Gas-Surface Interaction Model Influence on Predicted Performance of Microelectromechanical System Resistojet

Abstract

The free molecule micro-resistojet was designed as a micropropulsion system capable of performing attitude controlandprimarymaneuversfornanospacecraftwithmasslessthan10kg.Thedetailsofgas ‐surfaceinteractions between propellant molecules and surfaces held at elevated temperature are critical in predicting the propulsion system’ s performance and efe ciency. The aim is to assess parametrically the performance of a typical thruster geometry using a general Maxwell scattering model and two versions of the Cercignani ‐Lampis‐Lord model (Lord, R. G., “ Some Extensions of the Cercignani ‐Lampis Gas‐Surface Scattering Kernal,” Physics of Fluids, A , Vol.3,No.4,1991,pp.706 ‐710 andLord, R.G., “ SomeFurtherExtensionsoftheCercignani ‐LampisGas‐Surface Interaction Model,” Physics of Fluids, A , Vol. 7, No. 5, 1995, pp. 1159 ‐1161). The models are incorporated into a direct simulation Monte Carlo numerical code and are used to bound the predicted performance characteristics of the thruster. The total specie c impulse varies by approximately 20% over range of accommodation coefe cients from specular to diffuse surface scattering. However, there was only a maximum difference of about 5% between the models for a given accommodation coefe cient. Other more microscopic parameters, such as axial velocity distribution functions, appear to depend more on the scattering model assumed.