📘 Definition
A star tracker is an optical sensor that images a portion of the sky, identifies star patterns using an onboard catalogue, and computes the satellite's absolute orientation (attitude) in inertial space. Modern star trackers achieve accuracy of 1–10 arcseconds — far more precise than sun sensors or magnetometers. Most satellites carry at least two star trackers for redundancy and to avoid gaps when the Sun, Moon, or Earth blocks one sensor's field of view. Star trackers are critical for high-precision Earth observation (where pointing accuracy directly determines image geolocation) and for space telescopes.
1–10 arcseconds
Accuracy
Star pattern matching
Method
2–3 per satellite
Typical Count
Sun, Moon, Earth in FOV
Blinding