Last-minute announcement: James Webb Telescope used a second tool in the process of aligning mirrors. See here

17/02/2022
Credit: NASA - The FGS/NIRISS at NASA Goddard before integration into the instrument module.
Credit: NASA - The FGS/NIRISS at NASA Goddard before integration into the instrument module.

Last-minute announcement from NASA: James Webb Telescope used a second tool in the process of aligning mirrors. The US space agency, NASA, has just announced that the James Webb Telescope has successfully used the second instrument of its own to help position and straighten mirrors. 

The near-infrared camera (NIRCam) was the first instrument used to determine the position of Webb's mirrors by detecting the first stellar light (Webb's first image, see here). NASA has used NIRCam a lot, but now it is taking new steps, and in order to make more progress, a second tool must be used, namely the fine guidance sensor. 

Thus through this tool of Web (fine guidance sensor), the team that coordinates it from Earth, will lock onto a guide star and so will keep the telescope pointed to high accuracy.

René Doyon, principal investigator for FGS/NIRISS, Université de Montréal and Nathalie Ouellette, Webb outreach scientist, Université de Montréal will explain below about this new tool used in the process of aligning mirrors.

"After being powered on Jan. 28, 2022, and undergoing successful aliveness and functional tests, Webb's Fine Guidance Sensor (FGS) has now successfully performed its very first guiding operation! Together with the Near-Infrared Imager and Slitless Spectrograph (NIRISS), the FGS is one of Canada's contributions to the mission.

"To ensure Webb stays locked on its celestial targets, the FGS measures the exact position of a guide star in its field of view 16 times per second and sends adjustments to the telescope's fine steering mirror about three times per second. In addition to its speed, the FGS also needs to be incredibly precise. The degree of precision with which it can detect changes in the pointing to a celestial object is the equivalent of a person in New York City being able to see the eye motion of someone blinking at the Canadian border 500 kilometers (311 miles) away!

"Webb's 18 primary mirror segments are not yet aligned, so each star appears as 18 duplicate images. On Feb. 13, FGS successfully locked onto and tracked one of these star images for the first time. The FGS team was thrilled to see this 'closed loop guiding' working! From now on, most of the alignment process of the telescope mirrors will take place with FGS guiding, while NIRCam images provide the diagnostic information for mirror adjustments."

Article by: Andacs Robert Eugen, on 17 February 2022, at 09:29 am Los Angeles time

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