HIPPARCOS precise attitude determination methods and mission results

The HIPPARCOS mission objectives require stringent attitude determination accuracy. This requirement is achieved by an on-board capability which is augmented by ground support during critical phases of the mission such as initialization of on-board attitude determination and following occultations. An important feature of the initialization procedure for on-board attitude determination is the method whereby star pattern recognition takes place on-ground. The observed positions of the stars thus identified are used to refine attitude estimates. Throughout normal operations ground support is required to uplink star position data and monitor on-board attitude estimation performance. This paper summarizes the overall design philosophy and the individual components which participate in the attitude determination. The results obtained during the mission to date are presented and discussed.