Proceedings of the Eighth International Conference on Probabilistic Safety Assessment & Management (PSAM)
Aerospace: Phased Mission Analysis II
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In this paper, a direct Monte Carlo simulation method is proposed for estimating the time-dependent reliability of a space propulsion system within its mission. The system consists of five thruster assemblies and a single propellant supply. Each assembly has one propulsion power unit and two ion engines, one of which in standby mode. The mission is divided in seven phases, which from the point of view of the Monte Carlo simulation of the individual assemblies can be collapsed into four, each one consisting of an initial operating time followed by a standby period until the start of the next phase.
The complexity of the problem stems from the startup, operation and shutdown logic of the assemblies, of which two are required in the first phase and three in the following ones. Failure of an assembly causes it to be replaced by the first available in standby.
Furthermore, propellant leakage events leading to system failure may occur to some components. These occurrences are found to be largely dominant with respect to loss of system reliability so that an analysis of their effects is carried out.
Finally, common cause failures are considered, limited to groups of two to five components among the propulsion units, ion engines and fuel line valves of all assemblies.