The performance of a two-stage ejector during high-altitude testing of large-area-ratio satellite thrusters is numerically investigated. Since the flow rateof the exhaust from the satellite thrusterisvery low, self-ejector action of the exhaust is quite weak; therefore, a two-stage external ejector is required to create the desired low vacuum in the test chamber. The present work attempts to investigate the effects of various operational and geometric parameters on the performance of the two-stage ejector. Predicted results show that the downstream ejector (E2) operation is more critical for maintaining the required vacuum. However, for optimal performance, it is possible to tune the parameters such that both ejectors deliver the same suction effect. Maximum performanceofeach ejector is obtained when the primary jet expanding from the nozzle smoothly seals the mixer throat against backflow. Employing a low molecular weight fluid and high stagnation temperature helps in reducing the quantity of fluid required for test facility evacuation. Useful correlations have been derived to quantify the suction performance of the two-stage ejector, and the predicted results compare well with in-house experimental data. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.