This image confirms the correct calibration of the James Webb Space Telescope.

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The JWST Space Telescope has almost completed the phase of aligning its primary mirror segments to provide unprecedented images of the universe. After a few additional adjustments, the observatory will finally be able to carry out its mission.

Image of the James-Webb primary mirror segment alignment evaluation. © NASA-STSCI

The James-Webb telescope, placed for several weeks at the L2 Lagrange point, has just successfully completed a new calibration step that brings it closer to final use. Indeed, its main mirror, divided into 18 segments, is almost ideally positioned for high resolution infrared and near infrared scanning of space. The first “real” results should be made public by NASA in the summer of 2022. Meanwhile, on Friday, March 11, JWST was able to capture the star 2MASS J17554042+6551277, which was used for pointing.

The bright spots around are nothing but galaxies and other stars in the background. Attention, whether it’s with Hubble or James-Webb, capturing images – and related scientific data – doesn’t quite work like a regular camera, because adjusting everything becomes extremely difficult due to the 1.5 million kilometers that separate us. from car.

The entire calibration process was divided into seven steps, NASA scientists explain. Of course, each of these operations is critical, but they also need to be flexible or repeatable.

1. Segment identification

Each of the 18 segments sends back its own image of the target star in disarray. The resulting image then shows some kind of constellation. By moving the segments one by one, you can identify them.

Over 1,560 images were taken to capture this image by adjusting the position of the telescope, totaling over 2 billion pixels.  © NASA

Over 1,560 images were taken to capture this image by adjusting the position of the telescope, totaling over 2 billion pixels. © NASA

2. Align segments

Once identified, they are aligned, correcting the most important errors. The captured image suggests a hexagon. Then there is a debugging phase and a more accurate error calculation is performed.

When the segments are first aligned, the 18 grips take on the shape of a hexagon, requiring a first focus.  © NASA

When the segments are first aligned, the 18 grips take on the shape of a hexagon, requiring a first focus. © NASA

3. Convergence of rays

In order to collect the different received iterations, all the received light must converge at one point. The segments, divided into three groups, sequentially change their position to create a “single image”.

This simulation shows convergence step by step by adjusting the primary mirror segments.  © NASA

This simulation shows convergence step by step by adjusting the primary mirror segments. © NASA

4. Initial setup

Although considered “rude” (rude in English), the new correction phase only works on a few tens of micrometers. Segment placement changed vertically instead of “behave like 18 small individual telescopes”segments should be one after this step.

5. Precise fit

This sequence allows you to calculate and correct errors in order to get rid of them. in the end in perfect focus. It also uses the method used in the segment alignment step. On the other hand, new special tools are used to better customize the position of the different segments. It was at the end of this phase that we were able to discover the first “clear” image of James-Webb.

6. Adjustment of the telescope according to the field of view

Now that the segments are correctly adjusted, it’s a matter of checking that they work correctly with all on-board instruments and in all possible configurations. Thus, several captures are made with different parameters and sensors. If errors are found, additional corrections are made.

7. Repeat alignment for final fixes.

After applying the new corrections obtained in the previous step, the last tuning step consists of making several final corrections to the primary segments. Fine tuning procedures are reused. A quality control phase is also performed with every scientific instrument.

Extraordinary project

The launch of the James Webb Space Observatory took place on December 25, 2021, and its deployment in early January 2022, after more than three decades of development and many delays. Unusually, the telescope weighs over 6.2 tons and has a wingspan of 22 meters with a heat shield.

As often, the mission was completed thanks to the international collaboration of the American NASA, the European ESA and the Canadian CSA. In a few months, James-Webb will be up and running with real observations of the distant universe (thus in the past), galaxies, exoplanets, nebulae, etc.

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