A reusable state-based guidance, navigation and control architecture for planetary missions

JPL has embarked on the Mission Data System (MDS) project to produce a reusable, integrated flight and ground software architecture. This architecture will then be adapted by future JPL planetary projects to form the basis of their flight and ground software. The architecture is based on identifying the states of the system under consideration. States include aspects of the system that must be controlled to accomplish mission objectives, as well as aspects that are uncontrollable but must be known. The architecture identifies methods to measure, estimate, model, and control some of these states. Some states are controlled by goals, and the natural hierarchy of the system is employed by recursively elaborating goals until primitive control actions are reached. Fault tolerance emerges naturally from this architecture. Failures are detected as discrepancies between state and model-based predictions of state. Fault responses are handled either by re-elaboration of goals, or by failures of goals invoking re-elaboration at higher levels. Failure modes an modelled as possible behaviors of the system, with corresponding state estimation processes. Architectural patterns are defined for concepts such as states, goals, and measurements. Aspects of state are captured in a state-analysis database. UML is used to capture mission requirements as Use Cases and Scenarios. Application of the state-based concepts to specific states is also captured in UML, achieving architectural consistency by adapting base classes for all architectural patterns.