Transient simulation of a differential piston warm gas self-pressurization system for liquid attitude and divert propulsion system

In order to obtain the dynamic characteristics of a differential piston warm gas self-pressurization system for liquid attitude and divert propulsion system, a transient model is developed using the modular modeling method. The system includes the solid start cartridge, pressure-amplified tank with liquid monopropellant, liquid regulator, gas generator, and pipes. The one-dimensional finite-element state-variable model is applied to the pipes and the lumped parameter method is adopted for the other modules. The variations of the system operation parameters over time during the startup, steady-state, and pulsing operational processes are obtained from the transient model, and the characteristics of starting time changing with different system parameters are also analyzed. It is shown that the system startup process can be divided into three distinct processes. The starting time monotonically changes with variations of the liquid regulator parameters, first decreasing and then increasing with the mass change of the solid propellant charge of the start cartridge, initial gas cavity volume of the pressure amplified tank and initial gas cushion of the propellant tank. The starting time can be reduced to less than 1.0 s (0.68-0.75 s for the current system). For meeting the deviation requirements of ±10% of the steady-state propellant tank pressure, the positive deviation requirement is assured by the self-locking pressure and the negative deviation can be assured within an allowable maximum propellant tank volume flowrate (1.6 times the design value for the proposed system) for downstream thrusters for a designed system. The results from the simulation are useful as a guide for further system design and testing.