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Model-based Diagnosis of a Satellite Electrical Power System woth RODON

As space exploration vehicles travel deeper into space, their distance to earth increases. The increased communication delays and ground personnel costs motivate a migration of the vehicle health management into space. A way to achieve this is to use a diagnosis system. A diagnosis system uses sensor readings to automatically detect faults and possibly locate the cause of it. The diagnosis system used in this thesis is a model-based reasoning tool called RODON developed by Uptime Solutions AB. RODON uses information of both nominal and faulty behavior of the target system mathematically formulated in a model. The advanced diagnostics and prognostics testbed (ADAPT) developed at the NASA Ames Research Center provides a stepping stone between pure research and deployment of diagnosis and prognosis systems in aerospace systems. The hardware of the testbed is an electrical power system (EPS) that represents the EPS of a space exploration vehicle. ADAPT consists of a controlled and monitored environment where faults can be injected into a system in a controlled manner and the performance of the diagnosis system carefully monitored. The main goal of the thesis project was to build a model of the ADAPT EPS that was used to diagnose the testbed and to generate decision trees (or trouble-shooting trees). The results from the diagnostic analysis were good and all injected faults that affected the actual function of the EPS were detected. All sensor faults were detected except faults in temperature sensors. A less detailed model would have isolated the correct faulty component(s) in the experiments. However, the goal was to create a detailed model that can detect more than the faults currently injected into ADAPT. The created model is stationary but a dynamic model would have been able to detect faults in temperature sensors. Based on the presented results, RODON is very well suited for stationary analysis of large systems with a mixture of continuous and discrete signals. It is possible to get very good results using RODON but in turn it requires an equally good model. A full analysis of the dynamic capabilities of RODON was never conducted in the thesis which is why no conclusions can be drawn for that case.

Olle Isaksson


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