| Abstract: | The primary objective of this research is to provide an analytical solution to the problem of optimizing the design of manned spacecraft systems with respect to the modular level at which on-board replacement of failed modules should be carried out. Failed modules are assumed to be non-repairable. The optimum design is considered as a system with the minimum weight, consistent with mission requirements, for which a required reliability can be attained. A specific set of design alternatives in the form of a hierarchy of candidate replacement modules is used as the framework from which an optimum design is selected. The reliability expressions for spared systems are derived under the assumption that the components follow a negative exponential failure distribution. A detailed derivation of the reliability of a series-parallel system with spares is presented, and comparisons are made with a series spared system. The effect of having common components is spared systems is discussed and illustrated in graphs for specific cases. An advantage of increasing component weight to achieve commonality of components is demonstrated. ... |
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