James Webb’s mirrors are perfectly aligned, what’s next?

The Nasa announced on Thursday 28 April that the alignment of mirrors of the James-Webb is now complete. Following a general review, all the teams unanimously concluded that the James Webb Space Telescope is fully capable of making observations and images with each of the instruments.

Aligning the mirrors took months, according to a procedure which had seven stages. It started with a rough alignment to ensure that the light received would reach the focal point. As a reminder, the primary mirror of the James-Webb is so wide – six meters in diameter – that it had to be folded to succeed in fitting everything into the fairing of the rocket. Ariadne 5 who sent him into space last Christmas.

The procedure then continued with the alignment of each of the eighteen hexagonal sections of the primary mirror, as well as the secondary mirror. The goal was to be able to stack the images received by each section into one. To continue, the teams refined the positions of the different sections of the primary mirror and then ensured that the optical path was optimal to each of the instruments. It was after a final series of iterations that the alignment procedure finally ended.

We remind you that all operations were done automatically remotely and with the utmost caution! In fact, we cannot set up a first aid operation from telescope as NASA has done on several occasions with Hubble using the space shuttle, or as proposed by the Chinese space agency by placing the future Xuntian space telescope on the same orbit that their space station. Converselythe James-Webb is much farther than low orbit, 1.5 million kilometers from Earth, at Lagrange point L2 of the Earth-Sun system.

Time for instrument testing!

The mirror alignment phase being finished, the James-Webb is fully operational. However, he is not yet ready to do science. There are still many tests to be carried out with the instruments. This new phase of preparation should last another two months according to NASA so that scientific operations begin in July.

From now on, the corrections on the mirrors will be very minimal, namely very small adjustments. The telescope already perfectly focuses the light on each of them, with optical performance “ beyond the most optimistic predictions of engineers according to NASA. However, the teams will check the alignment of the mirrors every two days and apply fixes if necessary. In addition, during the various tests of the instruments to come, the telescope will make many observations, which will allow engineers to confirm its proper functioning.

Each of the four scientific instruments is extremely complex. During the tests, a ballet of the different combinations they can have will take place in order to see if the lentils, sensors, masks, filter wheels and other equipment are working properly. Many calibrations are on the program.

In fact, the teams responsible for their instrument have already started testing for weeks, taking advantage of the images they can receive over the mirror alignment operations. But some instruments had to be put in special conditions to work well. This is the case of the Mirim instrument supplied by Cnes, which had to be cooled to just seven degrees above absolute zero, or -266° Celsius. This is ideal for eliminating any noise in an infrared signal and is essential for obtaining data that meets the expectations of scientists.

The four instruments will be used to observe the Universe in infrared. NIRCam is a wide field camera observing in wavelengths between 0.6 and 5 microns. NIRSpec is his companion spectrometer to analyze infrared signals from compact sources and distant galaxies. Mirim observes in the mid-infrared (between 5 and 28 microns), which is interesting for analyzing interstellar clouds composed of gas and dust. Finally, NIRISS is a secondary instrument that can make spectra large field.

The James-Webb Space Telescope aligns its mirrors

Article of Daniel Christianpublished on March 7, 2022

This is a setting for any telescope, whether it’s your niece’s or the most powerful space telescope ever sent in history. Since the James-Webb managed to capture its first photonsthe teams follow this long process of three months which will end in the spring.

A month ago, NASA announced that the NIRCam instrument (infrared camera), the main imager of the James-Webb, detected its first rays of light. This means that the rays have traveled the entire intended path through the telescope, guided by the various mirrors of structure. Since, the Nasa team began aligning the 18 sections of the primary mirror.

The work is extremely precise, given the scientific requirements of the American space telescope. To imagine it, you have to imagine that if the primary mirror is the size of the United States, each section would be the size of Texas, and you would have to adjust their height with a precision of 3.8 centimeters!

The process has seven phases. At the end of February, the team completed phases two and three. These two phases consisted of refining the alignments of each section and the secondary mirror, then stacking the images received by each section into a single image.

Fourth phase initiated

These are now “coarse” alignments before moving on to phase five, which consists of refining the position of the sections of the primary mirror. These two phases should last several weeks. The next step will consist of aligning the mirrors with the fields of view of the scientific instruments. Finally, the last phase will consist of final corrections in an iterative way. So, according to NASA, the telescope will be operational in the spring, but it will be necessary to wait until the end of the summer to have the maximum quality.

While waiting for phase five, NASA has announcement that the team of spectrograph in the European near infrared NIRSpec of the James-Webb has successfully verified three mechanisms essential to the proper functioning of the instrument.