Earth Sensors

Abstract

Earth sensors were some of the earliest spacecraft sensors. Many early satellites were for communications or Earth observations, so the most important thing was to point the satellite at the Earth, that is, to null the roll and pitch errors. In many cases, the yaw error was not important or could be controlled through the momentum of the satellite. Earth sensors were either static, without moving parts, or scanning. Scanning was done by rotating the satellite, rotating a mirror with a motor, or rotating a mirror with a torsion bar. Most sensors operated in the infrared wavelengths because the radiation at those wavelengths was more uniform than that in the visible bands and is unaffected by eclipses. Many CubeSats use static Earth sensors because they are simple, compact, and inexpensive. A wide variety of models are available.