May 15, 2024

James Webb Space Telescope Locked Onto Guide Star for High Accuracy Mirror Alignment

Credit: NASAs Goddard Space Flight Center
After beginning the mirror positioning with Webbs first detection of starlight in the Near-Infrared Camera (NIRCam), the telescope team is hard at work on the next actions for commissioning the telescope. To make more progress, the group needs to use another instrument, the Fine Guidance Sensor, to lock onto a guide star and keep the telescope pointed to high accuracy. We have actually asked René Doyon and Nathalie Ouellette of the Université de Montréal to discuss how Webb uses its Canadian instrument in this process.
” After being powered on January 28, 2022, and going through effective aliveness and practical tests, Webbs Fine Guidance Sensor (FGS) has actually now effectively performed its extremely first assisting operation! Together with the Near-Infrared Imager and Slitless Spectrograph (NIRISS), the FGS is among Canadas contributions to the mission.
” To guarantee Webb remains locked on its celestial targets, the FGS determines the exact position of a guide star in its field of vision 16 times per second and sends modifications to the telescopes great steering mirror about three times per second. In addition to its speed, the FGS also requires to be incredibly accurate. The degree of precision with which it can discover changes in the indicating a celestial things is the equivalent of a person in New York City being able to see the eye movement of somebody blinking at the Canadian border 500 kilometers (311 miles) away!

By NASA
February 17, 2022

” Webbs 18 main mirror segments are not yet lined up, so each star appears as 18 duplicate images. From now on, most of the positioning procedure of the telescope mirrors will take place with FGS guiding, while NIRCam images provide the diagnostic details for mirror modifications.”
— René Doyon, primary investigator for FGS/NIRISS, Université de Montréal; and Nathalie Ouellette, Webb outreach scientist, Université de Montréal

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After starting the mirror alignment with Webbs first detection of starlight in the Near-Infrared Camera (NIRCam), the telescope team is hard at work on the next steps for commissioning the telescope.” To guarantee Webb remains locked on its celestial targets, the FGS measures the specific position of a guide star in its field of view 16 times per second and sends changes to the telescopes great steering mirror about 3 times per second.” Webbs 18 main mirror sections are not yet lined up, so each star appears as 18 duplicate images.

Jonathan Gardner, Webb deputy senior job researcher, NASAs Goddard Space Flight
And Alexandra Lockwood, job scientist for Webb science communications, Space Telescope Science Institute