Study of fluid loop systems for use in spacecraft thermal control

A study has been carried out of an active thermal control system for spacecraft which consists of a fluid loop that connects a heat source with a heat sink. Heat transport from source to sink is achieved by forced convection with a coolant circulating in the loop. Three fluid loop systems have been defined based on different heat sinks: a standard counterflow liquid/liquid heat exchanger, a liquid/air crossflow multi-pass heat exchanger, and a space radiator. It is shown that, for a given heat transport rate, there must exist a minimum positive difference between source and sink temperatures. In the case of smaller or negative temperature differences a heat pump must be incorporated in the loop. It is estimated that fluid loop systems without heat pumps designed for heat transport rates of up to a few kW will have a mass of approximately 10 kg. The power requirement of a heat pump depends strongly on the difference between source and sink temperatures and is approximately proportional to the heat transport rate.