| Launch vehicle history was assessed for mission success, together with the influence of vehicle and mission attributes on that history. The information set comprised eleven launch vehicle families, and fifty different stages or stage families which were used in various combinations to make up various vehicle models. The total number of models is sixty five and ranged from one for Shuttle to twenty three for Thor/Delta. Relatively few failures were design mode failures subject to reliability versus capability analysis. More prevalent were unrecognized mode failures associated with lack of knowledge, human errors, or unrecognized variations in critical parameters. Since unrecognized mode failures are not subject to explicit evaluation, historical data is necessary to address failure occurrence frequency and the influence of design and process attributes on the frequency.; A technique for Launch Vehicle Reliability modeling, based on flight mission process description in terms of states and phases, is defined. The phase transition probabilities define the probability of proceeding along the path states to mission success, or the probability of transitioning to a failure state. These phase transition probabilities are elements of a Markov process so that the probabilities of mission success or failure can be found from the resulting multistep transition probability matrix. The vehicle phase transition probabilities are developed in terms of the union of failure probabilities for the stage transportation functions operating during that phase, and then the stage phase function failure probabilities are related to the underlying failure causes.; The methodology provides a framework to relate design attributes to failure probability estimates and to update the estimates as the detailed design and analysis warrant. A failure probability estimating relationship, consistent with this methodology, was developed and the parameters of the relationship were estimated based upon the mission outcomes observed in the historical data sample. This methodology and failure probability estimating relationship provides a benchmark and a consistent framework for that benchmark, for evaluation and comparative evaluation of launch vehicle mission failure probability.; Although this effort focused on launch success or mission completion reliability, the methods that resulted are capable of extension to the other important reliability measures. |
