Development of a Dynamic Response Model Considering Trapped Gas Effect for Spacecraft Liquid Propulsion Systems

Abstract

In the liquid propulsion system for a spacecraft, a dynamic behavior, such as pressure fluctuation caused by valve operation, can change significantly because of gas bubbles that become trapped in pressure conduits or pipe joints. This study has developed a dynamic response model that considers the trapped gas effect to improve the system-level integrated model of a spacecraft liquid propulsion system. The trapped gas effect in the proposed model is expressed as a volume change of gas phase remaining in a branch pipe by the equation of state for a real gas and the energy balance equation based on a gas-liquid accumulator model. The proposed model can reproduce effects caused by gas volume changes due to pressure wave fluctuation and reflection. A fundamental test was conducted in a simplified single-pipe system of a spacecraft propulsion system to validate the proposed model. The test confirmed that the proposed model could reproduce the peak frequency of the pressure history with a relative error of less than 7 % and the water hammer surge pressure with a relative error of less than 9 %.