NASA’s 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, or MIRI.
The MIRI test image (at 7.7 microns) 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 microns). The retired Spitzer telescope was one of NASA’s Great Observatories and the first to provide high-resolution images of the near- and mid-infrared universe. Webb, with its significantly larger primary mirror and improved detectors, will allow us to see the infrared sky with improved clarity, enabling even more discoveries.
For example, Webb’s MIRI image shows the interstellar gas in unprecedented detail. Here, you can see the emission from “polycyclic aromatic hydrocarbons,” or 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.
Credit: NASA/ESA/CSA/STScI
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 11 a.m., 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.
On May 1, the nonprofit, nonpartisan Partnership for Public Service announced the 2022 finalists for the Samuel J. Heyman Service to America Medal (Sammies) – an awards program honoring excellence and innovation in federal service. Among the finalists is Gregory L. Robinson, program director for the James Webb Space Telescope at NASA Headquarters.
Selected from more than 400 nominations, Robinson has been named a Management Excellence finalist for his achievements in overseeing NASA’s largest and most complex international space science program, which will enable scientific breakthroughs in nearly every branch of astronomy.
“Greg Robinson is a leader who epitomizes excellence,” said Thomas Zurbuchen, NASA’s associate administrator for the Science Mission Directorate. “Across a massive international program of diverse teams and perspectives, he built the trust, consensus, and motivation to see this revolutionary mission to launch.”
Webb launched on Dec. 25, 2021, and endured a harrowing multi-week spacecraft commissioning period where hundreds of intricate parts synchronized to work successfully in the harsh environment of space while on its journey to its final orbit one million miles from Earth.
“I am very honored to be considered for a Service to America Medal,” Robinson said. “Working with an incredible, resilient team and partners across the globe to overcome many challenges has been a great privilege. I have enjoyed a great career at NASA for over 30 years, and to be a part of the mission’s historic moment when Webb launched flawlessly on Christmas Day was an awe-inspiring gift.”
Since its inception in 2002, the Sammies have honored more than 650 outstanding federal employees. Robinson is among 30 federal employees across 22 federal agencies honored as 2022 Sammies finalists for their outstanding contributions to safety, public health, and sustainability across our nation and the world.
Prior to leading Webb, Robinson served as the deputy associate administrator for programs in NASA’s Science Mission Directorate. He is a veteran executive, who previously served as deputy center director at NASA’s Glenn Research Center in Cleveland, NASA deputy chief engineer, and as the acting National Environmental Satellite, Data, and Information Service deputy assistant administrator at the National Oceanic and Atmospheric Administration.
Greg Robinson, program director for NASA’s James Webb Space Telescope Program at NASA Headquarters, gives a brief interview on NASA Television as he and the launch team monitor the countdown to Webb’s launch Dec. 25, 2021, at Europe’s Spaceport in Kourou, French Guiana. Webb is a large infrared telescope with a 21.3-foot (6.5-meter) primary mirror. The observatory will study every phase of cosmic history—from within our solar system to the most distant observable galaxies in the early universe. Credit: NASA/Bill Ingalls
Webb is the first space science telescope to use a large primary mirror that consists of 18 segments and an unparalleled optical system that recently showed the world its first focused image of a single star. Recently, the Webb team successfully aligned the telescope, confirming it can capture focused images with its four onboard science instruments. Now, it is undergoing the process of commissioning the instruments so it can deliver spectacular images and spectra this summer.
The observatory will enable the study of every phase of 13.5 billion years of cosmic history – from within our solar system to the most distant observable galaxies in the early universe – to everything in between.
More About the Sammies
More information about the program and the 2022 finalists is available online. All finalists are eligible for the Service to America Medals People’s Choice Award. Beginning Monday, May 2, members of the public may vote online for the federal employee they believe has made the most significant contribution to the American people. The People’s Choice winner will be announced in the summer.
More About the Webb Mission
The James Webb Space Telescope, the largest and most complex science observatory ever built, is an international program led by NASA with its partners, the European Space Agency and the Canadian Space Agency. As the scientific successor to the Hubble Space Telescope, Webb will explore the secrets of the universe and reveal new discoveries to help us understand our place in the cosmos.
After meeting the major milestone of aligning the telescope to NIRCam, the Webb team is starting to extend the telescope alignment to the guider (the Fine Guidance Sensor, or FGS) and the other three science instruments. This six-week-long process is called multi-instrument multi-field (MIMF) alignment.
