Star Tracker
A optical sensor that determines a spacecraft's orientation by photographing star fields and matching them against an onboard star catalog.
Explanation
A star tracker takes an image of the sky, identifies known star patterns (asterisms), and computes the spacecraft's attitude in three axes by comparing the observed positions with a pre-loaded star catalog. Modern star trackers achieve accuracy of 1-10 arcseconds — far better than Sun sensors or magnetometers. They are essential for missions requiring precise pointing, such as Earth observation at sub-meter GSD, astronomical telescopes, and laser communications. Star trackers must contend with stray light (Sun, Moon, Earth albedo), radiation damage on sensors, and high rotation rates that smear star images. They typically operate in a lost-in-space mode (initial acquisition) and a tracking mode (maintaining attitude from frame to frame). Most satellites carry two or more star trackers for redundancy. The technology has matured significantly: commercial off-the-shelf star trackers are now available from multiple vendors for CubeSats and larger spacecraft.
Why It Matters
Star trackers provide the most accurate attitude determination available for spacecraft. They are essential for imaging, communications, and science missions, and their miniaturization has enabled small satellites to achieve precision pointing.
Concept Map
How Star Tracker connects to other glossary terms:
Frequently Asked Questions
Do star trackers work during the day?
They work on the day side of Earth, but they can be blinded by direct sunlight, Earth albedo, or the Moon in the field of view. Baffles and sun-avoidance logic mitigate this.
How many stars does a star tracker need to see?
Typically 5-10 bright stars are sufficient for a robust attitude solution. Star catalogs onboard contain 5,000-20,000 stars.
Sources
Last updated: July 1, 2026