State Machine Fault Protection for Autonomous Proximity Operations
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Author(s)
Schulte, Peter Z.
Spencer, David A.
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Abstract
The capability to recover gracefully from hardware or software faults is critical for many aerospace applications. This is particularly true for missions involving proximity operations, where multiple vehicles are operating at close range. Previous proximity operations missions have experienced faults that resulted in a failure to meet mission objectives. Fault protection systems are used to detect, identify the location of, and recover from faults. Typically, aerospace systems use a rule-based paradigm for fault protection, where telemetry values are monitored against logical statements such as static upper and lower limits. The model-based paradigm allows more complex decision logic to be used. The state machine approach for model-based fault protection has been explored by industry but has not yet been widely adopted for aerospace applications.
This study focuses on fault protection for the Guidance, Navigation, and Control vehicle subsystem, which is essential for any aerospace vehicle and has many complex and interrelated hardware and software components. Two separate case studies have been analyzed through this work, one for atmospheric flight and one for space flight. The first case involves detecting hardware faults on an unmanned aerial vehicle used for aerial surveying and mapping and is addressed in a previous paper. The second case is the focus of this paper and involves automated proximity operations during approach and capture of the orbiting sample canister for a Mars Sample Return mission.
For each case study, high-level failure modes are identified and linked to individual root cause events via fault tree analysis. The results of the fault tree analyses are developed into a generic and modular state machine fault protection architecture. This architecture will apply to a wide variety of aerospace applications and contains components that can be rearranged, added, or removed easily. The architecture facilitates export of the state machine logic to flight software via autocoding or other methods.
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2017-09
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