Analytical and experimental investigation of satellite thruster vacuum performance employing supersonic ejectors

The present study is carried out to investigate the performance of a cold gas thruster operating under the vacuum with a high expansion ratio. A pressure recovery system employing diffuser and multistage ejectors is employed to evacuate a vacuum cell whose pressure is an indicating parameter of an operating altitude (i.e. nozzle exit condition). The cold gas thruster has an expansion area ratio of 60. For ejector design, the parameters like the length to diameter ratio ( L / D e ) and ejector nozzle stagnation pressure ( P tot ) seem to have significant importance, and their effects on vacuum cell pressure are studied by using both analytical and experimental techniques. Role of second throat type diffuser in the overall pressure recovery is also investigated. The required exit pressure is achieved by a two-stage ejector system having constant area mixing chambers. The ejectors’ stagnation pressures are considered from 12 to 20 bars, while ( L / D e ) is considered from 4.5 to 15 and 2.5 to 16.5 for Ejector-1 and Ejector-2, respectively. Minimum vacuum cell pressure is achieved with the ( L / D e ) of 7 and 9 and stagnation pressure ( P tot ) of 18 and 20 bars for Ejector-1 and Ejector-2, respectively. The thrust coefficient (CF) and the specific impulse (Isp) were found in good agreement with the theoretical results.