masses, ages, histories, and compositions, as Webb seeks the earliest galaxies in the universe (image credit: NASA, ESA, CSA, and STScI)

• July 12, 2022: Stephan's Quintet, a visual grouping of five galaxies, is best known for being prominently featured in the holiday classic film, "It's a Wonderful Life." Today, NASA's James Webb Space Telescope reveals Stephan's Quintet in a new light. This enormous mosaic is Webb's largest image to date, covering about one-fifth of the Moon's diameter. It contains over 150 million pixels and is constructed from almost 1,000 separate image files. The information from Webb provides new insights into how galactic interactions may have driven galaxy evolution in the early universe. 26) 27)

- With its powerful, infrared vision and extremely high spatial resolution, Webb shows never-before-seen details in this galaxy group. Sparkling clusters of millions of young stars and starburst regions of fresh star birth grace the image. Sweeping tails of gas, dust and stars are being pulled from several of the galaxies due to gravitational interactions. Most dramatically, Webb captures huge shock waves as one of the galaxies, NGC 7318B, smashes through the cluster.

- Together, the five galaxies of Stephan's Quintet are also known as the Hickson Compact Group 92 (HCG 92). Although called a "quintet," only four of the galaxies are truly close together and caught up in a cosmic dance. The fifth and leftmost galaxy, called NGC 7320, is well in the foreground compared with the other four. NGC 7320 resides 40 million light-years from Earth, while the other four galaxies (NGC 7317, NGC 7318A, NGC 7318B, and NGC 7319) are about 290 million light-years away. This is still fairly close in cosmic terms, compared with more distant galaxies billions of light-years away. Studying such relatively nearby galaxies like these helps scientists better understand structures seen in a much more distant universe.

- This proximity provides astronomers a ringside seat for witnessing the merging and interactions between galaxies that are so crucial to all of galaxy evolution. Rarely do scientists see in so much detail how interacting galaxies trigger star formation in each other, and how the gas in these galaxies is being disturbed. Stephan's Quintet is a fantastic "laboratory" for studying these processes fundamental to all galaxies.

- Tight groups like this may have been more common in the early universe when their superheated, infalling material may have fueled very energetic black holes called quasars. Even today, the topmost galaxy in the group – NGC 7319 – harbors an active galactic nucleus, a supermassive black hole 24 million times the mass of the Sun. It is actively pulling in material and puts out light energy equivalent to 40 billion Suns.

- Webb studied the active galactic nucleus in great detail with the Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI). These instruments' integral field units (IFUs) – which are a combination of a camera and spectrograph – provided the Webb team with a "data cube," or collection of images of the galactic core's spectral features.

- Much like medical magnetic resonance imaging (MRI), the IFUs allow scientists to "slice and dice" the information into many images for detailed study. Webb pierced through the shroud of dust surrounding the nucleus to reveal hot gas near the active black hole and measure the velocity of bright outflows. The telescope saw these outflows driven by the black hole in a level of detail never seen before.

- In NGC 7320, the leftmost and closest galaxy in the visual grouping, Webb was able to resolve individual stars and even the galaxy's bright core.

- As a bonus, Webb revealed a vast sea of thousands of distant background galaxies reminiscent of Hubble's Deep Fields.

- Combined with the most detailed infrared image ever of Stephan's Quintet from MIRI and the Near-Infrared Camera (NIRCam), the data from Webb will provide a bounty of valuable, new information. For example, it will help scientists understand the rate at which supermassive black holes feed and grow. Webb also sees star-forming regions much more directly, and it is able to examine emission from the dust – a level of detail impossible to obtain until now.

- Located in the constellation Pegasus, Stephan's Quintet was discovered by the French astronomer Édouard Stephan in 1877.

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Figure 12: In an enormous new image, NASA's James Webb Space Telescope reveals never-before-seen details of galaxy group "Stephan's Quintet". he close proximity of Stephan's Quintet gives astronomers a ringside seat to galactic mergers, interactions (image credit: NASA, ESA, CSA, and STScI)

• July 12, 2022: NASA's James Webb Space Telescope has captured the distinct signature of water, along with evidence for clouds and haze, in the atmosphere surrounding a hot, puffy gas giant planet orbiting a distant Sun-like star. 28) 29)

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Figure 13: Webb's enormous mirror, precise instruments joined forces to capture most detailed measurements of starlight filtering through atmosphere of a planet outside our solar system to date. The spectrum of light – which contains information about the makeup of a planetary atmosphere 1,150 light-years away – reveals distinct signature of water. The strength of the signal that Webb detected hints at the significant role the telescope will play in the search for potentially habitable planets in coming years. Webb's powerful new view also shows evidence of haze and clouds that previous studies of this planet did not detect (image credit: NASA, ESA, CSA, and STScI)

- The observation, which reveals the presence of specific gas molecules based on tiny decreases in the brightness of precise colors of light, is the most detailed of its kind to date, demonstrating Webb's unprecedented ability to analyze atmospheres hundreds of light-years away.

- While the Hubble Space Telescope has analyzed numerous exoplanet atmospheres over the past two decades, capturing the first clear detection of water in 2013, Webb's immediate and more detailed observation marks a giant leap forward in the quest to characterize potentially habitable planets beyond Earth.

- WASP-96 b is one of more than 5,000 confirmed exoplanets in the Milky Way. Located roughly 1,150 light-years away in the southern-sky constellation Phoenix, it represents a type of gas giant that has no direct analog in our solar system. With a mass less than half that of Jupiter and a diameter 1.2 times greater, WASP-96 b is much puffier than any planet orbiting our Sun. And with a temperature greater than 1000°F, it is significantly hotter. WASP-96 b orbits extremely close to its Sun-like star, just one-ninth of the distance between Mercury and the Sun, completing one circuit every 3½ Earth-days.

- The combination of large size, short orbital period, puffy atmosphere, and lack of contaminating light from objects nearby in the sky makes WASP-96 b an ideal target for atmospheric observations.

- On June 21, Webb's Near-Infrared Imager and Slitless Spectrograph (NIRISS) measured light from the WASP-96 system for 6.4 hours as the planet moved across the star. The result is a light curve showing the overall dimming of starlight during the transit, and a transmission spectrum revealing the brightness change of individual wavelengths of infrared light between 0.6 and 2.8 µm.

- While the light curve confirms properties of the planet that had already been determined from other observations – the existence, size, and orbit of the planet – the transmission spectrum reveals previously hidden details of the atmosphere: the unambiguous signature of water, indications of haze, and evidence of clouds that were thought not to exist based on prior observations.

- A transmission spectrum is made by comparing starlight filtered through a planet's atmosphere as it moves across the star to the unfiltered starlight detected when the planet is beside the star. Researchers are able to detect and measure the abundances of key gases in a planet's atmosphere based on the absorption pattern – the locations and heights of peaks on the graph. In the same way that people have distinctive fingerprints and DNA sequences, atoms and molecules have characteristic patterns of wavelengths that they absorb.

- The spectrum of WASP-96 b captured by NIRISS is not only the most detailed near-infrared transmission spectrum of an exoplanet atmosphere captured to date, but it also covers a remarkably wide range of wavelengths, including visible red light and a portion of the spectrum that has not previously been accessible from other telescopes (wavelengths longer than 1.6 microns). This part of the spectrum is particularly sensitive to water as well as other key molecules like oxygen, methane, and carbon dioxide, which are not immediately obvious in the WASP-96 b spectrum but which should be detectable in other exoplanets planned for observation by Webb.

- Researchers will be able to use the spectrum to measure the amount of water vapor in the atmosphere, constrain the abundance of various elements like carbon and oxygen, and estimate the temperature of the atmosphere with depth. They can then use this information to make inferences about the overall make-up of the planet, as well as how, when, and where it formed. The blue line on the graph is a best-fit model that takes into account the data, the known properties of WASP-96 b and its star (e.g., size, mass, temperature), and assumed characteristics of the atmosphere.

- The exceptional detail and clarity of these measurements is possible because of Webb's state-of-the-art design. Its 270-square-foot gold-coated mirror collects infrared light efficiently. Its precision spectrographs spread light out into rainbows of thousands of infrared colors. And its sensitive infrared detectors measure extremely subtle differences in brightness. NIRISS is able to detect color differences of only about one thousandth of a micron (the difference between green and yellow is about 50 microns), and differences in the brightness between those colors of a few hundred parts per million.

- In addition, Webb's extreme stability and its orbital location around Lagrange Point 2 roughly a million miles away from the contaminating effects of Earth's atmosphere makes for an uninterrupted view and clean data that can be analyzed relatively quickly.

- The extraordinarily detailed spectrum – made by simultaneously analyzing 280 individual spectra captured over the observation – provides just a hint of what Webb has in store for exoplanet research. Over the coming year, researchers will use spectroscopy to analyze the surfaces and atmospheres of several dozen exoplanets, from small rocky planets to gas- and ice-rich giants. Nearly one-quarter of Webb's Cycle 1 observation time is allocated to studying exoplanets and the materials that form them.

- This NIRISS observation demonstrates that Webb has the power to characterize the atmospheres of exoplanets—including those of potentially habitable planets—in exquisite detail.

• July 8, 2022: NASA's James Webb Space Telescope, a partnership with ESA (European Space Agency) and CSA (Canadian Space Agency), will soon reveal unprecedented and detailed views of the universe with the upcoming release of its first full-color images and spectroscopic data. 30)

- The images will include some taken by Webb's MIRI instrument, which is managed by the Jet Propulsion Laboratory for NASA.

- Below is the list of cosmic objects that Webb targeted for these first observations, which will be released in NASA's live broadcast beginning at 10:30 a.m. EDT (7:30 a.m. PDT) Tuesday, July 12. Each image will simultaneously be made available on social media as well as on the agency's website.

- These listed targets below represent the first wave of full-color scientific images and spectra the observatory has gathered, and the official beginning of Webb's general science operations. They were selected by an international committee of representatives from NASA, ESA, CSA, and the Space Telescope Science Institute.

a) Carina Nebula: The Carina Nebula is one of the largest and brightest nebulae in the sky, located approximately 7,600 light-years away in the southern constellation Carina. Nebulae are stellar nurseries where stars form. The Carina Nebula is home to many massive stars several times larger than the Sun.

b) WASP-96b (spectrum): WASP-96b is a giant planet outside our solar system, composed mainly of gas. The planet, located nearly 1,150 light-years from Earth, orbits its star every 3.4 days. It has about half the mass of Jupiter, and its discovery was announced in 2014.

c) Southern Ring Nebula: The Southern Ring, or "Eight-Burst" nebula, is a planetary nebula – an expanding cloud of gas surrounding a dying star. It is nearly half a light-year in diameter and is located approximately 2,000 light-years away from Earth.

d) Stephan's Quintet: About 290 million light-years away, Stephan's Quintet is located in the constellation Pegasus. It is notable for being the first compact galaxy group ever discovered in 1787. Four of the five galaxies within the quintet are locked in a cosmic dance of repeated close encounters.

e) SMACS 0723: Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a deep field view into both the extremely distant and intrinsically faint galaxy populations.

- The release of these first images marks the official beginning of Webb's science operations, which will continue to explore the mission's key science themes. Teams have already applied through a competitive process for time to use the telescope, in what astronomers call its first "cycle," or first year of observations.

- More information on how to join NASA for the release of Webb's first images is available online. For more about Webb's status, visit the "Where Is Webb?" tracker.

- The James Webb Space Telescope is the world's premier space science observatory. 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.

• July 7, 2022: Three of the four science instruments on NASA's James Webb Space Telescope have completed their commissioning activities and are ready for science. 31)

- Each of Webb's instruments has multiple modes of operation, which need to be tested, calibrated, and ultimately verified before they can begin to conduct science. The latest instrument to complete this process, the Near-Infrared Spectrograph (NIRSpec), has four key modes the team officially confirmed as ready to go.

