diation risks and risk mitigation. Further, the committee concurs with NASA’s assessment that the duration of the mission and the distance from Earth will determine the amount and type of radiation exposure and the required shielding for both the vehicle itself and the protective wear for EVA, with the associated weight and design implications. However, the conventional rule of thumb for terrestrial radiation protection (i.e., that protection against late radiation effects such as increased cancer risk will also protect against acute radiation effects) may not hold for HZE from GCRs, particularly with regard to CNS impairment. Therefore, the committee also concludes that NASA must conduct further research to clarify the extent to which protracted or low-dose HZE radiation exposure might contribute to mission-damaging CNS effects.

Recommendation 2.9

The committee recommends that a safe radiation exposure level be established by NASA for each relevant risk, based on projected flight duration and distance from Earth, and that the technology to keep the level of exposure below that limit be ensured. Inherent in this recommendation, and consistent with Recommendation 2.3, the committee concludes that NASA must conduct further research to clarify the extent to which protracted or low-dose HZE radiation exposure might contribute to mission-damaging CNS effects.

As with the other components of the BR, it will be essential to follow the developments in both biological research and shielding technology to ensure crew health and safety for longer-duration, higher-radiation-exposure exploratory missions.

Assessing the Sources and Impact of Long-Duration Space Flight on Crew Health and Incremental Risk

Crew performance can be compromised by (1) intrinsic health alterations that occur spontaneously due to natural processes in the space environment, (2) aspects of the space environment that impair health, and (3) inadequate or malfunctioning life support systems. Differences among the Design Reference Missions (ISS, Moon, and Mars), in terms of factors such as duration, amount of gravity, and type and extent of radiation exposure, are examples of how the mission itself will influence the interactions be-



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