A Steam Engine for the Space Age: Thermodynamic Analysis of a Detonation Thruster With Water Electrolysis Propellant Generation

A thermodynamic model of a water electrolysis system is developed and integrated into a thermodynamic system model of a detonative combustion engine to enable the analysis of theoretical small-spacecraft detonation propulsion systems using water electrolysis for propellant generation. Due to the additional time required to generate propellants via electrolysis, these thrusters lend themselves well to infrequent, impulsive firings rather than sustained burns. Performance characteristics including specific impulse, energy efficiency, and a theoretical maximum impulse are identified for a representative nanosatellite-class spacecraft thruster with ideal and nonideal detonation combustion operation using an annular combustor with a plug nozzle and compared to deflagration operation using a traditional converging-diverging nozzle. The volume savings from stored liquid water propellant are also quantified compared to compressed gas tanks with equivalent thruster performance, with some configurations representing a volume reduction of multiple orders of magnitude. Results suggest that the in-space detonation thruster architectures characterized in this analysis are potentially attractive for applications such as station-keeping or orbital transfers.