- "We made it: NIRSpec is ready for science! This is an amazing moment, the result of the hard work of so many JWST and NIRSpec people and teams over more than two decades. I am just so proud of everyone," said Pierre Ferruit, Webb project scientist with ESA (European Space Agency) and principal investigator for NIRSpec. "Now is time for science, and I am eager to see the first scientific results coming from NIRSpec observations. I have no doubt they will be fantastic. Big thanks to all who made this possible across the years – great job!"

- The final mode verified for NIRSpec was the multi-object spectroscopy mode, a key capability that allows Webb to capture spectra, or rainbows of infrared light, from hundreds of different cosmic targets at once. In multi-object spectroscopy mode, NIRSpec can individually open and close about 250,000 small shutters, all just the width of a human hair, to view some portions of the sky while blocking others. By controlling this "microshutter array," Webb can observe multiple specific targets while reducing interference from others.

- The confirmation of NIRSpec's multi-object spectroscopy mode marks the first time this capability has been verified for use from space. It will allow NIRSpec to characterize everything from the faintest objects in the universe to the formation of galaxies and star clusters.

- NIRSpec was built for ESA by a consortium of European companies led by Airbus Defence and Space, with NASA's Goddard Space Flight Center in Greenbelt, Maryland, providing its detector and microshutter subsystems.

- Out of 17 total instrument modes across Webb's four instruments, only one mode remains to be verified, for the Near-Infrared Camera (NIRCam). When the team confirms this remaining mode, the months-long process of preparing Webb for science will formally be complete.

- Webb's commissioning process culminates on July 12, with the release of the telescope's first full-color images and spectroscopic data, and the official beginning of its science mission.

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Figure 14: This commissioning test image is a subset of a NIRSpec multi-object spectroscopy exposure of a region close to the center of our Milky Way galaxy. NIRSpec's two detectors and its microshutter arrays were used to pack more than 200 spectra in a single exposure. Each horizontal stripe is a spectrum that scientists will be able to analyze to better understand the composition and properties of the gas found between the stars in this region – for example, through the study of emission lines that show up at small, brighter, slightly tilted vertical lines in these spectra. Credit: NASA/ESA/CSA and the NIRSpec team

• July 6, 2022: We are less than one week away from the release of the first full-color images from NASA's James Webb Space Telescope, but how does the observatory find and lock onto its targets? Webb's Fine Guidance Sensor (FGS) – developed by the Canadian Space Agency – was designed with this particular question in mind. Recently it captured a view of stars and galaxies that provides a tantalizing glimpse at what the telescope's science instruments will reveal in the coming weeks, months, and years. 32)

- FGS has always been capable of capturing imagery, but its primary purpose is to enable accurate science measurements and imaging with precision pointing. When it does capture imagery, the imagery is typically not kept: Given the limited communications bandwidth between L2 and Earth, Webb only sends data from up to two science instruments at a time. But during a week-long stability test in May, it occurred to the team that they could keep the imagery that was being captured because there was available data transfer bandwidth.

- The resulting engineering test image has some rough-around-the-edges qualities to it. It was not optimized to be a science observation; rather, the data was taken to test how well the telescope could stay locked onto a target, but it does hint at the power of the telescope. It carries a few hallmarks of the views Webb has produced during its postlaunch preparations. Bright stars stand out with their six, long, sharply defined diffraction spikes – an effect due to Webb's six-sided mirror segments. Beyond the stars, galaxies fill nearly the entire background.

- The result – using 72 exposures over 32 hours – is among the deepest images of the universe ever taken, according to Webb scientists. When FGS' aperture is open, it is not using color filters like the other science instruments – meaning it is impossible to study the age of the galaxies in this image with the rigor needed for scientific analysis. But even when capturing unplanned imagery during a test, FGS is capable of producing stunning views of the cosmos.

- "With the Webb telescope achieving better-than-expected image quality, early in commissioning we intentionally defocused the guiders by a small amount to help ensure they met their performance requirements. When this image was taken, I was thrilled to clearly see all the detailed structure in these faint galaxies. Given what we now know is possible with deep broad-band guider images, perhaps such images, taken in parallel with other observations where feasible, could prove scientifically useful in the future," said Neil Rowlands, program scientist for Webb's Fine Guidance Sensor, at Honeywell Aerospace.

- Because this image was not created with a science result in mind, there are a few features that are quite different than the full-resolution images that will be released July 12. Those images will include what will be – for a short time at least – the deepest image of the universe ever captured, as NASA Administrator Bill Nelson announced on June 29.

- The FGS image is colored using the same reddish color scheme that has been applied to Webb's other engineering images throughout commissioning. In addition, there was no "dithering" during these exposures. Dithering is when the telescope repositions slightly between each exposure. In addition, the centers of bright stars appear black because they saturate Webb's detectors, and the pointing of the telescope didn't change over the exposures to capture the center from different pixels within the camera's detectors. The overlapping frames of the different exposures can also be seen at the image's edges and corners.

- In this engineering test, the purpose was to lock onto one star and to test how well Webb could control its "roll" – literally, Webb's ability to roll to one side like an aircraft in flight. That test was performed successfully – in addition to producing an image that sparks the imagination of scientists who will be analyzing Webb's science data, said Jane Rigby, Webb's operations scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

- "The faintest blobs in this image are exactly the types of faint galaxies that Webb will study in its first year of science operations," Rigby said.

- While Webb's four science instruments will ultimately reveal the telescope's new view of the universe, the Fine Guidance Sensor is the one instrument that will be used in every single Webb observation over the course of the mission's lifetime. FGS has already played a crucial role in aligning Webb's optics. Now, during the first real science observations made in June and once science operations begin in mid-July, it will guide each Webb observation to its target and maintain the precision necessary for Webb to produce breakthrough discoveries about stars, exoplanets, galaxies, and even moving targets within our solar system.

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Figure 15: This Fine Guidance Sensor test image was acquired in parallel with NIRCam imaging of the star HD147980 over a period of eight days at the beginning of May. This engineering image represents a total of 32 hours of exposure time at several overlapping pointings of the Guider 2 channel. The observations were not optimized for detection of faint objects, but nevertheless the image captures extremely faint objects and is, for now, the deepest image of the infrared sky. The unfiltered wavelength response of the guider, from 0.6 to 5 µm, helps provide this extreme sensitivity. The image is mono-chromatic and is displayed in false color with white-yellow-orange-red representing the progression from brightest to dimmest. The bright star (at 9.3 magnitude) on the right hand edge is 2MASS 16235798+2826079. There are only a handful of stars in this image – distinguished by their diffraction spikes. The rest of the objects are thousands of faint galaxies, some in the nearby universe, but many, many more in the distant universe (image credits: NASA, CSA, and FGS team)

• June 22, 2022: Two research teams will use the telescope's powerful instruments to capture and characterize some of the earliest galaxies in the universe. 33)

- The universe was a very different place for several hundred million years after the big bang. It wasn't yet transparent like it is today – neutral gas made it semi-opaque. This is a period when the first galaxies in the universe were beginning to form. Telescopes have spotted many distant galaxies – but none earlier than 400 million years after the big bang. What were galaxies that existed even earlier like? Two research teams using the James Webb Space Telescope will wield its state-of-the-art instruments to reveal an untold number of details about this early period in the universe for the first time – and revise what we know about some of the earliest chapters of galaxy evolution.

- For decades, telescopes have helped us capture light from galaxies that formed as far back as 400 million years after the big bang – incredibly early in the context of the universe's 13.8-billion-year history. But what were galaxies like that existed even earlier, when the universe was semi-transparent at the beginning of a period known as the Era of Reionization? NASA's next flagship observatory, the James Webb Space Telescope, is poised to add new riches to our wealth of knowledge not only by capturing images from galaxies that existed as early as the first few hundred million years after the big bang, but also by giving us detailed data known as spectra. With Webb's observations, researchers will be able to tell us about the makeup and composition of individual galaxies in the early universe for the first time.

- The Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey, co-led by Steven L. Finkelstein, an associate professor at the University of Texas at Austin, will target the same two regions that make up the Hubble Ultra Deep Field – locations in the constellation Fornax where Hubble spent more than 11 days taking deep exposures. To produce its observations, the Hubble Space Telescope targeted nearby areas of the sky simultaneously with two instruments – slightly offset from one another – known as a primary and a parallel field. "We have the same advantage with Webb," Finkelstein explained. "We're using two science instruments at once, and they will observe continuously." They will point Webb's Near-Infrared Imager and Slitless Spectrograph (NIRISS) on the primary Hubble Ultra Deep Field, and Webb's Near-Infrared Camera (NIRCam) on the parallel field, getting twice the bang for their "buck" of telescope time.

- For the imaging with NIRCam, they'll observe for over 125 hours. With each passing minute, they'll obtain more and more information from deeper and deeper in the universe. What do they seek? Some of the earliest galaxies that formed. "We have really good indications from Hubble that there are galaxies in place at a time 400 million years after the big bang," Finkelstein said. "The ones we see with Hubble are pretty big and very bright. It's highly likely there are smaller, fainter galaxies that formed even earlier that are waiting to be found."

- This program will use only about one-third of the time Hubble has spent to date on similar investigations. Why? In part, this is because Webb's instruments were designed to capture infrared light. As light travels through space toward us, it stretches into longer, redder wavelengths due to the expansion of the universe. "Webb will help us push all the boundaries," said Jennifer Lotz, a coinvestigator on the proposal and director of the Gemini Observatory, part of the National Science Foundation's NOIRLab (National Optical-Infrared Astronomy Research Laboratory). "And we're going to release the data immediately to benefit all researchers."

- These researchers will also focus on identifying the metal content in each galaxy, especially in smaller and dimmer galaxies that haven't yet been thoroughly examined – specifically with the spectra Webb's NIRISS instrument delivers. "One of the fundamental ways that we trace evolution across cosmic time is by the amount of metals that are in a galaxy," explained Danielle Berg, an assistant professor at the University of Texas at Austin and a co-investigator on the proposal. When the universe began, there was only hydrogen and helium. New elements were formed by successive generations of stars. By cataloging the contents of each galaxy, the researchers will be able to plot out precisely when various elements existed and update models that project how galaxies evolved in the early universe.

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Figure 16: This Hubble Space Telescope image, known as the Hubble Ultra Deep Field, reveals about 10,000 galaxies and combines ultraviolet, visible, and near-infrared light. Two programs that will use the James Webb Space Telescope will add more detail to this image, capturing thousands of additional galaxies in a fuller range of infrared light. Webb will return both imagery and data known as spectra, providing more details about some of the earliest galaxies to exist in the universe for the first time [image credits: Science: NASA, ESA, Steven V.W. Beckwith (STScI), HUDF Team (STScI)]

 

Figure 17: Take a trip through time and space to the early universe with NASA's James Webb Space Telescope. How will Webb reveal the never-before-seen first galaxies? What are astronomers looking for? Discover the answers to these questions and more with this video [video credits: NASA, ESA, CSA, Danielle Kirshenblat (STScI)]

Peeling Back New Layers

- Another program, led by Michael Maseda, an assistant professor at the University of Wisconsin-Madison, will examine the primary Hubble Ultra Deep Field using the microshutter array within Webb's Near-Infrared Spectrograph (NIRSpec). This instrument returns spectra for specific objects depending on which miniature shutters researchers open. "These galaxies existed during the first billion years in the history of the universe, which we have very little information about to date," Maseda explained. "Webb will provide the first large sample that will give us the chance to understand them in detail."

- We know these galaxies exist because of extensive observations this team has made – along with an international research team – with the ground-based Very Large Telescope's Multi Unit Spectroscopic Explorer (MUSE) instrument. Although MUSE is the "scout," identifying smaller, fainter galaxies in this deep field, Webb will be the first telescope to fully characterize their chemical compositions.

