📘 Definition
Sun sensors are among the simplest and most reliable attitude sensors on a spacecraft. Coarse sun sensors (CSS) use photodiodes on each face of the satellite to determine which side is sun-lit — providing 5° accuracy, enough for safe-mode operations. Fine sun sensors (FSS) use a slit or pinhole and a position-sensitive detector to measure the sun angle with 0.01–0.1° precision. Sun sensors are critical for solar array pointing (maximising power generation) and for safe-mode attitude acquisition when more complex sensors (star trackers) are unavailable. Nearly every satellite carries sun sensors as a baseline attitude reference.
5° accuracy
Coarse (CSS)
0.01–0.1°
Fine (FSS)
Photodiodes / position detector
Method
Solar array pointing, safe mode
Key Use