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James Webb Space Telescope
FGS - Fine Guidance Sensor

Find Guidance System

The FGS is a sensitive camera that provides dedicated, mission-critical support for the observatory's Attitude Control System (ACS). The camera can image two adjacent fields of view, each approximately 2.4' X 2.4' in size, and can also be configured to read out small 8 X 8 pixel subarrays at a rate of 16 times per second. Even with these short integration times, the FGS is sensitive enough to reach 58 µJy at 1.25 µm (~Jab = 19.5). This combination of sky coverage and sensitivity ensures that an appropriate guide star can be found with 95% probability at any point in the sky, including high galactic latitudes.

The main functions of FGS include obtaining images for target acquisition, acquiring pre-selected guide stars and to provide the ACS with centroid measurements of the guide stars at a rate of 16 times per second. During on-orbit commissioning of the JWST, the FGS will also provide pointing error signals during activities to achieve alignment and phasing of the segments of the deployable primary mirror.

A science instrument known as the Near-InfraRed Imager and Slitless Spectrograph (NIRISS) is packaged with the guide camera, but is functionally independent.

The Canadian Space Agency will provide the Fine Guidance Sensor/NIRISS to the the JWST Project. The prime contractor is Com Dev. The Principal Investigator for the FGS is Chris Willott of the Herzberg Institute of Astrophysics, National Research Council of Canada.

Latest News

2015 February 12
FGS/NIRISS became the first instrument to be reinstalled in the Integrated Science Instrument Module (ISIM) following the "Half-Time Show." All the planned hardware changes were successfully completed and both instruments passed their electronic check-outs at room temperature with flying colors. FGS/NIRISS is ready for the final series of tests at NASA's Goddard Space Flight Center!

NIRISS at GSFC cleanroom

2014 December 17
Karl Saad, the Canadian Space Agency’s Project Manager for FGS/NIRISS, visited STScI to discuss plans for post-launch commissioning with the CSA-sponsored Instrument Scientists and other members of the FGS/NIRISS Team. Pictured from left-to-right are: Swara Ravindranath, André M., Karl Saad, and Pierre Chayer.

CSA Scientists

2014 December 10
“Half-Time Show” activities for FGS/NIRISS began with the removal of the flight hardware from the Integrated Science Instrument Module (ISIM) in the large cleanroom at NASA’s Goddard Space Flight Center. The picture shows the moment of extraction, as captured by the ISIM WebbCam. The “Half-Time Show” is a busy time for the COM DEV team, since it represents the final opportunity to replace inferior hardware. For FGS, the priority is to replace both detectors and some of the read-out circuitry. Although it was the last package to be removed from ISIM, FGS/NIRISS will be the first to be reinstalled later in January.

FGS/NIRISS at GSFC cleanroom

2014 September 23
The FGS/NIRISS Instrument Teams at STScI proudly display their "Significant Achievement Awards" from the NASA JWST Project. The certificates recognize the Team's "extraordinary dedication and contributions" to NIRISS/FGS. Pictured from left-to-right are: Anand Sivaramakrishnan; Sherie Holfeltz; Alex Fullerton; Deepashri Thatte; Kevin Volk, André M., Swara Ravindranath; Paul Goudfrooij; Pierre Chayer; and Van Dixon. Missing: Ed Nelan (Photo by Michael Wolfe). What a Team!


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