James Webb Telescope: aligning its mirrors will be long and laborious
Nasa had identified no less than 344 problems likely to arise during the launch of the James Webb Telescope. In the end, everything went smoothly. On December 25, the stargazer was successfully launched from Guyana by an Ariane 5 ECA rocket. Ultimately, the JWST will allow astronomers to understand how the first stars and galaxies formed following the Big Bang. The information collected should also shed light on the mysteries surrounding the three supermassive blacks, dark energy but also the formation of planets.
On January 4, the critical step of deploying the James Webb's sun visor was successfully completed. Now it's all about properly aligning the 18 hex segments of the primary and secondary mirrors. The latter were folded in order to be able to survive take-off. To prepare for its arrival in orbit around the Lagrange point L2, NASA astronomers will therefore use the NIRCam infrared camera to precisely refine the position of the segments. The ultimate goal is to allow the segments to collect light efficiently.
James Webb Telescope: NASA must operate the mirrors "like a choir"
At a press conference, engineers from the space agency indicated that it will be a long and tedious process. This one will require several blurry and “ugly” test images to make sure everything goes as planned. By doing so, the mirrors should be correctly aligned around April 24th. "It's as if we had 18 mirrors which are, at the moment, little prima donnas (lead singer of an opera, editor's note), each singing its own melody in any key", points out astronomer Jane Rigby. And to continue to spin his musical comparison: “We have to make them work like a choir, and it is a methodical and laborious process. »
Each mirror is moved by computer-controlled actuators. And the adjustments can be as little as 10 nanometers. “Currently, we use these actuators to make adjustments of more than one centimeter,” NASA points out on its blog. And to emphasize that these will be the most significant movements that the actuators will make on the telescope.
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The task is time-consuming because the scientists will proceed in a very gradual manner, with only one actuator operating at a time. A simpler and safer method, as computers and sensors can closely monitor the maneuvers in progress. What's more, it limits the amount of heat emitted by the actuator motors on the very cold mirrors of the telescope. “Thus, these large movements of 12.5 millimeters for each segment are divided into very many short movements carried out by the actuators in turn”, indicates the space agency. “At full speed, it takes about a day to move all the segments by just 1 millimeter. That's about the same speed grass grows."
Source: NASA