Multiple Loop Heat Pipe Radiator for Variable Heat Rejection in Future Spacecraft

As NASA refocuses its human mission ambitions to colder areas of exploration beyond Low Earth Orbit, the need for improved variable heat rejection thermal control systems increases. To account for large variations in heat loads and environment temperatures, a thermal control system with a large turndown ratio is required. This paper presents a variable heat rejection system that uses multiple Loop Heat Pipes (LHPs) to reject large heat loads from a single-phase pumped loop, with high turndown ratios. A novel method of LHP control through local flow rate modulation of the single-phase fluid is developed and demonstrated. Systematic Thermal Desktop modeling of multiple LHP systems was performed to demonstrate the potential of this method. A modeled 2.5 kW three LHP system was shown to have a turndown ratio of 10:1 at a sink temperature of -41°C K and a turndown of 1.5:1 at a sink temperature of -269°C. Finally, an experimental study of a two-LHP system was performed to support the conclusions of the modeling effort.