Introduction

Spacecraft thermal control techniques can be categorized as passive thermal control (PTC) or active thermal control (ATC). PTC can be achieved by control of conductive and radiative heat paths through selection of the proper geometrical configurations, insulation blankets, sun shields, radiating fins, surface thermooptical properties, thermal coatings, heat sinks, and phase-change materials. A PTC system does not involve moving parts or fluids. The spacecraft component temperatures are maintained within the desired range by proper control of the dissipated energy between all spacecraft elements through the conductive and radiative heat paths. However, to execute a design in which the PTC techniques cannot deal with environmental extremes or to accommodate equipment dissipating high power, employment of ATC techniques may be more efficient. In such cases, designs can be executed by the use of heaters, louvers, heat pipes, thermoelectric coolers, cryogenic coolers, and pumped fluid loops (PFLs).

PFLs are devices that provide efficient transfer of a large amount of thermal energy between two points by means of forced liquid convective cooling. PFLs for space applications are the subject of this chapter. A simplified PFL, as shown in Fig. 12.1, consists of a pumping device, a heat exchanger, and a space radiator. The cooling can be accomplished by the use of a coolant as the thermal energy transport agent. The coolant...