Active Thermal Control Systems for Lunar and Martian Exploration

Extended manned missions to the lunar and martian surfaces pose new challenges for active thermal control systems (ATCS's). Moderate-temperature heat rejection becomes a problem during the lunar day, when the effective sink temperature exceeds that of the heat-rejection system. The martian atmosphere poses unique problems for rejecting moderate-temperature waste heat because of the presence of carbon dioxide and dust. During a recent study, several ATCS options including heat pumps, radiator shading devices, and single-phase flow loops were considered. The ATCS chosen for both lunar and martian habitats consists of a heat pump integral with a nontoxic fluid acquisition and transport loop, and vertically oriented modular reflux-boiler radiators. The heat pump operates only during the lunar day. The lunar and martian transfer vehicles have an internal single-phase water-acquisition loop and an external two-phase ammonia rejection system with rotating inflatable radiators. The lunar and martian excursion vehicles incorporate internal single-phase water acquisition, which is connected via heat exchangers to external bodymounted single-phase radiators. A water evaporation system is used for the transfer vehicles during periods of high heating.