- These extremely distant galaxies have important implications for our understanding of how galaxies formed in the early universe. "Webb will open a new space for discovery," explained Anna Feltre, a research fellow at the National Institute for Astrophysics in Italy and a co-investigator. "Its data will help us learn precisely what happens as a galaxy forms, including which metals they contain, how quickly they grow, and if they already have black holes."

- This research will be conducted as part of Webb's General Observer (GO) programs, which are competitively selected using a dual-anonymous review, the same system that is used to allocate time on the Hubble Space Telescope.

• June 1, 2022: NASA's James Webb Space Telescope, a partnership with ESA (European Space Agency) and the Canadian Space Agency (CSA), will release its first full-color images and spectroscopic data on July 12, 2022. As the largest and most complex observatory ever launched into space, Webb has been going through a six-month period of preparation before it can begin science work, calibrating its instruments to its space environment and aligning its mirrors. This careful process, not to mention years of new technology development and mission planning, has built up to the first images and data: a demonstration of Webb at its full power, ready to begin its science mission and unfold the infrared universe. 34)

- "As we near the end of preparing the observatory for science, we are on the precipice of an incredibly exciting period of discovery about our universe. The release of Webb's first full-color images will offer a unique moment for us all to stop and marvel at a view humanity has never seen before," said Eric Smith, Webb program scientist at NASA Headquarters in Washington. "These images will be the culmination of decades of dedication, talent, and dreams – but they will also be just the beginning."

Behind the Scenes: Creating Webb's First Images

- Deciding what Webb should look at first has been a project more than five years in the making, undertaken by an international partnership between NASA, ESA, CSA, and the Space Telescope Science Institute (STScI) in Baltimore, home to Webb's science and mission operations.

- "Our goals for Webb's first images and data are both to showcase the telescope's powerful instruments and to preview the science mission to come," said astronomer Klaus Pontoppidan, Webb project scientist at STScI. "They are sure to deliver a long-awaited ‘wow' for astronomers and the public."

- Once each of Webb's instruments has been calibrated, tested, and given the green light by its science and engineering teams, the first images and spectroscopic observations will be made. The team will proceed through a list of targets that have been preselected and prioritized by an international committee to exercise Webb's powerful capabilities. Then the production team will receive the data from Webb's instrument scientists and process it into images for astronomers and the public.

- "I feel very privileged to be a part of it," said Alyssa Pagan, a science visuals developer at STScI. "Typically, the process from raw telescope data to final, clean image that communicates scientific information about the universe can take anywhere from weeks to a month," Pagan said.

What Will We See?

- While careful planning for Webb's first full-color images has been underway for a long time, the new telescope is so powerful that it is difficult to predict exactly how the first images will look. "Of course, there are things we are expecting and hoping to see, but with a new telescope and this new high-resolution infrared data, we just won't know until we see it," said STScI's lead science visuals developer Joseph DePasquale.

- Early alignment imagery has already demonstrated the unprecedented sharpness of Webb's infrared view. However, these new images will be the first in full color and the first to showcase Webb's full science capabilities. In addition to imagery, Webb will be capturing spectroscopic data – detailed information astronomers can read in light. The first images package of materials will highlight the science themes that inspired the mission and will be the focus of its work: the early universe, the evolution of galaxies through time, the lifecycle of stars, and other worlds. All of Webb's commissioning data – the data taken while aligning the telescope and preparing the instruments – will also be made publicly available.

What's Next?

- Science! After capturing its first images, Webb's scientific observations will begin, continuing to explore the mission's key science themes. Teams have already applied through a competitive process for time to use the telescope, in what astronomers call its first "cycle," or first year of observations. Observations are carefully scheduled to make the most efficient use of the telescope's time.

- These observations mark the official beginning of Webb's general science operations – the work it was designed to do. Astronomers will use Webb to observe the infrared universe, analyze the data collected, and publish scientific papers on their discoveries.

- Beyond what is already planned for Webb, there are the unexpected discoveries astronomers can't anticipate. One example: In 1990 when the Hubble Space Telescope launched, dark energy was completely unknown. Now it is one of the most exciting areas of astrophysics. What will Webb discover?

- The James Webb Space Telescope is the world's premier space science observatory. 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.

• May 26, 2022: Researchers will train Webb's high-precision spectrographs on two intriguing rocky exoplanets. 35)

- With its mirror segments beautifully aligned and its scientific instruments undergoing calibration, NASA's James Webb Space Telescope is just weeks away from full operation. Soon after the first observations are revealed this summer, Webb's in-depth science will begin.

- Among the investigations planned for the first year are studies of two hot exoplanets classified as "super-Earths" for their size and rocky composition: the lava-covered 55 Cancri e and the airless LHS 3844 b. Researchers will train Webb's high-precision spectrographs on these planets with a view to understanding the geologic diversity of planets across the galaxy, and the evolution of rocky planets like Earth.

Super-Hot Super-Earth 55 Cancri e

- 55 Cancri e orbits less than 1.5 million miles from its Sun-like star (one twenty-fifth of the distance between Mercury and the Sun), completing one circuit in less than 18 hours. With surface temperatures far above the melting point of typical rock-forming minerals, the day side of the planet is thought to be covered in oceans of lava.

- Planets that orbit this close to their star are assumed to be tidally locked, with one side facing the star at all times. As a result, the hottest spot on the planet should be the one that faces the star most directly, and the amount of heat coming from the day side should not change much over time.

- But this doesn't seem to be the case. Observations of 55 Cancri e from NASA's Spitzer Space Telescope suggest that the hottest region is offset from the part that faces the star most directly, while the total amount of heat detected from the day side does vary.

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Figure 18: The illustration is showing what exoplanet 55 Cancri e could look like, based on current understanding of the planet. 55 Cancri e is a rocky planet with a diameter almost twice that of Earth orbiting just 0.015 astronomical units from its Sun-like star. Because of its tight orbit, the planet is extremely hot, with dayside temperatures reaching 4,400º Fahrenheit (about 2,400º Celsius). Although previous studies have ruled out a thick hydrogen, carbon dioxide, or water atmosphere, it is possible that the planet has a substantial atmosphere made of oxygen or nitrogen, or a very thin atmosphere of mineral vapor, such as silicon oxide. - Researchers think that if the planet is tidally locked, the lit surface must be permanently molten. If the planet is not locked, it would experience day-night cycles, with the surface heating up and melting during the day, and cooling and solidifying at night. The extreme heat during the day would also cause some of the molten rock to vaporize, forming a very tenuous mineral vapor atmosphere. In the evening, this vapor would condense and fall as a rain of lava back onto the surface, where it would turn solid overnight. - Spectroscopic observations using Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) will help determine whether or not the planet has an atmosphere, and if so, what that atmosphere is made of. The observations will also help determine whether or not the planet is tidally locked [image credit: ARTWORK: NASA, ESA, CSA, Dani Player (STScI)]

Does 55 Cancri e Have a Thick Atmosphere?

- One explanation for these observations is that the planet has a dynamic atmosphere that moves heat around. "55 Cancri e could have a thick atmosphere dominated by oxygen or nitrogen," explained Renyu Hu of NASA's Jet Propulsion Laboratory in Southern California, who leads a team that will use Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) to capture the thermal emission spectrum of the day side of the planet. "If it has an atmosphere, [Webb] has the sensitivity and wavelength range to detect it and determine what it is made of," Hu added.

Or Is It Raining Lava in the Evening on 55 Cancri e?

- Another intriguing possibility, however, is that 55 Cancri e is not tidally locked. Instead, it may be like Mercury, rotating three times for every two orbits (what's known as a 3:2 resonance). As a result, the planet would have a day-night cycle.

- "That could explain why the hottest part of the planet is shifted," explained Alexis Brandeker, a researcher from Stockholm University who leads another team studying the planet. "Just like on Earth, it would take time for the surface to heat up. The hottest time of the day would be in the afternoon, not right at noon."

- Brandeker's team plans to test this hypothesis using NIRCam to measure the heat emitted from the lit side of 55 Cancri e during four different orbits. If the planet has a 3:2 resonance, they will observe each hemisphere twice and should be able to detect any difference between the hemispheres.

- In this scenario, the surface would heat up, melt, and even vaporize during the day, forming a very thin atmosphere that Webb could detect. In the evening, the vapor would cool and condense to form droplets of lava that would rain back to the surface, turning solid again as night falls.

Somewhat Cooler Super-Earth LHS 3844 b

- While 55 Cancri e will provide insight into the exotic geology of a world covered in lava, LHS 3844 b affords a unique opportunity to analyze the solid rock on an exoplanet surface.

- Like 55 Cancri e, LHS 3844 b orbits extremely close to its star, completing one revolution in 11 hours. However, because its star is relatively small and cool, the planet is not hot enough for the surface to be molten. Additionally, Spitzer observations indicate that the planet is very unlikely to have a substantial atmosphere.

What Is the Surface of LHS 3844 b Made of?

- While we won't be able to image the surface of LHS 3844 b directly with Webb, the lack of an obscuring atmosphere makes it possible to study the surface with spectroscopy.

- "It turns out that different types of rock have different spectra," explained Laura Kreidberg at the Max Planck Institute for Astronomy. "You can see with your eyes that granite is lighter in color than basalt. There are similar differences in the infrared light that rocks give off."

- Kreidberg's team will use MIRI to capture the thermal emission spectrum of the day side of LHS 3844 b, and then compare it to spectra of known rocks, like basalt and granite, to determine its composition. If the planet is volcanically active, the spectrum could also reveal the presence of trace amounts of volcanic gases.

- The importance of these observations goes far beyond just two of the more than 5,000 confirmed exoplanets in the galaxy. "They will give us fantastic new perspectives on Earth-like planets in general, helping us learn what the early Earth might have been like when it was hot like these planets are today," said Kreidberg.

- These observations of 55 Cancri e and LHS 3844 b will be conducted as part of Webb's Cycle 1 General Observers program. General Observers programs were competitively selected using a dual-anonymous review system, the same system used to allocate time on Hubble.

- The James Webb Space Telescope is the world's premier space science observatory. 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.

• May 9, 2022: The James Webb Space Telescope is aligned across all four of its science instruments, as seen in a previous engineering image showing the observatory's full field of view. Now, we take a closer look at that same image, focusing on Webb's coldest instrument: the Mid-Infrared Instrument (MIRI).

- For example, Webb's MIRI image shows the interstellar gas in unprecedented detail. Here, you can see the emission from ‘polycyclic aromatic hydrocarbons' – molecules of carbon and hydrogen that play an important role in the thermal balance and chemistry of interstellar gas. When Webb is ready to begin science observations, studies such as these with MIRI will help give astronomers new insights into the birth of stars and protoplanetary systems.

- In the meantime, the Webb team has begun the process of setting up and testing Webb's instruments to begin science observations this summer. Today at 17:00 CEST, Webb experts will preview these next two months of instrument preparations in a teleconference for media. Listen to the audio stream live at nasa.gov/live.

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Figure 19: MIRI and Spitzer comparison image. The MIRI test image (at 7.7 µm) shows part of the Large Magellanic Cloud. This small satellite galaxy of the Milky Way provided a dense star field to test Webb's performance. Here, a close-up of the MIRI image is compared to a past image of the same target taken with NASA's Spitzer Space Telescope's Infrared Array Camera (at 8.0 µm). The retired Spitzer was the first observatory to provide high-resolution images of the near- and mid-infrared Universe. Webb, by virtue of its significantly larger primary mirror and improved detectors, will allow us to see the infrared sky with improved clarity, enabling even more discoveries (image credit: Spitzer: NASA/JPL-Caltech; MIRI: NASA/ESA/CSA/STScI)

• May 5, 2022: NASA's James Webb Space Telescope is now experiencing all seasons – from hot to cold – as it undergoes the thermal stability test. Meanwhile, activities are underway for the final phase of commissioning: digging into the details of the science instruments, the heart of Webb. To complete commissioning, we will measure the detailed performance of the science instruments before we start routine science operations in the summer. 36)

- Today, the lead commissioning scientist for Webb, Scott Friedman of the Space Telescope Science Institute (STScI), gives us all the details on this final phase of commissioning.

