Zero-g Hydrogen Tank Venting Systems

A cryogenic propellant tank in space absorbs heat, resulting in a tank pressure rise even with a heavy thermal-protection system. Vapor venting to relieve tank pressure can be accomplished easily on the earth’s surface or during powered flight because the liquid and vapor occupy predictable positions within the tank and a simple vent pipe can be employed; however, under low-gravity conditions the vapor/liquid distribution in the tank can shift easily as the result of small disturbing forces. Settling rockets have been used to orient the liquid and vapor in present-day venting applications, but these affect vehicle guidance and are excessively heavy for any but very low acceleration levels and settling times. It is important, therefore, to develop more efficient methods for venting vapor.