3. Star sensors

Star sensors, more commonly known as star sights, measure the coordinates of one or more stars in a frame of reference linked to the spacecraft. This data is supplied to a computing unit (integrated into the sensor or external to it), enabling attitude information to be restored by comparing the measured directions with those of known stars, given by a star catalog adapted to the mission in question.

Due to the nature of the celestial bodies observed, star sensors are the most accurate of all attitude sensors, achieving arc-second accuracies. On the other hand, they are generally heavier, more expensive and require greater electrical power than most other attitude sensors. What's more, they require more or less sophisticated processing software, which must be integrated into high-performance computing systems, either built into the sensor itself, or external to...