Ground testing of satellite control thrusters at high altitude conditions

Abstract

Satellite control thrusters are designed to operate at upper atmosphere, where a low pressure environment prevails. During ground testing of such a thruster, the low pressure environment corresponding to the flight situation has to be produced in the vicinity of the rocket thruster with the help of an ejector- diffuser system. The ejector- diffuser may employ the momentum of the rocket exhaust gas and also those of high speed jets issuing from external ejectors, for evacuating the test chamber environment to low pressure. A series of shocks occurring in the diffuser portion aid in the sealing of the evacuated environment and for achieving gradual pressure recovery from the low vacuum level to atmospheric pressure. In the case of small thrusters used in satellite applications, the momentum of the rocket exhaust is too small to create the desired vacuum and a multistage ejector is required to share the evacuation load. In the current study, an attempt has been made to numerically investigate the performance of an ejector- diffuser employed to test large area ratio rocket thrusters. Initially, a decoupled steady state analysis has been carried out to analyze the performance of the multistage ejector system at no- flow and full flow conditions of the rocket motor. Later, simulation has been performed for the rocket motor coupled with the vacuum chamber and the diffuser system. The numerical predictions are validated with available in- house experimental data.