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James Webb Space Telescope mounted on a guide star for high precision mirror alignment

Credit: NASA’s Goddard Space Flight Center

After start aligning the mirror with Webb’s first detection of starlight in a near-infrared camera (NIRCam), the telescope team is working diligently on the next steps to commission the telescope. To make more progress, the team must use another tool, a thin guidance sensor, to capture the guide star and keep the telescope pointing up.[{” attribute=””>accuracy. We have asked René Doyon and Nathalie Ouellette of the Université de Montréal to explain how Webb uses its Canadian instrument in this process.

“After being powered on January 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 February 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.”

René Doyon, principal investigator for FGS/NIRISS, Université de Montréal; and Nathalie Ouellette, Webb outreach scientist, Université de Montréal

Author:

  • Jonathan Gardner, Deputy Senior Research Fellow, Webb Project, NASAGoddard Space Flight Center
  • And Alexandra Lockwood, Webb Scientific Communications Project Scientist, Space Telescope Science Institute



https://scitechdaily.com/james-webb-space-telescope-locked-onto-guide-star-for-high-accuracy-mirror-alignment/ James Webb Space Telescope mounted on a guide star for high precision mirror alignment

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