Low-Temperature Thermal Control for a Lunar Base 901242
The lunar environment places some unique demands on a thermal management system designed for manned lunar missions. A principal concern is that for many prime base locations the effective thermal sink temperature is often near or above nominal room temperature (25°C). This is due to the fact that a conventional radiator must look at either, or both, the sun and the hot lunar surface. Direct rejection of waste heat at such temperatures is thus impossible, and some alternative approach is needed to enable a sustained mission. This paper presents three such alternative systems: a heat pump assisted central thermal bus; an innovative, selective field-of-view radiator; and use of the lunar regolith as a heat sink. All of these concepts appear feasible, but each has uncertainties associated with its practicality and weight estimate. The heat pump assisted thermal bus appears to be the most viable concept and is discussed herein in some detail. Alternative heat pump system configurations are described and evaluated. These include 1) modular heat pumps connected to a central, high-temperature thermal bus which is then connected to the radiators, 2) a Space Station Freedom-type, two-phase thermal bus connected directly to the loads and then connected, via large central heat pumps, to the radiators, and 3) a central heat pump system similar to 2) but with two independent loops set to different saturation temperatures. These three alternative heat pump system concepts are compared on a weight basis against the selective radiator and regolith concepts. Using realistic weight and thermal sink assumptions, and including a weight penalty for heat pump compressor power, the specific weights for each system type are 1) 149 kg/kW for modular heat pumps, 2) 133 kg/kW for central heat pumps 3) 134 kg/kW for the dual loop heat pump concept, 4) 95 kg/kW for the selective field-of-view radiator, and 5) 126 kg/kW for the regolith concept. These results are all sensitive to effective sink temperature, which is, in turn, dependent upon the assumed level of radiator degradation due to environmental factors such as solar wind, UV radiation, and especially, dust contamination from surface operations.