Optimization of Crew Shielding Requirement in Reactor-Powered Lunar Surface Missions

On the surface of the moon—and not only during heightened solar activities—the radiation environment is such that crew protection will be required for missions lasting in excess of six months. This study focuses on estimating the optimized crew shielding requirement for lunar surface missions with a nuclear option. Simple, transport-simulation based dose-depth relations of the three radiation sources (galactic, solar, and fission) are employed in a one-dimensional optimization scheme. The scheme is developed to estimate the total required mass of lunar regolith separating reactor from crew. The scheme was applied to both solar maximum and minimum conditions. It is shown that savings of up to 30% in regolith mass can be realized. It is argued, however, that inherent variation and uncertainty—mainly in lunar regolith attenuation properties in addition to the radiation quality factor—can easily defeat this and similar optimization schemes.