Abstract: A method for operating self-pressurizing propellants in space thruster chambers and nozzles heated by resistive, radiative or nuclear methods at temperatures hundreds of degrees above the decomposition temperature. The method is defined by reducing the chamber volume Vc and increasing the nozzle throat area A* such that a propellant vapor with sonic velocity a* experiences a high temperature residence time that is less than 10 milliseconds. In other aspects of the invention propellant vapor is formed from a self-pressurizing propellant and the residence time is such that the propellant vapor does not decompose nor does the propellant vapor polymerize to a solid.