Shape Memory Alloy Torque Tube Based Thermosiphon for Passive Thermal Control

Spacecraft tailored for missions beyond low Earth orbit face difficult thermal control challenges. Lunar missions call for systems that can survive the extreme surface temperature differences between the lunar day (400K) and night (140K), meaning the thermal control system may need to reject higher operational heat loads to warm environments during the lunar day when systems are in use and lower heat loads to cold environments during sub-system hibernation at night. Shape Memory Alloy (SMA) torque tube-based thermosiphons allow conventional flat plate radiators to be autonomously rotated from a full view of space to a limited view of space based on the temperature of the SMA torque tube alone. The SMA tube is an essential component enabling a compact vapor cycle, harnessing the temperature contrast between hot and cold regions of the system to act as a heat pump driven by the vaporization and condensation of a working fluid. The torque tube takes its austenitic twist angle when the fluid is hot, orienting the radiator panel to maximize its view to space therefore maximizing heat rejection; it takes its trained martensitic twist angle when the fluid is cold, orienting the panels to minimize heat rejection. This work considers development of a computational model created to integrate the thermal, mechanical, and advective components of the SMA torque tube thermosiphon system. This model is used to evaluate the thermal regulation of a fuel cell system operating in a lunar setting. Progress on hardware demonstrators will also be reviewed.