An Event Tree/Fault Tree/Embedded Markov Model Approach for the PSAM-8 Benchmark Problem Concerning a Phased Mission Space Propulsion System (PSAM-0318)

The object of analysis of the proposed benchmark exercise is a system of ion propulsion for a science mission to the outer solar system. The propulsion system consists of a single propellant tank and 5 propulsion assemblies. The mission consists of 7 phases with different durations and requirements for the number of operational assemblies. The objective of the benchmark exercise is to determine the time dependent reliability of the propulsion system over the planned mission duration using the provided reliability data. Mission success implies success of all phases. The solution approach here undertaken uses fault-tree/event-trees (ET/FTs) for each functional mode (start up, shut down, operation and no-operation) to generate the transition probabilities of a discrete-time, inhomogeneous embedded Markov chain consisting of 11 states. Results of the study show that assembly failure during Start Up and the Shut Down functional modes of the propulsion system significantly contribute to mission failure.