How does a star tracker determine spacecraft attitude?

Star trackers are optical sensors that determine attitude by imaging stars and matching patterns to a star catalog. Operation: CCD/CMOS sensor images star field, Software identifies stars and measures centroid positions, Pattern matching algorithm compares to onboard star catalog, and Attitude calculated from identified star positions. Accuracy: 1-10 arcseconds typical, enabling precise pointing. Advantages: Autonomous operation, High accuracy, No drift over time. Limitations: Cannot operate with Sun in field of view, Blinding during maneuvers (star trails), and Processing time for lost-in-space acquisition. Typically 2+ star trackers for redundancy and continuous coverage. Modern star trackers fit in CubeSat form factor. Integration with gyros (star tracker updates, gyros propagate between updates) provides optimal attitude determination.