Design, Development and Characterisation of piezoelectric microvalve for electric propulsion system

Abstract

The advanced geostationary communication satellites have shown trends in terms of increased power, life and payload mass. For these platforms, Electric Propulsion Systems (EPS) offer an attractive option for overall mass savings due to its high specific impulse and efficiency. The EPS is now being widely used for North South Station Keeping (NSSK) operations of such satellites. Xenon or similar gases are used as propellant in EPS for thrust generation. A dedicated gas Flow Control System (FCS) is used for mass flow rate control, flow isolation and pressure reduction during operation of EPS. At present these functions are carried out by a set of electromagnetically operated latching solenoid valves in combination with flow restrictors. A valve based on piezoelectric technology combines all the above functions in one unit and offers considerable reduction of total mass and size of FCS over the state of the art systems. This research work describes the design, configuration of development models and performance test results of piezoelectric valve for space applications. Detailed review of micro valves developed elsewhere for similar applications is carried out and their performance is compared in terms of critical functional requirements. Also the comparison of various technologies used for valve actuation is carried out for actuator selection. The design approach to achieve critical functional requirements of satellite propulsion valve are discussed. Both conventional fine machining and silicon micro machining methods are adopted for realization of two different designs of valve. The detailed design, realization & testing is carried out for valves based on both realization methods. The valving unit design, various types of seat configurations are discussed to arrive at most suitable configuration. The design calculations for seat stress, flow area, actuator preload are enumerated. Also the method of gas flow metering proposed to be used for this application and effect of temperature on critical valve performance parameters is discussed. The design of this valve is highly scalable and can be adopted to cater gas flow requirements from 3 mg/sec to 300mg/sec and operating pressures from 3 bar to 150 bar. The results of helium leak tests carried out at various stages of life cycle testing, flow repeatability test, flow stability test and flow tests at various operating temperatures are given. Based on life cycle test results, the valve operating cycle with increased cycle life is proposed. The valve stroke is measured using optical sensor to derive the actual flow area. Based on actual flow area and measured flow rates, the coefficient of discharge (Cd) for different valve strokes is estimated. Finally the conclusions & ongoing future work is discussed with other spin-off applications.