Canada's stellar navigator on the James Webb Space Telescope

The James Webb Space Telescope will be the most important space observatory of the next decade, serving astronomers from all over the world. One of the two Canadian elements on the James Webb Space Telescope, the Fine Guidance Sensor (FGS) is the most sophisticated guidance sensor of any telescope ever built. It locks on to bright stars in deep space to keep Webb's images sharp. (Credit: Canadian Space Agency)

The Fine Guidance Sensor (FGS) is the most sophisticated guidance sensor of any telescope ever built. It locks on to bright stars in deep space to keep Webb's images sharp.

What does the Fine Guidance Sensor do?

• Identifies and locks on to preselected guide stars
• Tracks objects in our solar system with high precision
• Keeps Webb's gaze perfectly aligned

The FGS consists of two identical cameras that are critical to Webb's ability to "see." The FGS can select a star from a catalogue of nearly one billion guide stars. These known cosmic reference points enable Webb to calculate its position in space.

A watchful guide

The FGS remains active during all of Webb's observations. It provides Webb's stability system with extremely precise data 16 times per second.

The Canadian-made sensor is so sensitive that it can detect a tiny angular displacement equivalent to the thickness of a human hair as seen from one kilometre away. That's like spotting someone blink in Toronto, all the way from Montreal!