James Webb Space Telescope Update: Fine Guidance Sensor Leads

Detail: The accuracy of the fine pointing sensor on the Webb telescope is impressive. Its ability to detect changes in a celestial object is said to be equivalent to the ability of a person in New York to see the eye movement of a person blinking at the Canadian border over 300 miles away.

The James Webb Space Telescope earlier this month began aligning its 18 mirrors, a mandatory multi-month process that involves the observatory’s Near Infrared Camera (NIRCam) instrument. After all, we saw what Webb saw when he looked at his first star.

That sample image confirmed that NIRCam was working correctly and that Webb was picking up light from the same star on each of its 18 primary mirror segments. And that’s exactly what we saw, one image with 18 seemingly randomly arranged dots of starlight.

The next step in the commissioning process involves using the telescope’s Fine Guidance Sensor (FGS) to acquire a guide star. The FGS measures the position of the guiding star in its field of view 16 times per second and sends the data to the sight’s precise guiding mirror approximately three times per second to maintain a stable target lock.

Moving forward, NASA has stated that most of the mirror alignment process will be done with FGS, and NIRCam images will be used to provide diagnostic information for further adjustments.