This article was originally published on Conversation. (opens in new tab) The publication added an article to Space.com Expert Voices: Op-Ed & Insights.
Marcia Rieke (opens in new tab)Regents Professor of Astronomy, University of Arizona
NASA is expected to release the first images taken by the James Webb Space Telescope on July 12, 2022.
They will mark the beginning of the next era in astronomy as the Web – the largest space telescope ever built – begins collecting scientific data to help answer questions about the earliest moments of the universe and allow astronomers to study exoplanets more closely than ever before. . But it took almost eight months of travel, tuning, testing and calibration to make sure this most valuable telescope was ready for impact time.
Marcia Rieke, astronomer from the University of Arizona (opens in new tab) and a scientist in charge of one of Web’s four cameras, explains what she and her colleagues did to launch this telescope.
Connected: NASA Space Telescope Mission James Web: Live updates
1. What has happened since the launch of the telescope?
After the successful launch of the James Webb Space Telescope on December 25, 2021, the team began a long process of moving the telescope to its final orbital position, disassembling the telescope and – as it cooled – calibrating the cameras and sensors on board.
The launch went as smoothly as the rocket launch could go. One of the first things my NASA colleagues noticed was that the telescope had more fuel remaining than anticipated for future adjustments to its orbit. This will allow the Web to run much longer (opens in new tab) from the mission’s original ten-year goal.
The first task during Webb’s lunar journey to his final location in orbit was to disassemble the telescope. This went without any problems, starting with the installation of the sun visor (opens in new tab) this helps cool the telescope, followed by aligning the mirrors and turning on the sensors.
When the sun visor was open, our team began monitoring the temperatures of the four cameras and spectrometers on board. (opens in new tab)waiting for them to reach low enough temperatures that we can begin testing each of the 17 different modes in which instruments can operate (opens in new tab).
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2. What did you test first?
Webcams cooled just as engineers had predicted, and the first instrument the team included was a close-up infrared camera – or NIRCam. NIRCam is designed to study the faint infrared light produced by the oldest stars or galaxies (opens in new tab) in the universe. But before he could do that, NIRCam had to help align 18 individual segments of the Web mirror.
When NIRCam cooled to minus 280 degrees Fahrenheit, it was cold enough to start detecting light reflected from Web’s mirror segments and producing the first images of the telescope. The NIRCam team was thrilled when the first light image arrived. We were in business!
These images showed that all the segments of the mirror were directed towards a relatively small area of the sky (opens in new tab)and the alignment was much better than the worst-case scenarios we had planned.
Webb’s fine guidance sensor also began operating at that time. This sensor helps keep the telescope steadily pointed at the target – similar to image stabilization in consumer digital cameras. Using the HD84800 star as a reference point, my colleagues at the NIRCam team helped choose the alignment of the mirror segments until it was practically perfect, far better than the minimum required for a successful mission. (opens in new tab).
3. Which sensors came to life next?
As the alignment of the mirrors was completed on March 11, the near-infrared spectrograph – NIRSpec – and the near-infrared image and slotless spectrograph – NIRISS – completed cooling and joined in the fun.
NIRSpec is designed to measure the strength of different wavelengths of light (opens in new tab) comes from the target. This information can reveal the composition and temperature of distant stars and galaxies. NIRSpec does this by looking at its target object through a slit that keeps other light out.
NIRSpec has multiple slots that allow it to view 100 objects at once (opens in new tab). Team members began testing multiple target modes, commanding slots to open and close, and confirmed that slots respond properly to commands. Future steps will measure exactly where the slots are directed and check if multiple targets can be observed simultaneously (opens in new tab).
NIRISS is a slotless spectrograph that will also break up light at different wavelengths, but it is better at observing all objects in the field, not just those in the slits. (opens in new tab). There are several modes of operation, including two that are designed specifically to study exoplanets particularly close to their parent stars.
So far, the instrument’s checks and calibrations have gone smoothly, and the results show that both NIRSpec and NIRISS will deliver even better data than engineers predicted before launch.
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4. Which instrument was last included?
The last launch tool on the Web was the Mid-Infrared Instrument, or MIRI. MIRI is designed to take photographs of distant or newly formed galaxies, as well as weak, small objects such as asteroids. This sensor detects the longest wavelengths of Web instruments and must be maintained at minus 449 degrees Fahrenheit (minus 267 degrees Celsius) – just 11 degrees F above absolute zero. If it were warmer, the detectors would only capture heat from the instrument itself, not interesting objects in space. MIRI has its own cooling system (opens in new tab)who needed extra time to become fully operational before the instrument was turned on.
Radio astronomers have found clues that there are galaxies completely hidden by dust and invisible to telescopes like Hubble (opens in new tab) which captures wavelengths of light similar to those visible to the human eye. Extremely low temperatures allow MIRI to be incredibly sensitive to light in the mid-infrared range, which can pass through dust more easily. When this sensitivity is combined with Web’s large mirror, it allows MIRI to penetrate these clouds of dust and detect stars and structures (opens in new tab) in such galaxies for the first time.
5. What’s next for the Web?
As of June 15, 2022, all of Web’s instruments have been turned on and made their first images. In addition, four recording modes, three time series modes and three spectroscopic modes have been tested and certified, leaving only three.
NASA plans to release a set of teaser observations on July 12 (opens in new tab) which illustrate Web’s abilities. This will show the beauty of Web images and also give astronomers a real taste of the quality of the data they will receive.
After July 12, the James Webb Space Telescope will start working full time on its scientific mission. A detailed schedule for next year has not yet been announced, but astronomers around the world are eagerly waiting to get the first data from the most powerful space telescope ever made.
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