- "With the telescope beautifully aligned and the observatory near its final cryogenic temperature, we are ready to begin the last group of activities before the science observations start: science instrument commissioning. Here I describe just a few of those activities.

- "The instruments, the Near-Infrared Camera (NIRCam), Near-Infrared Spectrometer (NIRSpec), Near-Infrared Imager and Slitless Spectrometer (NIRISS), Mid-Infrared Instrument (MIRI), and the Fine Guidance Sensor (FGS) have been powered up and safely cooled. We have operated their mechanisms and detectors, including filter wheels, grating wheels, and the NIRSpec microshutter assembly. The Webb optics team used images of isolated stars taken with each of the instruments to align the primary and secondary mirrors of the observatory. But we have more work to do before Webb is fully ready to embark on the ambitious science observations that will reveal the secrets of the universe.

- "We will now begin an extensive suite of calibrations and characterizations of the instruments using a rich variety of astronomical sources. We will measure the instruments' throughput – how much of the light that enters the telescope reaches the detectors and is recorded. There is always some loss with each reflection by the mirrors of the telescope and within each instrument, and no detector records every photon that arrives. We will measure this throughput at multiple wavelengths of light by observing standard stars whose light emission is known from data obtained with other observatories combined with theoretical calculations.

- "The astrometric calibration of each instrument maps the pixels on the detectors to the precise locations on the sky, to correct the small but unavoidable optical distortions that are present in every optical system. We do this by observing the Webb astrometric field, a small patch of sky in a nearby galaxy, the Large Magellanic Cloud. This field was observed by the Hubble Space Telescope to establish the coordinates of about 200,000 stars to an accuracy of 1 milliarcsec (less than 0.3 millionths of a degree). Calibrating this distortion is required to precisely place the science targets on the instruments' field of view. For example, to get the spectra of a hundred galaxies simultaneously using the NIRSpec microshutter assembly, the telescope must be pointed so that each galaxy is in the proper shutter, and there are a quarter of a million shutters!

- "We will also measure the sharpness of the stellar images, what astronomers call the ‘point spread function.' We already know the telescope is delivering to the instruments image quality that exceeds our prelaunch expectations, but each instrument has additional optics. These optics perform a function, such as passing the light through filters to get color information about the astronomical target or using a diffraction grating to spread the incoming light into its constituent colors. Measuring the point spread function within each instrument at different wavelengths provides an important calibration for interpreting the data.

- "We will test target acquisition for each instrument. For some observations, it is sufficient to point the telescope using the position of a guide star in the Fine Guidance Sensor and know the location of the science target relative to that guide star. This places the science target to an accuracy of a few tenths of an arcsecond. However, in some cases more precision is necessary, approximately a hundredth of an arcsecond. For example, for coronagraphy, the star has to be placed behind a mask so its light is blocked, allowing the nearby exoplanet to shine through. In time series observations, we measure how an exoplanet's atmosphere absorbs the stellar light during the hours it takes to pass in front of its star, allowing us to measure the properties and constituents of the planet's atmosphere. Both of these applications require that the instrument send corrections to the telescope pointing control system to put the science target precisely in the correct location within the instrument's field of view.

- "A final example of our instrument commissioning activities is observations of moving targets. Most astronomical objects are so far away that they appear to be stationary on the sky. However, this is not true of the planets, satellites and rings, asteroids, and comets within our own solar system. Observing these requires that the observatory change its pointing direction relative to the background guide stars during the observation. We will test this capability by observing asteroids of different apparent speeds using each instrument.

- "We are now in the last two months of Webb's commissioning before it is fully ready for its scientific mission. We still have important properties and capabilities of the instruments to test, measure, and demonstrate. When these are complete, we will be ready to begin the great science programs that astronomers and the public alike have been eagerly awaiting. We are almost there."

• April 28, 2022: Alignment of NASA's James Webb Space Telescope is now complete. After full review, the observatory has been confirmed to be capable of capturing crisp, well-focused images with each of its four powerful onboard science instruments. Upon completing the seventh and final stage of telescope alignment, the team held a set of key decision meetings and unanimously agreed that Webb is ready to move forward into its next and final series of preparations, known as science instrument commissioning. This process will take about two months before scientific operations begin in the summer. 37) 38)

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Figure 20: Engineering images of sharply focused stars in the field of view of each instrument demonstrate that the telescope is fully aligned and in focus. For this test, Webb pointed at part of the Large Magellanic Cloud, a small satellite galaxy of the Milky Way, providing a dense field of hundreds of thousands of stars across all the observatory's sensors. The sizes and positions of the images shown here depict the relative arrangement of each of Webb's instruments in the telescope's focal plane, each pointing at a slightly offset part of the sky relative to one another. Webb's three imaging instruments are NIRCam (images shown here at a wavelength of 2 µm), NIRISS (image shown here at 1.5 µm), and MIRI (shown at 7.7 µm, a longer wavelength revealing emission from interstellar clouds as well as starlight). NIRSpec is a spectrograph rather than imager but can take images, such as the 1.1 µm image shown here, for calibrations and target acquisition. The dark regions visible in parts of the NIRSpec data are due to structures of its microshutter array, which has several hundred thousand controllable shutters that can be opened or shut to select which light is sent into the spectrograph. Lastly, Webb's Fine Guidance Sensor tracks guide stars to point the observatory accurately and precisely; its two sensors are not generally used for scientific imaging but can take calibration images such as those shown here. This image data is used not just to assess image sharpness but also to precisely measure and calibrate subtle image distortions and alignments between sensors as part of Webb's overall instrument calibration process (image credit: NASA/STScI)

- The alignment of the telescope across all of Webb's instruments can be seen in a series of images that captures the observatory's full field of view.

- "These remarkable test images from a successfully aligned telescope demonstrate what people across countries and continents can achieve when there is a bold scientific vision to explore the universe," said Lee Feinberg, Webb optical telescope element manager at NASA's Goddard Space Flight Center.

- The optical performance of the telescope continues to be better than the engineering team's most optimistic predictions. Webb's mirrors are now directing fully focused light collected from space down into each instrument, and each instrument is successfully capturing images with the light being delivered to them. The image quality delivered to all instruments is "diffraction-limited," meaning that the fineness of detail that can be seen is as good as physically possible given the size of the telescope. From this point forward the only changes to the mirrors will be very small, periodic adjustments to the primary mirror segments.

- "With the completion of telescope alignment and half a lifetime's worth of effort, my role on the James Webb Space Telescope mission has come to an end," said Scott Acton, Webb wavefront sensing and controls scientist, Ball Aerospace. "These images have profoundly changed the way I see the universe. We are surrounded by a symphony of creation; there are galaxies everywhere! It is my hope that everyone in the world can see them."

- Now, the Webb team will turn its attention to science instrument commissioning. Each instrument is a highly sophisticated set of detectors equipped with unique lenses, masks, filters, and customized equipment that helps it perform the science it was designed to achieve. The specialized characteristics of these instruments will be configured and operated in various combinations during the instrument commissioning phase to fully confirm their readiness for science. With the formal conclusion of telescope alignment, key personnel involved with the commissioning of each instrument have arrived at the Mission Operations Center at the Space Telescope Science Institute in Baltimore, and some personnel involved with telescope alignment have concluded their duties.

 

Figure 21: Webb Telescope Completes Alignment Phase /video credit: (NASA's Goddard Space Flight Center)

- Though telescope alignment is complete, some telescope calibration activities remain: As part of scientific instrument commissioning, the telescope will be commanded to point to different areas in the sky where the total amount of solar radiation hitting the observatory will vary to confirm thermal stability when changing targets. Furthermore, ongoing maintenance observations every two days will monitor the mirror alignment and, when needed, apply corrections to keep the mirrors in their aligned locations.

• April 13, 2022: NASA's James Webb Space Telescope will see the first galaxies to form after the big bang, but to do that its instruments first need to get cold – really cold. On April 7, Webb's Mid-Infrared Instrument (MIRI) – a joint development by NASA and ESA (European Space Agency) – reached its final operating temperature below 7 kelvins (minus 447º Fahrenheit, or minus 266º Celsius). 39) 40)

- Along with Webb's three other instruments, MIRI initially cooled off in the shade of Webb's tennis-court-size sunshield, dropping to about 90 kelvins (minus 298º F, or minus 183º C). But dropping to less than 7 kelvins required an electrically powered cryocooler. Last week, the team passed a particularly challenging milestone called the "pinch point," when the instrument goes from 15 kelvins (minus 433º F, or minus 258º C) to 6.4 kelvins (minus 448º F, or minus 267º C).

- The low temperature is necessary because all four of Webb's instruments detect infrared light – wavelengths slightly longer than those that human eyes can see. Distant galaxies, stars hidden in cocoons of dust, and planets outside our solar system all emit infrared light. But so do other warm objects, including Webb's own electronics and optics hardware. Cooling down the four instruments' detectors and the surrounding hardware suppresses those infrared emissions. MIRI detects longer infrared wavelengths than the other three instruments, which means it needs to be even colder.

- Another reason Webb's detectors need to be cold is to suppress something called dark current, or electric current created by the vibration of atoms in the detectors themselves. Dark current mimics a true signal in the detectors, giving the false impression that they have been hit by light from an external source. Those false signals can drown out the real signals astronomers want to find. Since temperature is a measurement of how fast the atoms in the detector are vibrating, reducing the temperature means less vibration, which in turn means less dark current.

- MIRI's ability to detect longer infrared wavelengths also makes it more sensitive to dark current, so it needs to be colder than the other instruments to fully remove that effect. For every degree the instrument temperature goes up, the dark current goes up by a factor of about 10.

- Once MIRI reached a frigid 6.4 kelvins, scientists began a series of checks to make sure the detectors were operating as expected. Like a doctor searching for any sign of illness, the MIRI team looks at data describing the instrument's health, then gives the instrument a series of commands to see if it can execute tasks correctly. This milestone is the culmination of work by scientists and engineers at multiple institutions in addition to JPL, including Northrop Grumman, which built the cryocooler, and NASA's Goddard Space Flight Center, which oversaw the integration of MIRI and the cooler to the rest of the observatory.

- "We spent years practicing for that moment, running through the commands and the checks that we did on MIRI," said Mike Ressler, project scientist for MIRI at JPL. "It was kind of like a movie script: Everything we were supposed to do was written down and rehearsed. When the test data rolled in, I was ecstatic to see it looked exactly as expected and that we have a healthy instrument."

- There are still more challenges that the team will have to face before MIRI can start its scientific mission. Now that the instrument is at operating temperature, team members will take test images of stars and other known objects that can be used for calibration and to check the instrument's operations and functionality. The team will conduct these preparations alongside calibration of the other three instruments, delivering Webb's first science images this summer.

- "I am immensely proud to be part of this group of highly motivated, enthusiastic scientists and engineers drawn from across Europe and the U.S.," said Alistair Glasse, MIRI instrument scientist at the UK Astronomy Technology Centre (ATC) in Edinburgh, Scotland. "This period is our ‘trial by fire' but it is already clear to me that the personal bonds and mutual respect that we have built up over the past years is what will get us through the next few months to deliver a fantastic instrument to the worldwide astronomy community."

- MIRI was developed through a 50-50 partnership between NASA and ESA. JPL leads the U.S. efforts for MIRI, and a multinational consortium of European astronomical institutes contributes for ESA. George Rieke with the University of Arizona is the MIRI science team lead. Gillian Wright is the MIRI European principal investigator.

