Safe May Not Be an Option, but Risk Mitigation Is

The Space Station program convened a Mishap Investigation Board (MIB) to investigate a High Visibility Close Call which occurred during US Extravehicular Activity (EVA) 23 on July 16, 2013. The MIB established the specific cause for the potentially catastrophic water leakage inside the Extravehicular Mobility Unit (EMU), which was a clog inside the EMU Fan Pump Separator, caused by inorganic material that led to water spilling into the vent loop. Additionally, the MIB identified Root Causes as any of the multiple factors (events or conditions, that are organizational factors) that contributed to or created the proximate cause and subsequent undesired outcome. Root causes are ones that if eliminated or significantly modified, would have prevented the undesired outcome. Trouble-shooting also identified a catastrophic failure mode previously unknown to the ISS program. The lessons learned resulted in 49 separate recommendations to the ISS Program to correct these issues that led to this incident and prevent future such mishaps. Many of these recommendations were being implemented before the report was complete, and all of them are being specifically addressed by the ISS Program. Additional insights from NASA astronaut and EVA 23 spacewalker Christopher Cassidy are included to provide additional insight to the incident and the resulting lessons learned.