The S-IVB also continued to thrust in a minimal amount by venting gaseous hydrogen, to keep propellants settled inside their tanks and prevent gaseous cavities from forming in propellant feed lines. This venting also maintained Safe and sound pressures as liquid hydrogen boiled off from the fuel tank. This https://lowpowersoc20863.madmouseblog.com/14537788/apollo-4-plus-can-be-fun-for-anyone