- Laszlo Tamas with UK ATC manages the European Consortium. The MIRI cryocooler development was led and managed by JPL, in collaboration with Northrop Grumman in Redondo Beach, California, and NASA's Goddard Space Flight Center in Greenbelt, Maryland.

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Figure 22: In this illustration, the multilayered sunshield on NASA's James Webb Space Telescope stretches out beneath the observatory's honeycomb mirror. The sunshield is the first step in cooling down Webb's infrared instruments, but the Mid-Infrared Instrument (MIRI) requires additional help to reach its operating temperature (image credits: NASA GSFC/CIL/Adriana Manrique Gutierrez)

• April 11, 2022: The James Webb Space Telescope will explore the infrared Universe. It will use four cutting-edge instruments, including the Mid-InfraRed Instrument. MIRI is one of Europe's contributions to the James Webb Space Telescope. 41)

- MIRI supports all of Webb's science goals. It will image the Universe, study planets around our own and other stars and investigate stars and galaxies across cosmic history.

 

Figure 23: The instrument will be kept extra cold by its very own 'cryocooler'. This stops heat from Webb disrupting MIRI's detectors, so the sensitive instrument can see mid-infrared light (video credit: ESA)

• April 1, 2022: The sixth stage of aligning NASA's James Webb Space Telescope's mirrors to its scientific instruments so they will create the most accurate and focused images possible has concluded. While the Mid-Infrared Instrument (MIRI) continues its cooldown, optics teams have successfully aligned the rest of the observatory's onboard instruments to Webb's mirrors. Previous alignment efforts were so accurate that the team concluded no additional adjustments to the secondary mirror are necessary until the seventh and final stage, which will involve MIRI when it has fully cooled. 42)

- "As a general rule, the commissioning process starts with coarse corrections and then moves into fine corrections. The early secondary mirror coarse corrections, however, were so successful that the fine corrections in the first iteration of Phase Six were unnecessary," said Chanda Walker, Webb wavefront sensing and control scientist, Ball Aerospace. "This accomplishment was due to many years of planning and great teamwork among the wavefront sensing team."

- Throughout the majority of the alignment process, Webb's 18 hexagonal mirrors and secondary mirror were focused into alignment to the Near-Infrared Camera (NIRCam) instrument only. Upon completing this most recent step, the observatory is now aligned to the Fine Guidance Sensor (FGS), the Near-Infrared Slitless Spectrograph (NIRISS), and the Near-Infrared Spectrometer (NIRSpec) as well as NIRCam.

- Once MIRI fully cools to its cryogenic operating temperature in the weeks ahead, a second multi-instrument alignment will occur to make final adjustments to the instruments and mirrors if needed. When the telescope is fully aligned and able to deliver focused light to each instrument, a key decision meeting will occur to confirm the end of aligning the James Webb Space Telescope. The team will then transition from alignment efforts to commissioning each instrument for scientific operations, which are expected to begin this summer.

• March 16, 2022: Following the completion of critical mirror alignment steps, NASA's James Webb Space Telescope team expects that Webb's optical performance will be able to meet or exceed the science goals the observatory was built to achieve. 43)

- On March 11, the Webb team completed the stage of alignment known as "fine phasing." At this key stage in the commissioning of Webb's Optical Telescope Element, every optical parameter that has been checked and tested is performing at, or above, expectations. The team also found no critical issues and no measurable contamination or blockages to Webb's optical path. The observatory is able to successfully gather light from distant objects and deliver it to its instruments without issue.

- Although there are months to go before Webb ultimately delivers its new view of the cosmos, achieving this milestone means the team is confident that Webb's first-of-its-kind optical system is working as well as possible.

- "More than 20 years ago, the Webb team set out to build the most powerful telescope that anyone has ever put in space and came up with an audacious optical design to meet demanding science goals," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in Washington. "Today we can say that design is going to deliver."

- While some of the largest ground-based telescopes on Earth use segmented primary mirrors, Webb is the first telescope in space to use such a design. The 21-foot, 4-inch (6.5-meter) primary mirror – much too big to fit inside a rocket fairing – is made up of 18 hexagonal, beryllium mirror segments. It had to be folded up for launch and then unfolded in space before each mirror was adjusted – to within nanometers – to form a single mirror surface.

- "In addition to enabling the incredible science that Webb will achieve, the teams that designed, built, tested, launched, and now operate this observatory have pioneered a new way to build space telescopes," said Lee Feinberg, Webb optical telescope element manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

 

Figure 24: NASA's Webb Reaches Alignment Milestone, Optics Working Successfully (video credits: NASA's Goddard Space Flight Center)

- With the fine phasing stage of the telescope's alignment complete, the team has now fully aligned Webb's primary imager, the Near-Infrared Camera, to the observatory's mirrors.

- "We have fully aligned and focused the telescope on a star, and the performance is beating specifications. We are excited about what this means for science," said Ritva Keski-Kuha, deputy optical telescope element manager for Webb at NASA Goddard. "We now know we have built the right telescope."

- Over the next six weeks, the team will proceed through the remaining alignment steps before final science instrument preparations. The team will further align the telescope to include the Near-Infrared Spectrograph, Mid-Infrared Instrument, and Near InfraRed Imager and Slitless Spectrograph. In this phase of the process, an algorithm will evaluate the performance of each instrument and then calculate the final corrections needed to achieve a well-aligned telescope across all science instruments. Following this, Webb's final alignment step will begin, and the team will adjust any small, residual positioning errors in the mirror segments.

- The team is on track to conclude all aspects of Optical Telescope Element alignment by early May, if not sooner, before moving on to approximately two months of science instrument preparations. Webb's first full-resolution imagery and science data will be released in the summer.

- Webb is the world's premier space science observatory and once fully operational, will help 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 at ESA (European Space Agency) and the Canadian Space Agency.

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Figure 25: While the purpose of this image was to focus on the bright star at the center for alignment evaluation, Webb's optics and NIRCam are so sensitive that the galaxies and stars seen in the background show up. At this stage of Webb's mirror alignment, known as "fine phasing," each of the primary mirror segments have been adjusted to produce one unified image of the same star using only the NIRCam instrument. This image of the star, which is called 2MASS J17554042+6551277, uses a red filter to optimize visual contrast (image credits: NASA/STScI)

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Figure 26: This new "selfie" was created using a specialized pupil imaging lens inside of the NIRCam instrument that was designed to take images of the primary mirror segments instead of images of the sky. This configuration is not used during scientific operations and is used strictly for engineering and alignment purposes. In this image, all of Webb's 18 primary mirror segments are shown collecting light from the same star in unison (image credits: NASA/STScI)

• March 11, 2022: Spectroscopy is an instrument application that astronomers use to better understand the physics of objects in space. 44)

- The spectrographs on board the James Webb Space Telescope (Webb) provide scientists with the data needed to analyse the materials that make up stars, nebulae, galaxies and the atmospheres of planets.

- Light that enters the telescope is split into its different wavelengths by a grating or a prism, forming a spectrum. This spectrum is then focused onto a detector. Light from each chemical element has a unique spectrum, like a fingerprint. The spectrum's pattern is analysed by astronomers to decipher which atoms and molecules are present in the source of light, and understand the physical and chemical characteristics of the source.

 

Figure 27: Instruments like NIRSpec and MIRI make spectroscopic observations of extended and complex targets (such as galaxies, nebulae, or crowded fields of stars or galaxies) in one single shot (video credit: ESA/ATG medialab)

- Webb is an international partnership between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).

• March 3, 2022: This week, the Webb team has been working on the fourth stage of mirror alignment, called Coarse Phasing, which measures and corrects smaller height differences between the mirror segments. 45)

- In the meantime this past week, Webb's Near-Infrared Spectrograph (NIRSpec) team successfully finished the check-out and initial characterization of three crucial onboard mechanisms. Today, members of the team join us to share more about the inner workings of this instrument, which was contributed by ESA (European Space Agency):

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Figure 28: This NIRSpec diagram shows the placement of the Filter Wheel Assembly (FWA), a Grating Wheel Assembly (GWA), and a Refocus Mechanism Assembly (RMA), image credit: STScI

- "To work properly as a spectrograph, NIRSpec has three mechanisms: a Filter Wheel Assembly (FWA), a Grating Wheel Assembly (GWA), and a Refocus Mechanism Assembly (RMA). The gratings in the GWA spread the incoming light over its colors or wavelengths to make a spectrum. The filters in the FWA block the wavelengths that are outside the range of interest to prevent contamination between different optical paths, or ‘orders.' The RMA adjusts the instrument focus.

- "We operated the Filter Wheel Assembly first, cycling it through all eight of its positions in both forward and reverse directions. Those eight filter wheel positions include five long-pass order-separation filters, two finite-band target acquisition filters, and an ‘opaque' position that serves as the instrument shutter. At each position, we recorded a set of reference data. This data showed us how well the wheel was moving and how accurately it settled into each position. Between each FWA position, we downloaded ‘high-capacity buffer' data from the positioning sensors, and the NIRSpec team analyzed the data. The data showed that the wheel moved very well even in the first attempt.

- "We then used a very similar procedure for the Grating Wheel Assembly, which also performed excellently the first time. The GWA is shaped like a miniature Ferris wheel and holds eight optical elements, consisting of six diffraction gratings, one prism, and a mirror. These dispersers separate the incoming light by wavelength, generating spectra that are detected by NIRSpec's sensor chips.

- "The Refocus Mechanism Assembly includes a linear translation stage that holds two flat mirrors. It will be used to fine-tune the instrument focus, compensating for any change in the overall focus position of the Webb telescope that may occur throughout the observatory's lifetime. After various initial retrievals of the RMA telemetry acquisition chain, the mechanism was moved forward a few hundred steps from launch position. Just like with the FWA and GWA, we used high-capacity buffer readouts to collect reference datasets. After the initial move, we commanded the RMA mirrors to their previous best focus position; successful completions of this test showed us that the RMA is a well-behaved and healthy mechanism.

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Figure 29: The NIRSpec thermal team from Airbus Germany of Taufkirchen and Immenstaad at the Space Telescope Science Institute in Baltimore. – Maurice Te Plate, Webb NIRSpec systems engineer, European Space Agency; Tim Rawle, Webb NIRSpec instrument scientist, European Space Agency; and Ralf Ehrenwinkler, project manager, NIRSpec post-delivery support, Airbus Defence and Space (image credit: STScI, and Jonathan Gardner, Webb deputy senior project scientist, NASA/GSFC, and Alexandra Lockwood, project scientist for Webb science communications, STScI)

• February 25, 2022: Webb continues on its path to becoming a focused observatory. The team has successfully worked through the second and third out of seven total phases of mirror alignment. With the completion of these phases, called Segment Alignment and Image Stacking, the team will now begin making smaller adjustments to the positions of Webb's mirrors. 46)

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Figure 30: This hexagonal image array captured by the NIRCam instrument shows the progress made during the Segment Alignment phase, further aligning Webb's 18 primary mirror segments and secondary mirror using precise movements commanded from the ground (image credit: NASA/STScI)

- After moving what were 18 scattered dots of starlight into Webb's signature hexagonal formation, the team refined each mirror segment's image by making minor adjustments, while also changing the alignment of Webb's secondary mirror. The completion of this process, known as Segment Alignment, was a key step prior to overlapping the light from all the mirrors so that they can work in unison.

Figure 31: This gif shows the "before" and "after" images from Segment Alignment, when the team corrected large positioning errors of its primary mirror segments and updated the alignment of the secondary mirror (image credit: NASA/STScI)

- Once Segment Alignment was achieved, the focused dots reflected by each mirror were then stacked on top of each other, delivering photons of light from each segment to the same location on NIRCam's sensor. During this process, called Image Stacking, the team activated sets of six mirrors at a time and commanded them to repoint their light to overlap, until all dots of starlight overlapped with each other.

