📘 Definition
The Attitude Determination and Control System (ADCS) keeps a satellite correctly oriented in space. Determination uses sensors: star trackers (most accurate), sun sensors, Earth horizon sensors, magnetometers, and gyroscopes. Control uses actuators: reaction wheels (precise but build momentum), magnetorquers (use Earth's magnetic field to dump momentum), control moment gyroscopes (for large spacecraft), and thrusters (for rapid slewing or momentum dumping). Earth observation satellites require pointing accuracy of 0.01° or better; communications satellites need their antennas aimed within fractions of a degree.
Star trackers, sun sensors, gyros
Sensors
Reaction wheels, magnetorquers
Actuators
0.01°
EO Accuracy
0.05–0.1°
Comms Accuracy