Shape Memory Alloys for Regulating TCS in Space (SMARTS): System Design and Thermal Vacuum Demonstration

NASA has identified variable-geometry radiators and thermal switches as a key technology in their 2020 Technology Taxonomy for enabling human exploration and operations. Variable-geometry radiators provide variable heat rejection capability, or turndown, to meet variable heat loads and environments, as might be experienced in a Lunar habitat or interplanetary vehicle carrying astronauts. Shape Memory Alloy (SMA) actuation offers lightweight, compact, and rugged methods for passive control of morphing radiators that vary geometry, providing turndown, in response to thermal stimuli. Additionally, SMA actuators used to passively activate thermal switches to control conduction paths produce more work output per unit mass than conventional actuators (exceeding an order of magnitude) and other active material actuators, including piezoelectric and paraffin wax actuators. SMAs for Regulating thermal control systems (TCS) in Space, or SMARTS, is an SMA enabled radiator system with thermal switch for adverse heating protection. SMA wires are conductively coupled to coolant passages, providing thermally responsive actuation to open and close the radiator at design temperatures to passively vary heat rejection, ensuring stable coolant outlet temperatures. SMA actuators, conductively coupled to the radiator, respond to adverse heating on the radiator panels by breaking thermal contact between the panel and the coolant passages at design temperatures. SMARTS has been built at a prototype system level and demonstrated in a relevant TVAC environment. Heat rejection comparable to flat panel radiators was demonstrated with the additional benefits of greater turndown than the NASA roadmap target of 6:1 and passive protection to adverse heating conditions. This work demonstrates design and analysis methods employed to tune SMA transition temperatures and predict response to thermal and mechanical loads. Upon project completion, the SMARTS technology is anticipated to be at a technology readiness level (TRL) 6, ready for implementation on upcoming Lunar missions.