Get ready for a new way of seeing the universe

The James Webb Space Telescope (JWST) is next to NASA’s Great Observatories; following along the lines of the Hubble Space Telescope, the Compton Gamma-ray Observatory, the Chandra X-ray Observatory and the Spitzer Space Telescope. JWST combines the qualities of two of its predecessors, observing in infrared light, like Spitzer, with fine resolution, like Hubble. Credit: NASA, SkyWorks Digital, Northrop Grumman, STScI

1. What happened since the launch of the telescope?

After the successful launch of the James Webb Space Telescope on December 25, 2021, the team began the long process of moving the telescope to its final orbital position, unfolding the telescope and – as everything cooled down – calibrating the cameras and sensors. on board.

The launch was as smooth as a rocket launch can get. One of the first things my colleagues at NASA noticed was that the telescope had more fuel left on board than anticipated to make future adjustments to its orbit. This will allow Webb to operate much longer than the mission’s initial 10-year goal.

The first task during Webb’s month-long journey to its final location in orbit was to deploy the telescope. This went off without a hitch, starting with deploying the sun shield that helps cool the telescope, followed by aligning the mirrors and activating the sensors.

Once the sunshield was open, our team began monitoring the temperatures of the four cameras and spectrometers on board, hoping they would reach temperatures low enough that we could begin testing each of the 17 different modes in which the instruments can operate.


NIRCam, seen here, will measure infrared light from extremely distant and ancient galaxies. It was the first instrument to go online and helped to align the 18 mirror segments. Credit: NASA/Chris Gunn

2. What did you test first?

The cameras on the Webb cooled down just as the engineers predicted, and the first instrument the team turned on was the Near Infrared Camera – or NIRCam. NIRCam was 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 the 18 individual segments of the Webb mirror.

Once NIRCam cooled to minus 280 F, it was cool enough to begin detecting light reflected from Webb’s mirror segments and producing the telescope’s first images. The NIRCam team was ecstatic when the first light image arrived. We were in business!

These images showed that the mirror segments were all pointing to a relatively small area of ​​the sky, and the alignment was much better than the worst-case scenarios we had planned.

Webb’s fine orientation sensor also came into operation at this time. This sensor helps keep the telescope firmly pointing at a target – much like image stabilization in consumer digital cameras. Using the HD84800 star as a reference point, my colleagues on the NIRCam team helped adjust the alignment of the mirror segments until it was virtually perfect, far better than the bare minimum needed for a successful mission.

3. Which sensors came to life next?

When the mirror alignment ended on March 11, the Near Infrared Spectrograph – NIRSpec – and the Near Infrared Imager and Slitless Spectrograph – NIRISS – finished cooling off and joined the party.

NIRSpec is designed to measure the intensity 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 a slit that keeps light out.

NIRSpec has several slits that allow you to see 100 objects at once. Team members began testing the multi-target mode, commanding the rifts to open and close, and confirmed that the rifts were responding correctly to commands. Future steps will measure exactly where the slits are pointing and verify that multiple targets can be observed simultaneously.

NIRISS is a slitless spectrograph that also breaks light into its different wavelengths, but is best for observing all objects in a field, not just those in the slits. It has several modes, including two specifically designed to study exoplanets particularly close to their parent stars.

So far, instrument checks and calibrations are going smoothly, and the results show that both NIRSpec and NIRISS will provide even better data than engineers predicted before launch.

Comparative Image Webb MIRI and Spitzer

The MIRI camera, image on the right, allows astronomers to see through clouds of dust with incredible clarity compared to earlier telescopes like the Spitzer Space Telescope, which produced the image on the left. Credit: NASA/JPL-Caltech (left), NASA/ESA/CSA/STScI (right)

4. What was the last instrument to be turned on?

The final instrument to boot into Webb was the Mid-Infrared Instrument, or MIRI. MIRI is designed to take pictures of distant or newly formed galaxies, as well as small, faint objects such as asteroids. This sensor detects the longer wavelengths of Webb instruments and should be kept minus 449 F – just 11 degrees F above

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