NASA is set to release the first images captured by the James Webb Space Telescope on July 12, 2022. It will mark the beginning of the next era in astronomy as Webb – the largest space telescope ever built – begins to collect scientific data that will help answer questions about the first moments to the universe and allow astronomers to study the exoplanets in greater detail than ever before. But it took nearly eight months of travel, setup, testing and calibration to make sure these most valuable telescopes were ready for prime time. Marcia Rickey, an astronomer at the University of Arizona and the scientist in charge of one of the four webcams, explains what she and her colleagues were doing to set up and operate this telescope.
1. What has happened since the telescope was launched?
After the successful launch of the James Webb Space Telescope on December 4th. On the 25th of 2021, the team began the long process of moving the telescope to its final orbital location, opening the telescope – and as everything cooled – calibrating the cameras and sensors on board.
The launch was as smooth as a missile launch can happen. One of the first things my NASA colleagues noticed was that the telescope had more fuel left on board than expected for future adjustments to its orbit. This will allow Webb to operate for much longer than the mission’s initial goal of 10 years.
The first task during Webb’s month-long journey to his final position in orbit was to open the telescope. This proceeded without any hits, starting with the deployment of the white joint of the sun shield that helps cool the telescope, followed by the alignment of the mirrors and the operation of the sensors.
Once the sun shield was opened, our team began monitoring the temperatures of the four cameras and spectrometers on board, waiting for them to reach temperatures low enough so that we could begin testing each of the 17 different modes in which the devices could operate.
2. What did you test first?
The cameras on Webb cooled just as the engineers had expected, and the first instrument the team turned on was the near-infrared camera — or NIRCam. NIRCam is designed to study the faint infrared light produced by the oldest stars or galaxies in the universe. But before it could do that, NIRCam had to help align 18 individual segments of a Web mirror.
Once the NIRCam cooled to 280 degrees Fahrenheit, it was cold enough to begin detecting light reflected off the Webb mirror clips and producing the telescope’s first images. The NIRCam team was ecstatic when the first scans arrived. We were in business!
These images showed that all parts of the mirror were pointing at a relatively small area of the sky, and the alignment was much better than our planned worst-case scenario.
Webb’s precision-guidance sensor also came into play at this time. This sensor helps keep the telescope firmly pointed at the target – much like image stabilization in consumer digital cameras. Using the star HD84800 as a reference point, I helped my NIRCam teammates connect to align mirror segments until they were nearly perfect, far better than the minimum required for a successful mission.
3. What sensors came alive after that?
As the mirror alignment wrapped up on March 11, the near-infrared spectrometer – NIRSpec – and the near-infrared imager and spectrograph – NIRISS – finished cooling off and joined the party.
NIRSpec is designed to measure the strength of different wavelengths of light coming from a target. This information can reveal the composition and temperature of distant stars and galaxies. NIRSpec does this by looking at the target object through an aperture that blocks other light.
NIRSpec has multiple slots that allow it to look at 100 items at once. Team members began testing the position of the multiple targets, instructed the slots to open and close, and confirmed that the slots were responding correctly to commands. Future steps will measure exactly where the cracks are pointing and verify that multiple targets can be observed simultaneously.
NIRISS is a slit-free spectrometer that also splits light into different wavelengths, but is better at observing all objects in the field, not just those in slits. It has several modes, including two that are specifically designed to study exoplanets that are particularly close to their parent stars.
So far, device checks and calibrations have continued smoothly, and the results show that both NIRspec and NIRISS will provide better data than engineers expected before launch.
4. What was the last tool you run?
The last tool to boot on Webb was the mid-infrared instrument, or MIRI. MIRI is designed to capture images of distant or newly formed galaxies as well as faint small objects such as asteroids. This sensor detects the longest wavelengths of Webb’s instruments and must be kept at 449 degrees Fahrenheit – just 11 degrees Fahrenheit above absolute zero. If it’s warmer, the detectors will only pick up heat from the device itself, not the interesting stuff in space. MIRI has its own cooling system, which needs additional time to run at full capacity before turning on the equipment.
Radio astronomers have found hints of galaxies completely hidden by dust and undetectable by telescopes like the Hubble that pick up wavelengths of light similar to those visible to the human eye. The extremely cold temperatures allow MIRI to be incredibly sensitive to light in the mid-infrared range that can pass through dust more easily. When combined with this sensitivity and Webb’s large mirror, it allows MIRI to penetrate these dust clouds and reveal stars and structures in such galaxies for the first time.
5. What’s next for Webb?
As of June 15, 2022, all Webb tools are up and running and have taken their first images. In addition, four imaging modes, three time-series modes, and three spectral modes were tested and approved, leaving only three modes.
On July 12, NASA plans to release a set of teaser notes detailing Webb’s capabilities. These images will show off the beauty of Webb’s images and will also give astronomers a real taste of the quality of the data they will get.
After July 12, the James Webb Space Telescope will begin working full time on its science mission. The detailed timeline for the coming year has yet to be released, but astronomers around the world are eagerly awaiting the recovery of the first data from the most powerful space telescope ever built.