Quantitative risk analysis support to decision-making for new systems

Nowadays, it is widely accepted that scenario-based probabilistic risk assessment (PRA) is needed to support key decisions about new space flight systems. However, taking a risk estimate at face value and comparing it with a management “threshold” to determine whether a system is safe enough is too simplistic. This paper discusses considerations that need to accompany PRA results in particular decision contexts. The present point is not to criticize PRA itself; others have eloquently stressed the point that, for complex, high-stakes systems, whatever PRA's imperfections, doing PRA is better than not doing it. But while all analysis results are hostage to underlying assumptions, this is especially true for PRA, and over the years, PRA results have occasionally been overinterpreted or otherwise misused. In short, there are more enlightened and less enlightened ways to understand and use PRA results. This paper discusses several issues relating to these concerns, and suggests ways of dealing with them.