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Figure 32: During this phase of alignment known as Image Stacking, individual segment images are moved so they fall precisely at the center of the field to produce one unified image instead of 18. In this image, all 18 segments are on top of each other. After future alignment steps, the image will be even sharper (image credit: NASA/STScI)

- "We still have work to do, but we are increasingly pleased with the results we're seeing," said Lee Feinberg, optical telescope element manager for Webb at NASA's Goddard Space Flight Center. "Years of planning and testing are paying dividends, and the team could not be more excited to see what the next few weeks and months bring."

- Although Image Stacking put all the light from a star in one place on NIRCam's detector, the mirror segments are still acting as 18 small telescopes rather than one big one. The segments now need to be lined up to each other with an accuracy smaller than the wavelength of the light.

- The team is now starting the fourth phase of mirror alignment, known as Coarse Phasing, where NIRCam is used to capture light spectra from 20 separate pairings of mirror segments. This helps the team identify and correct vertical displacement between the mirror segments, or small differences in their heights. This will make the single dot of starlight progressively sharper and more focused in the coming weeks.

• February 11, 2022: The James Webb Space Telescope is nearing completion of the first phase of the months-long process of aligning the observatory's primary mirror using the Near Infrared Camera (NIRCam) instrument. 47) 48)

- The team's challenge was twofold: confirm that NIRCam was ready to collect light from celestial objects, and then identify starlight from the same star in each of the 18 primary mirror segments. The result is an image mosaic of 18 randomly organized dots of starlight, the product of Webb's unaligned mirror segments all reflecting light from the same star back at Webb's secondary mirror and into NIRCam's detectors.

- "The entire Webb team is ecstatic at how well the first steps of taking images and aligning the telescope are proceeding. We were so happy to see that light makes its way into NIRCam," said Marcia Rieke, principal investigator for the NIRCam instrument and regents professor of astronomy, University of Arizona, USA.

- During the image capturing process that began on 2 February, Webb was repointed to 156 different positions around the predicted location of the star and generated 1560 images using NIRCam's 10 detectors, amounting to 54 gigabytes of raw data. The entire process lasted nearly 25 hours, but notedly the observatory was able to locate the target star in each of its mirror segments within the first six hours and 16 exposures. These images were then stitched together to produce a single, large mosaic that captures the signature of each primary mirror segment in one frame. The images shown here are only a center portion of that larger mosaic, a huge image with over 2 billion pixels.

- "This initial search covered an area about the size of the full Moon because the segment dots could potentially have been that spread out on the sky," said Marshall Perrin, deputy telescope scientist for Webb and astronomer at the Space Telescope Science Institute in Baltimore, USA. "Taking so much data right on the first day required all of Webb's science operations and data processing systems here on Earth working smoothly with the observatory in space right from the start. And we found light from all 18 segments very near the center early in that search! This is a great starting point for mirror alignment."

- Each unique dot visible in the image mosaic is the same star as imaged by each of Webb's 18 primary mirror segments, a treasure trove of detail that optics experts and engineers will use to align the entire telescope. This activity determined the post-deployment alignment positions of every mirror segment, which is the critical first step in bringing the entire observatory into a functional alignment for scientific operations.

- NIRCam is the observatory's wavefront sensor and a key imager. It was intentionally selected to be used for Webb's initial alignment steps because it has a wide field of view and the unique capability to safely operate at higher temperatures than the other instruments. It is also packed with customized components that were designed to specifically aid in the process. NIRCam will be used throughout nearly the entire alignment of the telescope's mirrors. It is, however, important to note that NIRCam is operating far above its ideal temperature while capturing these initial engineering images, and visual artifacts can be seen in the mosaic. The impact of these artifacts will lessen significantly as Webb draws closer to its ideal cryogenic operating temperatures.

- "Launching Webb to space was of course an exciting event, but for scientists and optical engineers, this is a pinnacle moment, when light from a star is successfully making its way through the system down onto a detector," said Michael McElwain, Webb observatory project scientist, NASA's Goddard Space Flight Center.

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Figure 33: Webb sees its first star - 18 times. What looks like a simple image of blurry starlight now becomes the foundation to align and focus the telescope in order for Webb to deliver unprecedented views of the universe this summer. Over the next month or so, the team will gradually adjust the mirror segments until the 18 images become a single star (image credit: NASA)

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Figure 34: Webb sees its first star - annotated. This image mosaic was created by pointing the James Webb Space Telescope at a bright, isolated star in the constellation Ursa Major known as HD 84406. This star was chosen specifically because it is easily identifiable and not crowded by other stars of similar brightness, which helps to reduce background confusion. Each dot within the mosaic is labeled by the corresponding primary mirror segment that captured it. These initial results closely match expectations and simulations (image credit: NASA)

- Moving forward, Webb's images will only become clearer, more detail-laden, and more intricate as its other three instruments arrive at their intended cryogenic operating temperatures and begin capturing data. The first scientific images are expected to be delivered to the world in the summer. Though this is a big moment, confirming that Webb is a functional telescope, there is much ahead to be done in the coming months to prepare the observatory for full scientific operations using all four of its instruments.

• January 31, 2022: Following Webb's arrival at its orbital destination around Lagrange Point 2 (L2) on Jan. 24, the mission operations team began working its way through a critical series of steps: powering on all the science instruments, turning off heaters to begin a long cooldown process, and ultimately capturing the first photons on Webb's primary camera to enable a months-long alignment of the telescope. 49)

- While the MIRI instrument and some instrument components were powered on in the weeks after Webb's Dec. 25 launch, the team didn't finish turning on the remaining three instruments – NIRCam, NIRSpec, and FGS/NIRISS – until the past few days.

- The mission operations team's next major step is to turn off instrument heaters. The heaters were necessary to keep critical optics warm to prevent the risk of water and ice condensation. As the instruments meet pre-defined criteria for overall temperatures, the team is shutting off these heaters to allow the instruments to restart the months-long process of cooling to final temperatures.

- When NIRCam reaches 120 kelvins (approximately -244 degrees Fahrenheit, or -153 degrees Celsius), Webb's optics team will be ready to begin meticulously moving the 18 primary mirror segments to form a single mirror surface. The team has selected the star HD 84406 as its target to begin this process. It will be the first object NIRCam "sees" when photons of light hit the instrument's powered-on detectors. The process will essentially create an image of 18 random, blurry points of light. For the first few weeks of mirror alignment, the team will keep the instrument trained on the star while they make microscopic adjustments to the mirror segments; ultimately that collection of 18 blurry dots will become a focused image of a single star. Cooling of the telescope and instruments will also continue over the next month, with the near-infrared instruments ultimately reaching 37-39 kelvins. The cryocooler will cool MIRI to 6 kelvins in the following months.

• January 24, 2022: Today, at 2 p.m. EST, Webb fired its onboard thrusters for nearly five minutes (297 seconds) to complete the final postlaunch course correction to Webb's trajectory. This mid-course correction burn inserted Webb toward its final orbit around the second Sun-Earth Lagrange point, or L2, nearly 1 million miles away from the Earth. 50)

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Figure 35: The final mid-course burn added only about 3.6 miles per hour (1.6 m/s) – a mere walking pace – to Webb's speed, which was all that was needed to send it to its preferred "halo" orbit around the L2 point (image credit: Steve Sabia/NASA Goddard)

- "Webb, welcome home!" said NASA Administrator Bill Nelson. "Congratulations to the team for all of their hard work ensuring Webb's safe arrival at L2 today. We're one step closer to uncovering the mysteries of the universe. And I can't wait to see Webb's first new views of the universe this summer!"

- Webb's orbit will allow it a wide view of the cosmos at any given moment, as well as the opportunity for its telescope optics and scientific instruments to get cold enough to function and perform optimal science. Webb has used as little propellant as possible for course corrections while it travels out to the realm of L2, to leave as much remaining propellant as possible for Webb's ordinary operations over its lifetime: station-keeping (small adjustments to keep Webb in its desired orbit) and momentum unloading (to counteract the effects of solar radiation pressure on the huge sunshield).

- "During the past month, JWST has achieved amazing success and is a tribute to all the folks who spent many years and even decades to ensure mission success," said Bill Ochs, Webb project manager at NASA's Goddard Space Flight Center. "We are now on the verge of aligning the mirrors, instrument activation and commissioning, and the start of wondrous and astonishing discoveries."

- Now that Webb's primary mirror segments and secondary mirror have been deployed from their launch positions, engineers will begin the sophisticated three-month process of aligning the telescope's optics to nearly nanometer precision.

• January 12. 2022: Webb has begun the detailed process of fine-tuning its individual optics into one huge, precise telescope. 51)

- Engineers first commanded actuators – 126 devices that will move and shape the primary mirror segments, and six devices that will position the secondary mirror – to verify that all are working as expected after launch. The team also commanded actuators that guide Webb's fine steering mirror to make minor movements, confirming they are working as expected. The fine steering mirror is critical to the process of image stabilization.

- Ground teams have now begun instructing the primary mirror segments and secondary mirror to move from their stowed-for-launch configuration, off of snubbers that kept them snug and safe from rattling from vibration. These movements will take at least ten days, after which engineers can begin the three-month process of aligning the segments to perform as a single mirror.

• January 8, 2022: NASA's James Webb Space Telescope team fully deployed its 21-foot (6.4 m), gold-coated primary mirror, successfully completing the final stage of all major spacecraft deployments to prepare for science operations. 52)

- A joint effort with the European Space Agency (ESA) and Canadian Space Agency, the Webb mission will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe.

- "Today, NASA achieved another engineering milestone decades in the making. While the journey is not complete, I join the Webb team in breathing a little easier and imagining the future breakthroughs bound to inspire the world," said NASA Administrator Bill Nelson. "The James Webb Space Telescope is an unprecedented mission that is on the precipice of seeing the light from the first galaxies and discovering the mysteries of our universe. Each feat already achieved and future accomplishment is a testament to the thousands of innovators who poured their life's passion into this mission."

- The two wings of Webb's primary mirror had been folded to fit inside the nose cone of an Arianespace Ariane 5 rocket prior to launch. After more than a week of other critical spacecraft deployments, the Webb team began remotely unfolding the hexagonal segments of the primary mirror, the largest ever launched into space. This was a multi-day process, with the first side deployed Jan. 7 and the second Jan. 8.

- Mission Operations Center ground control at the Space Telescope Science Institute in Baltimore began deploying the second side panel of the mirror at 8:53 a.m. EST. Once it extended and latched into position at 1:17 p.m. EST, the team declared all major deployments successfully completed.

- The world's largest and most complex space science telescope will now begin moving its 18 primary mirror segments to align the telescope optics. The ground team will command 126 actuators on the backsides of the segments to flex each mirror – an alignment that will take months to complete. Then the team will calibrate the science instruments prior to delivering Webb's first images this summer.

- "I am so proud of the team – spanning continents and decades – that delivered this first-of-its kind achievement," said Thomas Zurbuchen, associate administrator for the Science Mission Directorate in NASA Headquarters in Washington. "Webb's successful deployment exemplifies the best of what NASA has to offer: the willingness to attempt bold and challenging things in the name of discoveries still unknown."

- Soon, Webb will also undergo a third mid-course correction burn – one of three planned to place the telescope precisely in orbit around the second Lagrange point, commonly known as L2, nearly 1 million miles from Earth. This is Webb's final orbital position, where its sunshield will protect it from light from the Sun, Earth, and Moon that could interfere with observations of infrared light. Webb is designed to peer back over 13.5 billion years to capture infrared light from celestial objects, with much higher resolution than ever before, and to study our own solar system as well as distant worlds.

- "The successful completion of all of the Webb Space Telescope's deployments is historic," said Gregory L. Robinson, Webb program director at NASA Headquarters. "This is the first time a NASA-led mission has ever attempted to complete a complex sequence to unfold an observatory in space – a remarkable feat for our team, NASA, and the world."

