for water purification aboard Mir. (The problem was solved subsequently by installing an anion exchange resin filter at the water tap, but only after several years of thyroid abnormalities among flight crews.)

Other potential interactions appear in the BR. For example, many of the problems listed under Risk 25 (human performance failure due to neurobehavioral problems) are the result of problems listed under Risk 24 (human performance failure due to poor psychosocial adaptation (NRC, 1998; IOM, 2001). The poor coping skills of one crew member may result in reduced work productivity, leading to increased tension and conflict within the crew and resulting in reduced sleep and increased symptoms of depression, anxiety, and anger among all crew members (Palinkas, 1992, 2003). Whereas some of these potential interactions are identified in Appendix B of the BR, that appendix is not referenced in the body of the text and the current version of the BR does not adequately emphasize these interrelations and their implications for countermeasure development, risk management, and risk mitigation.

Recommendation 2.2

The committee recommends that greater effort be devoted to identifying and explaining the interrelations among risks and risk mitigations that are grouped within and across the cross-cutting categories in the BR.

Status of Readiness Levels

In general, the probability of an adverse event can be reduced in two ways: (1) by eliminating the risky procedure or activity or (2) through mitigation strategies and approaches that reduce the probability of adverse events to acceptable levels. Because space flight, in particular the exploration class missions, carries inherent risks, the BR emphasizes the latter approach through the development and application of countermeasures.

A variety of deliverable products result from the BR; they enable desirable outcomes or solutions to answer research and technology questions and reduce risk to support the human system in space. Progress in these areas is gauged by establishing “readiness levels” that delineate the level of maturity of countermeasures or technologies (Countermeasure Readiness Level [CRL] and Technology Readiness Level [TRL], Table 2-1). The process emulates safety improvement programs (U.S. Department of Trans-

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