AUTOMATED-ANALYSIS OF PHASED-MISSION RELIABILITY

The methodology for automated analysis of phased missions is based on the solution of a discrete-state continuous-time Markov model. The phase-change times are deterministic. A method is presented for combining models for each phase into one model. This results in a model that can be substantially smaller than required by other methods. A unified framework is used for defining the separate phases using fault trees, and for constructing and solving the resulting Markov model. The usual solution technique is altered to account for the phased nature of the problem. The framework is described for a simple 3-component, 3-phase system that has appeared often in the literature. A hypothetical 2-phase mission is solved that involves the Fault Tolerant Parallel Processor under development at the C. S. Draper Laboratory. This approach is especially useful where several phases are repeated many times because each phase need to be described only once. This approach applies where the transition rates (failure and repair rates) are constant, and where the phase change times are deterministic. If any of these criteria are not met and if the system is not very large, then the approach proposed by Smotherman (1989) is appropriate.