Abstract: A method and system for delivering pressurized propellants to a rocket engine, that has significant advantages over the current state-of-the-art. One of the propellants, the "pressurizing propellant", is at least partially vaporized and the vapor is in pressure communicating relationship with other propellants on board the rocket-propelled vehicle. This vapor pressure pressurizes the propellants to a sufficient degree that they can be charged directly to the rocket engine, or the pressure may be boosted through pumps, if required. Moreover, the pressurized vapor may be used in other applications on board the vehicle, such as orbital adjustment, attitude control, station keeping, and the like. In several embodiments, the propellants are contained in variable volume reservoirs, exemplified by bladders and diaphragms. These variable volume reservoirs are preferably not subjected to tensile stresses when expanded, and are preferably designed for controlled volume reduction, when being drained of propellant.

Abstract: One of the propellants used in a bipropellant rocket engine has a vapor pressure sufficiently high under prevailing condition to generate vapor at a pressure sufficiently high to pressurize both the volatile component and the second rocket propellant and provide substantially the sole means for forcing the two rocket propellants from their storage to the rocket engine. In the preferred arrangement, both the components will be stored within the same pressure vessel, one preferably being contained within an expandable/collapsible bladder.