Abstract:

It is important to future human spaceflight programs, to understand the early mission risk and the impact of design, process, and operational changes on risk. The Shuttle risk progression assessment used the knowledge gained from 30 years of operational flights and the Shuttle Probabilistic Risk Assessment (PRA) to calculate the risk of Shuttle Loss of Crew at significant milestones beginning with the first flight. The results indicated that the Shuttle risk tends to follow a step function as opposed to following a traditional reliability growth pattern. In addition, the results showed that risk can increase due to trading safety margin for increased performance, due to external events or due to intended (disabling ejection seats) or unintended (Space Shuttle Main Engine Block II upgrade) consequences of design changes. This paper will focus on examining those cases where risk increased and explore the lessons that can be learned by new programs.