Space-based Human Reliability Analysis Development, Year 2 (HRA)

For all human space programs, NASA currently has safety requirements for probability of Loss of Crew (LOC) and Loss of Mission (LOM). NASA uses Probabilistic Risk Assessments (PRAs) to assess and verify these probabilistic requirements. These PRAs take into account all known risk contributors and their interactions, such as how the crew, software, and hardware work together to achieve mission objectives in the environment being flown. Human Reliability Analysis (HRA) assesses the human contribution to risk in PRAs. Current HRA techniques were developed for ground applications, primarily for commercial nuclear power plant control rooms using Earth- (or ground-) based human reliability data to estimate human error probability (HEP). These ground-based HRA techniques were assumed a reasonable tool for short-duration space missions by the Johnson Space Center (JSC) Safety & Mission Assurance (SMA) Analysis Branch (NC4) in the late 1990’s, such as Space Shuttle missions. However, it is important to account for the impacts the space environment may have on human health and performance (HH&P). As mission durations grow and humans travel beyond Earth orbit, human performance will be impacted. Current indications show higher risk due to fatigue, physiological effects due to extended low gravity environments, and others, which may impact the crew’s cognitive abilities, as well as their physiology, and yield a higher probability for LOC and LOM than current HRA techniques produce. Therefore, NASA has a need to extend current ground-based HRA techniques to a more space-based approach to more effectively predict the risk, both qualitatively and quantitatively, associated with human actions on space missions. By doing so, the agency will be able to focus resources on more appropriate risk drivers, such as specific training, conditioning, procedures, exercising, spacecraft displays and controls, etc. for these future missions. This study represents a follow-up to the 2014 review of HH&P directorate studies in-work. That study reduced the ~200 potential Performance Shaping Factors (PSFs) being studied by HH&P down to 35, which are more representative as candidates to a space-based HRA approach. Due to limit data available from HH&P, only publicly available “fatigue” data was applied to the Cognitive Reliability Error Analysis Method (CREAM) HRA approach currently used by JSC SMA in estimating human space program probability of LOC risk. Although the fatigue data was from the public domain and from ground based studies, it provides a first step toward modifying CREAM for space-based missions (i.e. SCREAM). The resulting change in HRA results showed a factor of 1.7 increase in the HEP from ground-based to space-based given end of mission human actions after 14 days.