occur in space. Furthermore, the committee suggests that the tumor studies should be coupled with appropriate mechanistic investigations to provide an understanding of the underlying carcinogenic processes.

Probabilistic Risk Assessment

The committee notes that the risk projections discussed in NASA’s proposed space radiation cancer risk assessment model and uncertainties are not presented or intended as being based on a probabilistic risk assessment (PRA) approach. NASA’s proposed model is a health-effects model intended to provide estimates of cancer risk and uncertainties for defined space radiation exposure scenarios. More generally, however, the cancer risk to astronauts is dependent on much more than a defined scenario model of health effects, with engineered barriers, in the space radiation environment. Experience with full-scope PRAs of complex systems indicates the importance of accounting for the “what can go wrong during actual operations” scenarios, as such scenarios generally drive the overall risk. Thus, the committee suggests that comprehensive, mission-specific PRAs also be considered so as to enable accountability for the “what can go wrong” scenarios in the overall risk projections.


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