When a ground-based telescope switches between cameras, sometimes the instrument is physically taken off the telescope, and a new one is installed during the daytime when the telescope is not in use. If the other instrument is already on the telescope, mechanisms are in place to move part of the telescope’s optics (known as a pick-off mirror) into the field of view.
On space telescopes like Webb, all the cameras see the sky at the same time; to switch a target from one camera to another, we repoint the telescope to put the target into the field of view of the other instrument.
After MIMF, Webb’s telescope will provide a good focus and sharp images in all the instruments. In addition, we need to precisely know the relative positions of all the fields of view. Over last weekend, we mapped the positions of the three near-infrared instruments relative to the guider and updated their positions in the software that we use to point the telescope. In another instrument milestone, FGS recently achieved “fine guide” mode for the first time, locking onto a guide star using its highest precision level. We have also been taking “dark” images, to measure the baseline detector response when no light reaches them – an important part of the instrument calibration.
Webb’s guider (FGS) and four science instruments (NIRCam, NIRSpec, NIRISS, and MIRI) share the field of view of the Webb telescope optics, but they actually see different parts of the sky at any given observation. Credit: NASA
Webb’s mid-infrared instrument, MIRI, will be the last instrument that is aligned, as it is still waiting for the cryogenic cooler to chill it to its final operating temperature, just under 7 degrees above absolute zero. Interspersed within the initial MIMF observations, the two stages of the cooler will be turned on to bring MIRI to its operating temperature. The final stages of MIMF will align the telescope for MIRI.
You might be wondering: If all of the instruments can see the sky at the same time, can we use them simultaneously? The answer is yes! With parallel science exposures, when we point one instrument at a target, we can read out another instrument at the same time. The parallel observations don’t see the same point in the sky, so they provide what is essentially a random sample of the universe. With a lot of parallel data, scientists can determine the statistical properties of the galaxies that are detected. In addition, for programs that want to map a large area, much of the parallel images will overlap, increasing the efficiency of the valuable Webb dataset.
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard
This week the Webb team continued to make progress in aligning the telescope to the NIRCam instrument. Between taking the data to understand the optical components, we continue to check out the science instruments. The NIRSpec instrument includes a microshutter array of a quarter-million miniature movable windows, each 0.1 by 0.2 millimeters in size. The microshutter array allows scientists to target specific galaxies in fields they are studying, while closing the windows on the background or other objects which would contaminate the spectra. We have begun testing the mechanism and electronics that control and actuate the microshutters.
In recent weeks, we shared a technique for theoretically modeling the early universe. Today, we will discuss an observational program to help us answer some of those questions. Massimo Stiavelli, the Webb Mission Office head at the Space Telescope Science Institute, tells us about his planned investigations of the first stars and galaxies:
“The chemical composition of the early universe, just after the big bang, is the product of the nuclear processes that took place in the first few minutes of the universe’s existence. These processes are known as ‘primordial nucleosynthesis.’ One of the predictions of this model is that the chemical composition of the early universe is largely hydrogen and helium. There were only traces of heavier elements, which formed later in stars. These predictions are compatible with observations, and are in fact one of the key pieces of evidence that support the hot big bang model.
“The earliest stars formed out of material with this primordial composition. Finding these stars, commonly dubbed as the ‘First Stars’ or ‘Population III stars,’ is an important verification of our cosmological model, and it is within reach of the James Webb Space Telescope. Webb might not be able to detect individual stars from the beginning of the universe, but it can detect some of the first galaxies containing these stars.
“One way to confirm whether we are finding the first stars is to accurately measure metallicities of very distant galaxies. The astronomical term, metallicity, is a measurement of the amount of material heavier than hydrogen and helium – so a low metallicity galaxy would indicate it was made up of these ‘First Stars.’ One of the most distant galaxies discovered so far, known as MACS1149-JD1, is confirmed to be at redshift 9.1 and emitted the light we see when the universe was only 600 million years old. The light from this distant galaxy has been traveling ever since then and is just reaching us now.
“In the first year of Webb science, I have an observing program to study this galaxy and determine its metallicity. I will do this by attempting to measure the ratio in the strength of two spectroscopic lines emitted by oxygen ions, originally emitted at violet-blue and blue-green visible light (rest frame wavelengths at 4,363 angstroms and 5,007 angstroms). Thanks to cosmological redshift, these lines are now detectable at the infrared wavelengths that Webb can see. The use of a ratio of two lines of the same ion can provide an exquisite measurement of the gas temperature in this galaxy and, through relatively simple theoretical modeling, will provide a robust measurement of its metallicity.