- NASA's Science Mission Directorate oversees the mission. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the project for the agency and oversees the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including Johnson Space Center in Houston, the Jet Propulsion Laboratory in Pasadena, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in Silicon Valley, and others.

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Figure 36: This artist's conception of the James Webb Space Telescope in space shows all its major elements fully deployed. The telescope was folded to fit into its launch vehicle, and then was slowly unfolded over the course of two weeks after launch (image credits: NASA GSFC/CIL/Adriana Manrique Gutierrez)

• January 5, 2022: While the Webb team was tensioning the sunshield, other activities were also taking place among the instruments. One milestone: unlocking the Mid-Infrared Instrument (MIRI) Contamination Control Cover. We've asked Gillian Wright, European principal investigator for MIRI, to tell us about it. 53)

- "MIRI has a Contamination Control Cover, because the constraints of its extra-cold operating temperature mean that it is not possible to include other means of dealing with ice contamination, such as heaters for sensitive components. For launch it was safest to have this cover locked, and the timing for operating it is driven by the temperatures of the observatory.

- "To unlock the cover, we first had to power on our Instrument Control Electronics and confirm that they were functioning correctly. Then the commands to the cover could be sent. After successfully completing the tests and unlocking the cover, the instrument control electronics were then powered off before the next steps on the sunshield tensioning activities. This key step for MIRI was monitored remotely by team members in Europe, ready to provide assistance if it were needed.

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Figure 37: "The picture here shows tired and happy MIRI team members at the Mission Operations Center in Baltimore, after completing this first of the many MIRI commissioning steps. The MIRI Contamination Control Cover will be closed in the next few days to protect the optics from any possible contaminants as the observatory cools. It will then be reopened much later in the timeline, when MIRI has cooled to its operating temperature of just 7K and is ready to look out at the sky."(Gillian Wright, European principal investigator for the Mid-Infrared Instrument, UK Astronomy Technology Centre)

• January 5, 2022: Today, Webb teams successfully deployed the observatory's secondary mirror support structure. When light from the distant universe hits Webb's iconic 18 gold primary mirrors, it will reflect off and hit the smaller, 2.4-foot (0.74 m) secondary mirror, which will direct the light into its instruments. The secondary mirror is supported by three lightweight deployable struts that are each almost 25 feet long and are designed to withstand the space environment. Specialized heating systems were used to warm up the joints and motors needed for seamless operation. 54)

- "Another banner day for JWST," said Bill Ochs, Webb project manager at NASA's Goddard Space Flight Center, as he congratulated the secondary mirror deployment team at the Mission Operations Center in Baltimore. "This is unbelievable…We're about 600,000 miles from Earth, and we actually have a telescope."

- The deployment process began at approximately 9:52 a.m. EST, and the secondary mirror finished moving into its extended position at about 11:28 a.m. EST. The secondary mirror support structure was then latched at about 11:51 a.m. EST. At approximately 12:23 p.m. EST, engineers confirmed that the structure was fully secured and locked into place and the deployment was complete.

- "The world's most sophisticated tripod has deployed," said Lee Feinberg, optical telescope element manager for Webb at Goddard. "That's really the way one can think of it. Webb's secondary mirror had to deploy in microgravity, and in extremely cold temperatures, and it ultimately had to work the first time without error. It also had to deploy, position, and lock itself into place to a tolerance of about one and a half millimeters, and then it has to stay extremely stable while the telescope points to different places in the sky – and that's all for a secondary mirror support structure that is over 7 meters in length."

- Next Webb will deploy an important radiator system known as the aft deployable instrument radiator (ADIR), which helps shed heat away from its instruments and mirrors.

• January 4, 2022: The James Webb Space Telescope team has fully deployed the spacecraft's 70-foot sunshield, a key milestone in preparing it for science operations. 55) 56)

- The sunshield – about the size of a tennis court at full size – was folded to fit inside the payload area of an Arianespace Ariane 5 rocket's nose cone prior to launch. The Webb team began remotely deploying the sunshield Dec. 28, 2021, three days after launch.

- "This is the first time anyone has ever attempted to put a telescope this large into space," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at the agency's headquarters in Washington. "Webb required not only careful assembly but also careful deployments. The success of its most challenging deployment – the sunshield – is an incredible testament to the human ingenuity and engineering skill that will enable Webb to accomplish its science goals."

- The five-layered sunshield will protect the telescope from the light and heat of the Sun, Earth, and Moon. Each plastic sheet is about as thin as a human hair and coated with reflective metal, providing protection on the order of more than SPF 1 million. Together, the five layers reduce exposure from the Sun from over 200 kW of solar energy to a fraction of a watt.

- This protection is crucial to keep Webb's scientific instruments at temperatures of 40 kelvins, or under minus 380 degrees Fahrenheit – cold enough to see the faint infrared light that Webb seeks to observe.

- "Unfolding Webb's sunshield in space is an incredible milestone, crucial to the success of the mission," said Gregory L. Robinson, Webb's program director at NASA Headquarters. "Thousands of parts had to work with precision for this marvel of engineering to fully unfurl. The team has accomplished an audacious feat with the complexity of this deployment – one of the boldest undertakings yet for Webb."

- The unfolding occurred in the following order, over the course of eight days:

a) Two pallet structures – forward and aft – unfolded to bring the observatory to its full 70-foot length

b) The Deployable Tower Assembly deployed to separate the telescope and instruments from the sunshield and the main body of the spacecraft, allowing room for the sunshield to fully deploy

c) The aft momentum flap and membrane covers were released and deployed

d) The mid-booms deployed, expanding perpendicular to the pallet structures and allowing the sunshield to extend to its full width of 47 feet

e) Finally, at approximately 11:59 a.m. EST Tuesday (Jan. 4), the sunshield was fully tensioned and secured into position, marking the completion of the sunshield deployment.

- The unfolding and tensioning of the sunshield involved 139 of Webb's 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys, and 90 individual cables totaling roughly one quarter of a mile in length. The team also paused deployment operations for a day to work on optimizing Webb's power systems and tensioning motors, to ensure Webb was in prime condition before beginning the major work of sunshield tensioning.

- "The sunshield is remarkable as it will protect the telescope on this historic mission," said Jim Flynn, sunshield manager at Northrop Grumman, NASA's primary contractor for Webb. "This milestone represents the pioneering spirit of thousands of engineers, scientists, and technicians who spent significant portions of their careers developing, designing, manufacturing, and testing this first-of-its-kind space technology."

- The world's largest and most complex space science observatory has another 5 1/2 months of setup still to come, including deployment of the secondary mirror and primary mirror wings, alignment of the telescope optics, and calibration of the science instruments. After that, Webb will deliver its first images.

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Figure 38: On Jan. 4, 2022, engineers successfully completed the deployment of the James Webb Space Telescope's sunshield, seen here during its final deployment test on Earth in December 2020 at Northrop Grumman in Redondo Beach, California. The five-layer, tennis court-sized sunshield is essential for protecting the telescope from heat, allowing Webb's instruments to cool down to the extremely low temperatures necessary to carry out its science goals (image credits: NASA/Chris Gunn)

- The telescope's revolutionary technology will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, to everything in between. Webb will reveal new and unexpected discoveries and help humanity understand the origins of the universe and our place in it.

- The James Webb Space Telescope is an international partnership with the ESA (European Space Agency) and the Canadian Space Agency. NASA Headquarters oversees the mission. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency's Johnson Space Center in Houston, Jet Propulsion Laboratory in Southern California, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in California's Silicon Valley, and others.

• January 4, 2022: Spacecraft controllers started the final steps in the deployment of the sunshield of the James Webb Space Telescope Jan. 3 after fixing two minor issues with the spacecraft. 57)

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Figure 39: After launch, JWST requires two weeks of major deployments of its sunshield and telescope, a process with many potential failure modes (image credit: NASA GSFC/CIL/Adriana Manrique Gutierrez)

- NASA announced late Jan. 3 that it had completed the tensioning of three of the five layers of aluminum-coated Kapton that comprise the sunshield, which blocks sunlight from reaching the telescope and its instruments to cool them. That tensioning process, involving a series of motors, pulleys and cables, stretches the layers into the final shape and ensures proper separation between the layers.

- That work appeared to be going faster than expected. During a briefing with reporters around midday Jan. 3, Bill Ochs, JWST project manager at NASA's Goddard Space Flight Center, said tensioning of the outermost of the five layers had started, with plans to work inward layer by layer.

- "Today we are focused on tensioning layer 1. Layer 1 will take most of the day," he said. "Tomorrow through Wednesday we will deploy layers 2 through 5."

- With three of the five layers already deployed, though, NASA now expects to complete the final two layers, and thus the overall sunshield deployment process, Jan. 4. "This was the hardest part to test on the ground, so it feels awesome to have everything go so well today," said James Cooper, JWST sunshield manager at Goddard, in a NASA statement late Jan. 3. "The Northrop and NASA team is doing great work, and we look forward to tensioning the remaining layers."

- The tensioning was originally scheduled to start the day after the deployment of two booms on either side of the spacecraft that extended the sunshield to its full area. However, that deployment took longer than expected Dec. 31, and managers decided to give controllers the day off Jan. 1 to rest.

- Engineers then spent Jan. 2 resolving two minor issues with the spacecraft. One involved what Ochs described as a "preset max duty cycle" setting in the solar arrays that kept them from producing enough power to meet all the spacecraft needs. As a result, the spacecraft was using its battery in addition to power from the arrays.

- Amy Lo, vehicle engineering lead for JWST and prime contractor Northrop Grumman, said at the media briefing that controllers "rebalanced" the array by adjusting settings on each of its five individual panels. "We got the arrays to where they ought to be in order to provide the power that we need on Webb. We're power-positive, the arrays look good," she said.

- The other issue involved motors used for the tensioning process whose temperatures were higher than expected although still within conservative engineering margins. Controllers adjusted the orientation of the spacecraft temporarily to reduce the amount of sunlight hitting, and heating up, the motors. "They're nice and cool," Lo said of the motors. "We've got a lot of margin now on our temperature."

- Once the sunshield is fully tensioned, spacecraft controllers will turn their attention to JWST's mirrors. Ochs said the tripod holding the secondary mirror could be deployed late in the week, followed over the weekend by two wings holding segments of the primary mirror as well as an aft radiator.

- Getting the sunshield in place, though, will be a major step toward completing the full deployment of JWST. Ochs estimated that, once the sunshield is fully tensioned, the mission will have retired 70–75% of the 344 single-point failures in the spacecraft.

- "When I get asked, ‘What keeps you up the most at night?' obviously it's the sunshield deployment," he said. "I don't expect any drama. I always tell folks, the best thing for operations is boring, and that's what we anticipate over the next three days, to be boring. I think we'll all breathe a sigh of relief once we get to the final layer, layer 5, tensioning. But I don't expect drama."

• December 29, 2021: After a successful launch of NASA's James Webb Space Telescope Dec. 25, and completion of two mid-course correction maneuvers, the Webb team has analyzed its initial trajectory and determined the observatory should have enough propellant to allow support of science operations in orbit for significantly more than a 10-year science lifetime. (The minimum baseline for the mission is five years.) 58)

- The analysis shows that less propellant than originally planned for is needed to correct Webb's trajectory toward its final orbit around L2, a point of gravitational balance on the far side of Earth away from the Sun. Consequently, Webb will have much more than the baseline estimate of propellant – though many factors could ultimately affect Webb's duration of operation.

- Webb has rocket propellant onboard not only for midcourse correction and insertion into orbit around L2, but also for necessary functions during the life of the mission, including "station keeping" maneuvers – small thruster burns to adjust Webb's orbit — as well as what's known as momentum management, which maintains Webb's orientation in space.

- The extra propellant is largely due to the precision of the Arianespace Ariane 5 launch, which exceeded the requirements needed to put Webb on the right path, as well as the precision of the first mid-course correction maneuver – a relatively small, 65-minute burn after launch that added approximately 45 mph (20 m/s) to the observatory's speed. A second correction maneuver occurred on Dec. 27, adding around 6.3 mph (2.8 m/s) to the speed.

