NASA's Space Suit: A Maintenance Study

Since the Space Shuttle retirement in 2011, the National Aeronautics and Space Administration (NASA) has lost its ability to provide comparable up and down mass to the International Space Station (ISS). One consequence of reduced mass exchange has been the extended operational life cycle of the Space Suit, known as the Extravehicular Mobility Unit (EMU), and extended periods between ground servicing. In 2013, NASA suffered a near-fatal release of water inside the EMU, leading a full review of the safety, reliability and maintenance practices of the EMU. NASA's mishap investigation board's final report determined that the water-in-the-helmet mishap was the unfortunate result of a series of extenuating events. This paper examines if these events are part of a wider trend of more frequent failures as a result of the extended maintenance cycle. EMU usage data is compared using both statistical hypothesis tests and reliability growth models to show that the incidence of failures for the current maintenance approach is not increasing over previous maintenance approaches. It is thus concluded that the mean time between failures of the EMU cannot be shown to change, but that the changing of the maintenance model due to the space shuttle retirement introduced high severity failure modes that were not adequately assessed due to a normalization of certain failures.