The committee concludes that system efficiency concepts in the BR must focus on risks of adverse crew health events associated with technology and system failures.

Recommendation 4.4

The committee recommends that the current definition of risk be altered to clearly identify at least two types of risks: (1) health and medical risk, defined as the conditional probability of an adverse event to the human system (i.e., crew health or medical event) resulting from exposure to the space flight environment, and (2) engineering technology and system performance risk, defined as the conditional probability of an adverse event resulting from the space flight supersystem that affects crew health or mission success.

THE CASE OF ADVANCED HUMAN LIFE SUPPORT

The engineering and system technology risks found in the advanced human life support category are linked clearly to human health risks. Advanced human life support comprises food and life support systems, environmental monitoring and control systems, and EVA technologies and the human factors related to these technologies. In the area of Advanced Human Support Technologies, NASA faces challenges that may be divided into two areas: (1) determination of the optimal technology and (2) engineering development and qualification of the hardware, software, and operational procedures required to realize the system’s performance. Neither of these challenges is associated directly with crew health risks, except through the development of medical and toxicological requirements that advanced human life support technologies must meet. Notwithstanding the recommendation above (i.e., that the BR should be focused only on engineering technology and system performance risks related to the conditional probability of an adverse crew health or medical event resulting from the space flight supersystem), the committee provides some discussion here of the two challenges.

Determining the optimal technology involves interrelated studies of the medical and toxicological, physical, chemical, and biological sciences and to date has built on accumulated experience. In the context of long-duration missions, ensuring highly reliable performance of technologies will depend on two principal means of verification: stress testing and full-



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