- The accuracy of the launch trajectory had another result: the timing of the solar array deployment. That deployment was executed automatically after separation from the Ariane 5 based on a stored command to deploy either when Webb reached a certain attitude toward the Sun ideal for capturing sunlight to power the observatory – or automatically at 33 minutes after launch. Because Webb was already in the correct attitude after separation from the Ariane 5 second stage, the solar array was able to deploy about a minute and a half after separation, approximately 29 minutes after launch.

- From here on, all deployments are human-controlled so deployment timing – or even their order — may change. Explore what's planned here.

• December 25, 2021: At 7:50 p.m. EST (corresponding to 00:50 UTC on Dec. 26), Webb's first mid-course correction burn began. It lasted 65 minutes and is now complete. This burn is one of two milestones that are time critical — the first was the solar array deployment, which happened shortly after launch. 59)

- This burn adjusts Webb's trajectory toward the second Lagrange point, commonly known as L2. After launch, Webb needs to make its own mid-course thrust correction maneuvers to get to its orbit. This is by design: Webb received an intentional slight under-burn from the Ariane-5 that launched it into space, because it's not possible to correct for overthrust. If Webb gets too much thrust, it can't turn around to move back toward Earth because that would directly expose its telescope optics and structure to the Sun, overheating them and aborting the science mission before it can even begin.

- Therefore, we ease up to the correct velocity in three stages, being careful never to deliver too much thrust — there will be three mid-course correction maneuvers in total.

- After this burn, no key milestones are time critical, so the order, location, timing, and duration of deployments may change.

• December 25, 2021: From one space flier to another, ESA astronaut Matthias Maurer shares a message of support for the James Webb Space Telescope (Webb) launch, from ESA's Columbus science laboratory on the International Space Station. 60)

- Matthias is currently living and working in space for his first mission known as Cosmic Kiss. He describes the mission of Webb as part of humankind's biggest adventure, as we explore the cosmos to understand our place within it.

 

Figure 40: Best wishes to the JWST mission from Matthias Maurer on the ISS (video credit: ESA)

- Webb is the next great space science observatory following Hubble, designed to answer outstanding questions about the Universe and to make breakthrough discoveries in all fields of astronomy. It is an international partnership between the European Space Agency ESA, US space agency NASA, and the Canadian Space Agency CSA, and has been launched on an Ariane 5 rocket from Europe's Spaceport in French Guiana.

- Webb is designed to see farther into our origins: from the formation of stars and planets to the birth of the first galaxies in the early Universe, just as the International Space Station enables us to learn more about our home planet.

 

Development status of the JWST project

Feature Stories of the Solar System and Beyond

 

 


 

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. 61) 62) 63) 64) 65) 66) 67) 68) 69)

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Figure 41: The three elements of the JWST flight segment (image credit: NASA) 70)

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Figure 42: The JWST spacecraft, reflecting the addition of the trim flap and the new solar panel array (image credit: NASA)

Item

Feature

Benefit

OTE
(Optical Telescope Element)

- TMA (Three Mirror Anastigmatic) design, f/20, 25 m2 collecting area
- Fine steering mirror (FSM) with line-of-sight (LOS) stabilization < 7.3 marcsec (or mas)
- Four separate deployments
- Semi-rigid hexagonal mirror segments and graphite composite backplane structure

- Superior image quality over the ISIM FOV, provides science resolution and sensitivity
- Excellent pointing control and stability in conjunction with the spacecraft attitude control
- Simple, reliable and robust deployment
- Allows ground verification of the OTE, provides stable optical performance over temperature

Primary mirror

- Primary mirror deploys in two steps (2-chord fold)
- Composed of 18 semi-rigid hexagonal segments, each with set-and-monitor wavefront control actuators
- Mirror segment material is Beryllium

- Highly reliable deployment
- All segments are mechanically near-identical, achieving efficiencies in manufacturing, assembly and testing
- Known material properties with demonstrated optical performance over temperature

Secondary mirror

- Tripod configuration for support structure
- Deployment using a single redundant actuator
- Semi-rigid optic with 6 degrees of freedom (DoF) alignment

- Provides rigidity, minimizes obscuration and scattered light into the field of view
- Low risk, high margin (torque margin > 32 times the friction load)
- Permits reliable and accurate telescope alignment

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.
- Contains all science instruments (SI) and FGS

- Provides a simple interface for the ISIM to decouple ISIM development from the OTE
- Allows for parallel development and early testing

Tower

- Integral 1 Hz passive vibration isolators
- Thermally isolates the OTE from the spacecraft

- Reduces S/C dynamic noise onto OTE/ISIM
- Achieves small mirror temperature gradients

Sunshield

- 5 layer "V" groove radiator design reduces solar energy to a few 10's of mW
- Folded about OTE during launch
- Sized (~19.4 m x 11.4 m) and shaped to limit solar radiation induced momentum buildup

- Provides a stable thermal environment for passively cooling the OTE and the ISIM
- Reliable deployment, protects OTE during launch
- Reduces the time and fuel for momentum unloading, increases operational efficiency

S/C bus

- Chandra-based attitude control subsystem
- Two-axis gimbaled high gain Earth-pointing antenna (omni-directional), Ka- and S-band
- 471 Gbit solid state recorder
- Propellant for >11 years

- Flight-proven low noise dynamic environment that minimizes line-of-sight jitter
- Contingency operations and link margin
- Store > 2 days of science & engineering data
- Extended operation capability

Table 1: 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
NIRCam
FGS tunable
NIRSpec
NIRSpec
MIRI
NIRSpec Med
MIRI Spec
MIRI Spec

- SNR=10, integration time = τi, R=λ/Δλ and Zodicial of 1.2 times that at north ecliptic pole
- 12 nJy (1.1 μm, τi=10,000 s, and λ/Δλ= 4)
- 10.4 nJy (2.0 μm, τi=10,000 s, and λ/Δλ = 4)
- 368 nJy (3.5 μm, τi=10,000 s, and λ/Δλ = 100)
- 120 nJy (3.0 μm, τi=10,000 s, and λ/Δλ = 100)
- 560 nJy (10 μm, τi=10,000 s, and λ/Δλ = 5)
- 5000 nJy (21 μm, τi=10,000 s, and λ/Δλ = 4.2)
- 5.2 x 10-22 Wm-2 (2 µm, τi=100,000 s, R=1000)
- 3.4 x 10-21 Wm-2 (9.2 µm, τi=10,000 s, R=2400)
- 3.1 x 10-20 Wm-2 (22.5 µm, τi=10,000 s, R=1200)

Celestial sphere coverage





Overall
observing efficiency

- 100% annually
- 39.7% at any given time
- 100% of sphere has at least 51 contiguous days visibility
- 30% for > 197 days
- Continuous within 5º of ecliptic poles

- Observatory ~80.7%

Spatial
resolution
& stability

- Encircled Energy of 75% at 1 µm for 150 mas radius
- Strehl ratio of ~ 0.86 at 2 µm.
- PSF stability better than 1%

Mission life

- 5-year minimum lifetime
- 11 years for fuel
- Commissioning in < 6 months

Telescope FOV

- 166 arcmin x 166 arcmin FOV
-ISIM instruments share FOV with common aperture

Launch

2019

Table 2: 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.

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Figure 43: 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: 71) 72)

• 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 44. The numbers 1 to 6 represent the six-fold symmetry of the hexagonal packing of the primary mirror.

Figure 45 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. 73)

JWST_Auto40

Figure 44: Arrangement and designation of primary mirror segments and images of the mirrors (image credit: NASA, BATC)

Legend to Figure 44: 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.

JWST_Auto3F

Figure 45: 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.

JWST_Auto3E

Figure 46: Illustration of the OTE subsystems/assemblies (image credit: NASA, STScI) 74)

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).

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Figure 47: Conceptual layout of the OTE and interfaces to ISIM (image credit: NGAS, STScI)

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Figure 48: 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. 75) 76) 77) 78) 79)

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.

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Figure 49: ISIM is the science instrument payload of JWST (image credit: NASA) 80)

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Figure 50: 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 47.

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. 81)

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.

JWST_Auto39

Figure 51: ISIM components within the Observatory (image credit: NASA)

Instrument

Spectral range (µm)

Optical elements

FPA

Plate scale
(marcsec/pixel)

FOV (Field of View)

NIRCam (Short
Wave)

0.6 - 2.3

Fixed filters
(R~4, R~10, R~100),
coronagraphic spots

Two 2 x 2 mosaics of 2048 x 2048 arrays

32

2.2' x 4.4'
(arcmin)

NIRCam (Long
Wave)

2.4 - 5.0

Fixed filters
(R~4, R~10, R~100),
coronagraphic spots

Two
2048 x 2048
arrays

65

2.2' x 4.4'

NIRSpec (prism,
R=100 resolving power)

0.6 - 5.0

Transmissive slit mask:
4 x 384 x 175 micro-shutter
array, 250 (spectral) by 500
(spatial) marcsec; fixed
slits 200 or 300 marcsec wide
by 10 cm long

Two
2048 x 2048
arrays

100

3.4' x 3.1'

NIRSpec (Grating,
R=1000)

1.0 - 5.0

NIRSpec (IFU,
R=3000)

1.0 - 5.0

IFU (Integrated Field Unit)

3.0" x 3.0"
(arcsec)

MIRI (Imaging)

5 - 28

Broad-band filters,
coronagraphic spots &
phase masks

1024 x 1024

110

1.4' x 1.9'
(26" x 26"
coronagraphic)

MIRI (Prism
spectroscopy)

5 -10

R ~ 100

MIRI
(Spectroscopy)

5 - 28

Integral field spectrograph
(R~3000) in 4 bands

Two 1024 x 1024
arrays

200-470 depending on band

3.6" x 3.6" to
7.5" x 7.5"

FGS

1.5 – 2.6
3.1 – 4.8

Order-blocking
filters+etalon (R~100)

2048 x 2048

68

2.3' x 2.3'

Table 3: 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 54. The cold portion of the ISIM is integrated with the OTE.

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Figure 52: Schematic diagram of the accommodation of the four science instruments in ISIM (image credit: NASA)

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Figure 53: NASA engineers check out the unwrapped ISIM structure in a clean room in 2009 (image credit: NASA) 82)

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Figure 54: ISIM focal plane allocation layout (image credit: STScI, NASA)

Legend to Figure 54: 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.

JWST_Auto35

Figure 55: 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 55: 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. 83)

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: 84)

- 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.

JWST_Auto34

Figure 56: The ISIM structure and flight instruments, re-integrated and ready for environmental testing (image credit: NASA, Chris Nunn)

 

Note: As of the launch of the JWST spacecraft on December 25 2021, the JWST file has been split into additional files, to make the file handling manageable for all parties concerned, in particular for the user community.

 

 


 

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: 85) 86) 87) 88) 89) 90)

• 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
R=100 imaging: Two 2.16 x 2.16 arcmin fields (one λ<2.5µm, one λ>2.5µm)

Spatial resolution

Imaging: 0.0317 arcsec/pixel, λ<2.5µm; 0.068 arcsec/pixel, λ > 2.5µm
R=100: 0.0648 arcsec/pixel

Coronagraphy

Choice of coronagraphic spots and pupils in all instrument sections

Table 4: 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
2.4 to 5

0.6 to 2.3
2.4 to 5

1.2 to 2.5
1 to 2.5 goal

2.5 to 4.5
2.3 to 5 goal

Nyquist sampling (µm)

2 / 4

2 / 4

4

4

Pixel format

4096 x 4096 (short λ)
2048 x 2048 (long λ)

4096 x 4096 (short λ)
2048 x 2048 (long 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 5: NIRCam module characteristics