0-7803-7454-1/02/$17.00 ©2002 IEEE 30.3: Thin Film Strain Gauge Sensors for Ion Thrust Measurement R. John Stephen and K. Rajanna * Department of Instrumentation, Indian Institute of Science, Bangalore-560 012, India. Vivek Dhar, K.G. Kalyan Kumar and S. Nagabushanam Control Systems Group, ISRO Satellite Centre, Bangalore-560 017, India. * Corresponding author E-mail: kraj@isu.iisc.ernet.in Abstract: In order to measure the thrust produced by a Stationary Plasma Thruster, a measurement system has been developed using a thrust balance with thin film strain gauge sensors. For this purpose, strain gauges were designed and deposited on the columns of the thrust balance fabricated and necessary signal conditioning circuit has been used. Performance of the system developed was studied, in a vacuum chamber under space simulated conditions, by activating the thruster. Insitu calibration was done using Lami’s principle. For discharge powers varying from 210-275 Watts, the measured values of thrust were found to be in the range of 11-16 mN with an accuracy of ± 1mN and resolution of 0.12 mN. Specific impulse and efficiency were also estimated. ------------------------------------------------- 1. Introduction In space applications, a kind of propulsion is used to re- orient satellites placed in orbits. In recent years, Hall type of electric propulsion devices such as Stationary Plasma Thrusters (SPT) placed on board the satellites are activated for the purpose of station keeping and on-orbit maneuvering [1-7]. In such situations, measurement of thrust is an important requirement. Techniques have been developed for the measurement of thrust produced by electric propulsion devices based on spring force, pendulum and a gas–bearing turntable [8-14]. Recently, we have reported the measurement of thrust produced by an SPT, using a thrust balance with conventional foil type of strain gauges [15]. In comparison with conventional foil type strain gauges, thin film strain gauges offer several advantages. Some of the advantages are absence of adhesive material, flexibility to tailor the properties of the sensor material in thin film form, good linearity and improved strain sensitivity etc. [16-17] In the present paper, we report the attempt made to measure the thrust produced by an SPT by developing a measurement system using a thrust balance with thin film strain gauges made of platinum–tungsten (Pt-W) material. This material has been chosen because of its high sensitivity, good repeatability and excellent linearity. The details of the experiments carried out to study the performance of the thrust measuring system on the ground under space-simulated conditions and the results obtained are reported. Figure 1. Schematic of the thrust balance assembly. 2. Thrust Balance assembly The schematic of the thrust balance assembly developed is shown in figure 1. It consists of a stainless steel (SS) plate at the bottom with four columns of beryllium-copper alloy, mounted one on each of the four corners, simply supporting another SS plate at the top. Its bottom plate is stationary and its upper plate moves in response to a force while remaining parallel to the bottom plate. When the thrust balance is critically loaded, the columns buckle and even a small force in the transverse direction produces a large deflection of the columns, the deflection being proportional to the magnitude of force acting on them. An SPT was placed on the upper plate along with additional weights, so as to critically load the thrust balance in such a way that the four columns share the total load equally. To provide damping during the operation of the thruster, a viscous damper was provided. More details of the thrust balance are provided in our earlier paper [15].