An oxygen-hydrogen pressurization system includes a cryogenic oxygen tank, cryogenic hydrogen tank, thermal switch, supercritical oxygen bottle, supercritical hydrogen bottle, and pressure management system and a thermodynamic vent system. The thermal switch permits heat to flow between hot and cool areas within the space vehicle to help facilitate pressure management within the cryogenic liquid oxygen tank and the cryogenic liquid hydrogen tank in conjunction with the higher pressure fluid from the supercritical oxygen tank and the fluid from the supercritical hydrogen tank and the added cooling from the pressure management system.