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Managing Space Radiation Risk in the New Era of Space Exploration
Recommendation 2-1. Planning for long-term changes in space climate. NASA must ultimately judge how much weight to assign to the cautionary findings from ice cores on a potentially more severe space radiation climate in the future. Given that the Exploration initiative envisions a commitment of the nation’s resources that spans decades, NASA should ensure that the mission architecture has sufficient flexibility and margin to cope with such changes, should they occur.
Finding 2-5. The King spectrum as a design standard. Although the committee recognizes the advantages of adopting a specific solar proton spectrum as the design standard, NASA’s current strategy of evaluating the efficacy of an SPE shielding configuration using only the August 1972 King spectrum is not adequate. Under typical depths of shielding for Exploration vehicles, the level of radiation exposure produced by other large events in the historical record could exceed the exposure of August 1972.
Finding 2-6. Spectra data fitting. There is no theoretical basis for any of the published spectral fits to large SPEs. The extrapolation to energies beyond 100 MeV must therefore be guided by data. Solar proton spectral forms based on data that do not extend to ~500 MeV may very well give misleading results in evaluations of the efficacy of radiation shielding for astronauts.
Recommendation 2-2. SPE design standards. The dose levels made possible by a shielding design should also be calculated using the observed proton spectrum from other large events in the historical record, even if it is not feasible to modify the shielding design as a result. The October 1989 event is particularly important in this regard.
Recommendation 2-3. Uncertainties in spectra data fitting. NASA should make use of existing data to reevaluate the spectra beyond 100 MeV in large events in the historical record and should assess the impact of uncertainties in the high-energy spectra on the adequacy of radiation shielding designs.
Finding 2-7. Knowledge of radiation from nuclear ground power. Experience with nuclear power on Earth has provided sufficient knowledge to create this capability on the Moon. The remaining challenges are engineering problems, not scientific problems. Experiments to show the operational safety of space and planetary-surface fission power systems, including unique design features such as compactness, light weight, and heat transport and heat rejection in reduced gravity, will be important.
Finding 3-1. Uncertainty in radiation biology. Lack of knowledge about the biological effects of and responses to space radiation is the single most important factor limiting the prediction of radiation risk associated with human space exploration.
Finding 3-2. Funding cuts to radiation biology research. NASA’s space radiation biology research has been compromised by the recent cuts in funding, particularly in research addressing noncancer effects.
Finding 4-1. State of radiation protection plans for lunar missions. The use of surface habitat and spacecraft structure and components, provisions for emergency radiation shelters, implementation of active and passive dosimetry, the scheduling of EVA operations, and proper consideration of the ALARA principle are strategies that are currently being considered for the Constellation program. These strategies, if implemented, are adequate for meeting the radiation protection requirements for short-term lunar missions.
Recommendation 4-1. Strategic design of Orion. As the design of Orion continues to evolve, designers should continue to consider and implement radiation protection strategies.
Finding 4-2. State of radiation protection plans for Mars missions. For longer-duration lunar and Mars missions the currently large uncertainties in radiological risk predictions could be reduced by future research. Without such research, it may be necessary to baseline large shielding masses and reduced-length missions, and/or delay human