Abstract
Fault tolerance of Spacecraft Attitude and Control Subsystem (AOCS) is extremely important because an AOCS failure can result in the total loss of spacecraft. More specifically, FDIR (Fault Detection, Isolation and Recovery) function has been applied to many satellites resulting in successful mission operations. This paper presents the FDIR function for the AOCS of ADEOS-II with emphasis on a newly developed FDIR for hybrid navigation. Hybrid navigation which is ADEOS-II nominal operational mode processes GPS Receiver (GPSR), Fine Sun Sensor Head (FSSH), Inertial Reference Unit (IRU) and Earth Sensor Assembly (ESA) for attitude determination and achieves specified attitude control accuracy. Regarding fault tolerance of hybrid navigation, by employing FDIR system, the automatic recovery from failure modes has been proven in the real orbit operations, and the highly robust AOCS was developed. Features of new FDIR are shown below. (a)The FDIR not only monitors anomalies of AOCS components but evaluate the attitude determination of hybrid navigation in comparison with the attitude determination of normal navigation operates independently. (b)The FDIR in case of anomaly turns into the normal navigation mode and maintains continuity of almost earth observation mission. The approach and algorithm developed in this FDIR design can be applied to next earth observing satellite required the precise attitude control accuracy.
