Spacecraft Fault Detection & Isolation System Design Using Decentralized Analytical Redundancy

Fault detection and isolation (FDI) functionality constitutes a critical element of spacecraft fault protection system capabilities. The FDI schemes currently implemented on board operational spacecraft suffer from a lack of systematic design methods and resulting behavior. While model based diagnosis techniques can resolve a number of these issues, their applicability to spacecraft has been limited until now largely due to an unfavorable net value proposition. An approach integrating analytical redundancy based diagnosis into a conventional spacecraft FPS architecture is presented. The approach is based on a novel decentralized diagnosis architecture based on analytical redundancy relations. A systematic approach to designing such decentralized model based diagnosers for spacecraft is discussed, with a focus on the attitude and orbit control system. Analytical redundancy relation based error monitors and activation rules relying on the corresponding fault signatures are derived during the design phase. A comparison with the diagnosis functionality as currently implemented in the Cassini attitude and articulation control system fault protection is presented in terms of the design & development effort. It is demonstrated that the presented diagnoser design approach addresses several issues with the conventional methods, while having reasonable additional costs