We present a dynamic fault tree model of the benchmark propulsion system, and solve it using Galileo. Dynamic fault trees (DFT) extend traditional static fault trees with special gates to model spares and other sequence dependencies. Galileo solves DFT models using a judicious combination of automatically generated Markov and Binary Decision Diagram models. Galileo easily handles the complexities exhibited by the benchmark problem. In particular, Galileo is designed to model phased mission systems. A phased mission system (PMS) is defined as a system whose mission is composed of multiple, consecutive and non-overlapping phases. Generally, the system configuration, failure criteria and component behavior of different phases may be different. Because the system can change configuration and behavior from phase to phase, dependencies arise between the variables representing components in different phases. The Galileo approach to phased-mission system handles phased mission dependencies as well as dependencies arising from common cause failures, complex redundancy management, shared and cold spares, and other functional dependencies. Galileo is a software tool for dynamic fault tree developed by the University of Virginia under contract to NASA. Galileo is available commercially from Exelix (exelix.com).
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