The Space Shuttle probabilistic risk assessment framework A structured multiphase multi-layer modeling approach for large and complex engineered systems

This paper introduces a unique modeling framework for developing PRA of large and complex-engineered systems, such as used in the current Space Shuttle PRA at NASA. With an overview of the specific methodology and techniques employed in the Space Shuttle PRA modeling process, the paper further describes a structured multi-phase and multi-level modeling approach (SMM), which is utilized to treat the overwhelming complexities of logic structure as well as the logistics of model development, integration and quantification processes. It is demonstrated that the SMM modeling technique can be used as a simple and efficient alternative approach for PRA modeling of extremely large and complex engineered systems. It should be noted that the examples shown are illustrative of the model features, but not necessarily of any detailed accident sequence produced by the space shuttle PRA (SPRA) study.