Prediction of the performance of a Si-micromachined microthruster by computing the subsonic gas flow inside the thruster

MEMS-based microthrusters are now introduced and fabricated to meet micropropulsion requirements especially for the attitude control of the nanosatellites. The key to the development of these microsystems lies in the generation of extremely accurate thrust level. This is made possible by modelling tools capable of predicting the processes inside the thruster during the subsonic combustion and of computing the theoretical performance of the systems. In this paper, we present a new model based on the computation of the unsteady gas flow inside the microthruster. The results show the evolution of the gas pressure, velocity and gas volume at each section of the thruster and at each step in the propulsion process. The final aim of this study is to obtain a model package capable of predicting the level of the exhaust thrust of any subsonic microthruster for any given geometrical features. For a glycidyle azide polymer (GAP)-based microthruster, the calculations yield the best subsonic micronozzle design: the divergent length ranges from three to seven times the throat radius for a divergence angle of 12°. The chamber-to-throat section ratio must be comprised between 5 and 10. Modelling results also show that, for a 4-mm combustion diameter thruster, the thrust force ranges from 2.5 to 75 mN, depending on geometrical characteristics.