Risk identification
The safety issue was identified while reviewing the Probabilistic Risk Assessment of a depressurization scenario in the telescope cavity. The failure scenario itself was previously known where a leak in the telescope cavity door seal sucks air out from the telescope cavity creating a negative pressure differential between the telescope cavity and the aft cavity. Two negative pressure relief valves were designed to handle this and other cavity negative pressure scenarios. However, the proposed new scenario had a leak area that was beyond the original design basis. Nevertheless, this failure scenario was deemed credible but with a lower probability of occurrence.