Passive Fuel Cell Surface Power System (PaCeSS)

NASA’s envisioned Lunar and Martian surface operations will require constant and reliable power systems. Traditional power architectures, including solar cells and batteries, cannot be solely relied upon due to the lengthy lunar nights and challenging thermal environments. How-ever, fuel cells, including primary fuel cells and regenerative fuel cells, represent a promising means for energy generation and storage on planetary and lunar surfaces. PaCeSS could further improve mission flexibility by significantly enhanc-ing reliability and longevity with fully passive fuel cell power generation capability. Test systems have been built to validate the performance characteristics of various PaCeSS technology elements, and many of the component materials have already been characterized. Some of these novel technology elements already demonstrated include a two-phase thermosyphon operation in fuel cell conditions, a passive shape memory actuator operation using two-phase water, and a shape memory alloy radiator turndown. Although the current design of the shape memory alloy actuated rad-iator system is dependent on partial gravity and space-like environments where heat rejection is performed primarily via radiation, there may be ways of using the same basic system for controlling fuel cell temper-ature via convective heat rejection for terrestrial applications. Addition-ally, other elements of this concept could be commercialized terrestri-ally, including the thermosyphon heat transport mechanism, a multi-purpose vapor chamber, and a thermal management system that uses water by-product as the thermal management medium. The Passive Fuel Cell Surface Power System is at a technology readiness level (TRL) 3 (analytical and experimental critical function and/or characteristic proof of concept) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale. NASA Johnson Space Center is developing a passive thermal management cooling system for a fuel cell. The cooling system uses a radiator comprising a shape memory alloy (SMA) actuator, and a thermosyphon-based system for heat transport that can eliminate the need of moving parts. Relying upon partial gravity for operation, the innovation, called “PaCeSS” for short, is highly promising for power generation and storage in lunar and planetary surface operations, and may be compelling for terrestrial industries interested in passive thermal management. Current fuel cells require active thermal management components such as pumps to push liquid coolant through a fuel cell stack and electronic control valves to operate radiator panels. These components have moving parts presenting several disadvantages: they limit the operational lifetime and reliability of a fuel cell system, and are a source of parasitic power draw because they consume energy from the fuel cell stack to power their operations. PaCeSS could eliminate the wear-and-tear of moving parts and reduce complexity associated with fuel cell system thermal management. It is a system-level solution that spans heat acquisition, heat transport, and heat rejection by incorporating a two-phase thermosyphon for passively removing heat from a fuel cell stack through a transport path. It then uses an SMA mechanism to actuate a radiator panel that can vary the heat rejection rate into space.