Long-term storage of cryogenic propellants in space has been investigated for the Earth Departure Stage (EDS) proposed by EADS Astrium as a part of exploration space transportation architecture study initiated by the European Space Agency (ESA). In a typical mission, a 23-ton EDS including 16.7 tonnes of propellant is expected to remain in Low Earth Orbit for up to 30 days. The past flights have shown that during orbital coasting, a typical cryogenic upper stage experiences propellant boil-off of 2% of the original propellant mass per day. For the EDS mission, such high boil-off would be prohibitive.The goal of this research is to investigate performance limits of passive thermal protection system (TPS) in reducing the EDS propellant boil-off. A coupled thermal model based on ThermXL software has been developed to solve steady state and transient cases. Additional models have been developed for structural sizing, and for heat transfer in liquid-hydrogen (LH2) and liquid-oxygen (LOX). The models were used to analyze different passive TPS options, structural interfaces, and tank designs. A 23-ton EDS and a 30-day mission has been used as a baseline for the research. The analysis also addressed 50-ton and 24-ton variants of EDS, introduced by ESA in January 2009. For each TPS concept the propellant boil-off mass and TPS dry mass were calculated. The analysis showed that improved passive TPS design can reduce the average daily boil-off to 0.015%.
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