“The challenge is that one of these lines is usually extremely weak. However, this line tends to get stronger at lower metallicity. So if we failed to detect the line and measure metallicity for MACS1149-JD1, that would likely mean that it has already been enriched by the heavier elements, and we need to look further and harder. Whether using my data or with future programs, I fully expect that during its operational lifetime Webb will be able to find objects with metallicity sufficiently low to hold keys for understanding the first generation of stars.”
–Massimo Stiavelli, Webb Mission Office head, Space Telescope Science Institute
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute
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.
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):
“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.
This NIRSpec diagram shows the placement of the Filter Wheel Assembly (FWA), a Grating Wheel Assembly (GWA), and a Refocus Mechanism Assembly (RMA). Credit: STScI
“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.
The NIRSpec thermal team from Airbus Germany of Taufkirchen and Immenstaad – Marc Maschmann (left), Martin Altenburg (right), and Ralf Ehrenwinkler (front) – at the Space Telescope Science Institute in Baltimore. Credit: STScI
“In the coming months, the NIRSpec team will continue their commissioning efforts. The whole team is very much looking forward to the start of science observations this summer!”
–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
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute
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.
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. 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.
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. 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.
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. 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.
This week, as the Webb team continues to make progress in aligning the telescope, other successful activities include the calibration of the NIRISS filter wheel and pupil wheel tuning for NIRCam. There are hundreds of activities like these planned during the commissioning process, and each is as important as the next to ensure that Webb can achieve its ambitious science goals. One such goal – detecting the earliest galaxies – also requires a lot of planning and theory to prepare for the observations. L.Y. Aaron Yung, a postdoc at NASA’s Goddard Space Flight Center, tells us more about the important theoretical work that helps plan for and then analyze galaxy surveys:
“This summer, Webb will start searching for galaxies in the distant universe. These highly anticipated observations are the key to unlocking the secrets in galaxy evolution and our universe’s history. Depending on the specific science goal of an observing program, the best-suited survey configurations can vary a lot.
“For instance, galaxy surveys going after the faintest and most distant galaxies require long exposure times (e.g., NGDEEP, PRIMER), but surveys for large-scale cosmological structure would require large survey areas (e.g., COSMOS-Web). Inputs from physically motivated simulations are essential to developing optimal observing strategies to achieve the specific scientific goals.
“To create a simulated universe, we first lay the foundation with dark matter concentrations, or halos, extracted from cosmological simulations. Dark matter accounts for 85% of the matter in the universe and has a dominant effect on the spatial distributions of galaxies across the universe. We then simulate the galaxies forming inside these dark matter halos based on astrophysical processes we learned from past observations.
“This figure illustrates an example of a portion of a simulated universe arranged in the shape of a cone traced by our sightlines. Because light travels at a finite speed, the light that originated in the early universe has travelled billions of years before finally reaching us today. This effectively allows us to look back in time and see the universe billions of years into its past.
Side-view of the simulated universe as presented in the “Semi-analytic forecasts for JWST” project (Yung et al., in preparation). Each data point represents a galaxy. Larger and darker data points represent galaxies with more mass, and vice versa. Credit: Yung et al.
“Our simulated universe serves as the basis to create mock observing fields that are statistically similar to the observed universe. The physically motivated models have been shown to match the galaxies observed by Hubble (e.g., the Hubble Ultra-Deep Field), and we use them to provide predictions for galaxies beyond Hubble’s capabilities.
View of the simulated universe from the front, just like the way we see the universe. The simulated field has perimeters similar to the Hubble Ultra-Deep Field. We also show a comparison of the simulated field at depths reachable by Hubble (left) and Webb (right). Credit: Yung et al.
“We process the simulated universe further into realistic mock images by adding effects from scientific instruments and survey configurations. These data products are used to support the development of the Webb data reduction pipeline and will inform the interpretation of future observations when they become available.
Synthetic image of an ultra-deep galaxy survey, with a side-by-side comparison at depths expected to be reached by CEERS (left) and NGDEEP (right). Courtesy of Micaela Bagley
“Webb will detect, for the first time in human history, galaxy populations forming shortly after the big bang, and theory is paving the way for the search. In turn, Webb observations will refine our understanding of galaxies and the history of our universe.”
