Development of Flight Demonstration Hot Reservoir Variable Conductance Heat Pipes for Microgravity Testing and Future Lunar Landers and Surface Systems

The lunar landers and rovers require a reliable tight passive thermal control technology due to their exposure to the ambient's harsh temperature conditions such as the lunar night where the temperature drops to about -280?F (-173.3?C) and lasts for a continuous 14-day period. Advanced Cooling Technologies Inc. (ACT) has devised and demonstrated a hot reservoir variable conductance heat pipe (HR-VCHP) to be an ideal passive variable thermal link between the payloads and the radiator for such lunar landers since HR-VCHP can offer much tighter thermal control capability when compared to a regular cold-biased reservoir VCHP. Under NASA Small Business Technology Transfer (STTR) program, ACT and Case Western Reserve University (CWRU) further matured this technology by introducing a novel fluid management feature that enables a non-condensable gas (NCG) flow to generate inside the device. This flow can maintain the moisture level of the reservoir and lead to more reliable VCHP operation in space. Two flight demonstration units (FDU) of HR-VCHPs with NCG flow are under development: one for microgravity testing on International Space Station (ISS) and another one for lunar lander thermal control applications. The FDU for microgravity testing is made from copper where the working fluid is water while the HR-VCHP for the future lunar landers is made from aluminum where the working fluid is ammonia or propylene. This paper will present a compact HR-VCHP prototype description, reliability testing results, and the development status of two FDUs.