Design of Test Bench for Measurement of Thrust and Impulse Bits of MEMS-based Micro-thrusters

Koopmans, 2010). Problems in indirect measurements are associated with unknown elasticity of the momentum exchange between the exhaust plume particles and the target (Jean-Yves, 2006). Thrust measuring techniques can use force transducers or measure the deflection of the pendulum through different approaches. Load cells are widely used in modern day test benches (Lamprou, Lappas, Shimizu, Gibbon, & Perren, 2011; Pancotti, Lilly, Ketsdever, Aguero, & Schwoebel, 2005). They work well for high thrust devices, but in the case of micro-thrusters which have low thrust to mass ratios, the load cell measurement is affected by the thruster weight (Polk et al., 2013). The availability of load cells with sufficient sensitivity permitted their introduction to low thrust measurement applications. Advantages conferred through the use of load cells are high accuracy over a wide measurement range due to their high degree of linearity, the limiting of thrust stand motion to very small values, and prompt readings. There is no need for time-consuming force-displacement calibrations during which thermal drift may introduce uncertainty into the measurement (Pancotti et al., 2005). Steady state thrust measurement is increasingly becoming popular, particularly with more accurate and sensitive controls being developed. The method is to determine an unknown force in a laboratory environment and track slowly developing variations in that force. A steady state null balance accomplishes this by applying a control force to cancel thrust stand deflection caused by the unknown force (Janssens, 2009). When deflection has been nullified, the control force is assumed to be equal to the unknown force. However, the use of the system is limited because of inaccuracy that may be introduced by the controls themselves. Thrust and impulse benches that are currently used are classified based INTRODUCTION The requirement for precise positioning and movement of satellites is increasing with the advancement in space technology and the last decade has seen a steady increase in interest in microtechnology. This, in turn, has increased the need for precise thrust and impulse measurement techniques for micro-scale thrusters and considerable effort is being invested to achieve precision (Mueller, Hofer, & Ziemer, 2010; Spence et al., 2013). The sensitivity and accuracy of a thrust bench depends on its mode of measurement and the sensor itself. Direct and indirect measurements are both used today, but direct measurements are given preference because of better precision in the case of microsatellites. If the thruster itself is mounted on the bench, it gives direct measurement of the force, but if the exhaust of the thruster is used to produce deflection, it is an indirect method (Bijster, 2014; Janssens, 2009; Zandbergen, Janssens, Valente, Perez-Grande, & Design of Test Bench for Measurement of Thrust and Impulse Bits of MEMS-based Micro-thrusters