What methods are used for spacecraft attitude determination?

Attitude determination methods vary in accuracy and autonomy: Vector observation - Star trackers (arcsecond accuracy, autonomous), Sun sensors (degree accuracy, simple), Earth/horizon sensors (degree accuracy), and Magnetometers (degree accuracy, requires model). Rate sensing - Gyroscopes measure rotation rate, integrated for attitude, but drift over time; used for propagation between absolute updates. Algorithm methods: TRIAD (two-vector attitude determination), QUEST/q-method (optimal quaternion from multiple vectors), and Kalman filtering (fuses multiple sensors, estimates biases). Sensor selection based on: Accuracy requirements, Cost and mass constraints, Pointing requirements (continuous vs periodic), and Fault tolerance needs. Typical configuration: Star trackers for accuracy, Sun sensors for safe mode, magnetometer for coarse determination, and gyros for high-rate maneuvering.