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The optimum radiator configuration in hot lunar thermal environments is one in which the radiator is parallel to the ground and has no view to the hot lunar surface. However, typical spacecraft configurations have limited real estate available for top-mounted radiators, resulting in a desire to use the spacecraft's vertically oriented sides. Vertically oriented, flat panel radiators will have a large view factor to the lunar surface, and thus will be subjected to significant incident lunar infrared heat. Consequently, radiator fluid temperatures will need to exceed ~325 K (assuming standard spacecraft radiator optical properties) in order to provide positive heat rejection at lunar noon. Such temperatures are too high for crewed spacecraft applications in which a heat pump is to be avoided.

With new direction to return to the Moon, NASA is developing highly efficient and lightweight extravehicular activity (EVA) equipment for working on the rugged lunar terrain. This paper presents results and evaluations of lunar thermal environments and design challenges for the EVA system. The evaluations include a review of basic lunar environment data, a review of metabolic rate predictions, analyses and reviews of spacesuit heat leak effects in past designs, and methods to improve the performance of spacesuit-mounted radiators in a hot lunar environment. In addition to reviewing existing lunar thermal environment data, a simplified thermal model is presented that can simulate the lunar surface temperature variation as a function of latitude and time on the lunar surface. The assumed physical and optical properties of the lunar soil as well as the solar heating on the Earth's Moon are also presented.