What is a Star Tracker on a Satellite?

Satellites must determine their attitude with extremely high precision to successfully complete various missions. The star tracker plays a crucial role in achieving this accurate attitude control.

A star tracker is a high-precision optical attitude measurement instrument. It captures images of the star field, identifies the stars, and matches them against an onboard star catalog. In this way, it determines the satellite’s three-dimensional orientation (attitude) in real time.

Main Components of a Star Tracker

– Optical system: It includes a wide-field or narrow-field lens, optical filter, and stray-light baffle.

– Image sensor: Most modern units use radiation-hardened scientific-grade CMOS or CCD detectors.

– Image processing and attitude computation unit: A high-performance embedded processor or FPGA runs complex algorithms for star extraction, star pattern recognition, and attitude calculation.

– Built-in star catalog: It usually contains the positions, magnitudes, and colors of 5,000 to 30,000 bright stars.

– Structure and thermal control: Lightweight aluminum alloy or carbon fiber structure combines with passive or active thermal control measures.

Main Advantages of Star Trackers

– Star trackers provide extremely high absolute accuracy. Commercial models typically achieve 1–10 arcseconds, while high-end units can reach sub-arcsecond precision (

– They operate fully autonomously. They do not rely on Earth, Sun, or any external beacons, so they work independently even in deep space.

– Unlike gyroscopes, star trackers show no cumulative drift. Therefore, they serve as an ideal long-term attitude reference.

– Modern small star trackers consume relatively low power. Their average power usage is only 1–5 W, which makes them very suitable for small satellites and CubeSats.

– Specially designed space-grade star trackers resist radiation very well. They can operate reliably in high orbits or deep space for more than 10 years.