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Completed TRL 4 (started at 2, targeting 4)
Thermodynamic vent systems (TVS) have been explored to aid in pressure control and to reduce boiloff losses in cryogenic propellant tanks for spacecraft. A traditional TVS utilizes an active pump to pull propellant from the storage tank, run it thorough an external heat exchanger where it is cooled by evaporating some percentage at a lower pressure, and then reintroducing it back into the vessel. The proposed passive TVS eliminates all external hardware and active pumps by placing the heat exchanger and valves inside the propellant tank. Cooling is still achieved by sacrificing a percentage of the propellent to low pressure (i.e. vacuum), but instead of evaporation, refrigeration is achieved by desorption from a nano-porous media integrated into the TVS heat exchanger. This cooling effect is non-localized (i.e. it can be distributed over the entire heat exchanger surface) and requires only two valves to operate. The proposed project will design, build and test a lab scale prototype passive TVS using liquid nitrogen as the cryogenic propellant.
Overall heat load on the cryogenic vessel is greatly reduced with a PTVS, which further decreases the propellant loss due to boil-off. Overall system complexity and mass may be substantially reduced as well versus traditional TVS setups; and the PTVS is likely better-suited to zero-g environments because it is less sensitive to issues related to liquid positioning and settling inside the tank.
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