–Dr. L. Y. Aaron Yung, NASA postdoctoral program fellow, NASA Goddard
As Webb continues its commissioning activities on the way to normal operations, we will start to preview anticipated science on this blog in addition to providing updates on the latest observatory activities.
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute
This early Webb alignment image, with dots of starlight arranged in a pattern similar to the honeycomb shape of the primary mirror, is called an “image array.” Credit: NASA/STScI/J. DePasquale
The Webb team continues to make progress in aligning the observatory’s mirrors. Engineers have completed the first stage in this process, called “Segment Image Identification.” The resulting image shows that the team has moved each of Webb’s 18 primary mirror segments to bring 18 unfocused copies of a single star into a planned hexagonal formation.
This image mosaic (top), which shows 18 randomly positioned copies of the same star, served as the starting point for the alignment process. To complete the first stage of alignment, the team moved the primary mirror segments to arrange the dots of starlight into a hexagonal image array (bottom). Each dot of starlight is labeled with the corresponding mirror segment that captured it. Credits: NASA (top); NASA/STScI/J. DePasquale (bottom)
With the image array complete, the team has now begun the second phase of alignment: “Segment Alignment.” During this stage, the team will correct large positioning errors of the mirror segments and update the alignment of the secondary mirror, making each individual dot of starlight more focused. When this “global alignment” is complete, the team will begin the third phase, called “Image Stacking,” which will bring the 18 spots of light on top of each other.
“We steer the segment dots into this array so that they have the same relative locations as the physical mirrors,” said Matthew Lallo, systems scientist and Telescopes Branch manager at the Space Telescope Science Institute. “During global alignment and Image Stacking, this familiar arrangement gives the wavefront team an intuitive and natural way of visualizing changes in the segment spots in the context of the entire primary mirror. We can now actually watch the primary mirror slowly form into its precise, intended shape!”
After starting the mirror alignment with Webb’s first detection of starlight in the Near-Infrared Camera (NIRCam), the telescope team is hard at work on the next steps for commissioning the telescope. To make more progress, the team needs to use another instrument, the Fine Guidance Sensor, to lock onto a guide star and keep the telescope pointed to high accuracy. We have asked René Doyon and Nathalie Ouellette of the Université de Montréal to explain how Webb uses its Canadian instrument in this process.
“After being powered on Jan. 28, 2022, and undergoing successful aliveness and functional tests, Webb’s Fine Guidance Sensor (FGS) has now successfully performed its very first guiding operation! Together with the Near-Infrared Imager and Slitless Spectrograph (NIRISS), the FGS is one of Canada’s contributions to the mission.
“To ensure Webb stays locked on its celestial targets, the FGS measures the exact position of a guide star in its field of view 16 times per second and sends adjustments to the telescope’s fine steering mirror about three times per second. In addition to its speed, the FGS also needs to be incredibly precise. The degree of precision with which it can detect changes in the pointing to a celestial object is the equivalent of a person in New York City being able to see the eye motion of someone blinking at the Canadian border 500 kilometers (311 miles) away!
“Webb’s 18 primary mirror segments are not yet aligned, so each star appears as 18 duplicate images. On Feb. 13, FGS successfully locked onto and tracked one of these star images for the first time. The FGS team was thrilled to see this ‘closed loop guiding’ working! From now on, most of the alignment process of the telescope mirrors will take place with FGS guiding, while NIRCam images provide the diagnostic information for mirror adjustments.”
–René Doyon, principal investigator for FGS/NIRISS, Université de Montréal; and Nathalie Ouellette, Webb outreach scientist, Université de Montréal
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute
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.
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.
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.
“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.
This image mosaic was created by pointing the 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. Credit: NASA
During the image capturing process that began Feb. 2, Webb was repointed to 156 different positions around the predicted location of the star and generated 1,560 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. “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.”
Lee Feinberg, Webb optical telescope element manager at NASA’s Goddard Space Flight Center, explains the early stages of the mirror alignment process.
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.
This “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 space. This configuration is not used during scientific operations and is used strictly for engineering and alignment purposes. In this case, the bright segment was pointed at a bright star, while the others aren’t currently in the same alignment. This image gave an early indication of the primary mirror alignment to the instrument. 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.
By Thaddeus Cesari, Webb science writer, NASA’s Goddard Space Flight Center, Greenbelt, Md.
