Modeling process risk contributions for the Space Shuttle Probabilistic Risk Assessment (PRA)

The processes that are the focus of this paper are the processes that are carried out between missions on the Space Shuttle. These processes are the manufacturing processes, fabrication processes, assembly processes, testing processes, maintenance processes, and inspection processes that are carried out from one Space Shuttle landing to the next Space Shuttle launch. We present approaches for explicitly modeling these process contributions in accident scenarios that can be used in the Space Shuttle Probabilistic Risk Assessment (PRA). Explicitly modeling process contributions is important since their risk contributions can then be explicitly calculated and can be prioritized. To demonstrate the utility of the techniques that are presented, we illustrate an accident model for hydrazine fires occurring in the Auxiliary Power Unit (APU) of the Solid Rocket Booster (SRB) for the Space Shuttle.