Onboard attitude determination for a small satellite

A system for attitude and rate estimation for a small satellite is described. The estimates are used for onboard attitude control and the precision requirements are limited. An important feature of the effort is, however, the ability of the system to handle multiple sensor faults. Presented are results from the Danish Ørsted micro satellite. Attitude estimation on Ørsted is based on a gyroless configuration with a star camera as the primary attitude instrument. Sun sensor and magnetometer data is processed in a Kalman filter to provide estimates independently of the star camera. The combined systems make it possible to maintain adequate attitude information through all mission phases and in situations with sensor malfunction or temporary blackout. Filter-strategies are presented with focus on the Kalman filter processing and expected performance is demonstrated through simulations.