Design And Study On The Low-power Water Propellant Pulse Plasma Thruster

Pulsed Plasma Thruster (PPT), as one of the electric propulsion systems which, for its excellent properties, is increasingly taking the place of the traditional chemical prolusion system and being widely used in maneuvering and controlling thrust of spacecrafts, has the characteristics of higher specific impulse, lower power dissipation, structure simplicity, light weight, good system inheritance and reliability, etc. and becoming one of the hot spots in international electric propulsion research. However, in the typical Pulsed Plasma Thruster which uses Teflon as the refrigerant, there exist some problems such as low velocity steam, low propulsive performance caused by large particle divergence, the pollution of spacecraft equipment by carbon and fluorine produced by Teflon ablation, which limit the PPT's practical application. As a result, it is worthwhile to develop a PPT with free pollution, high performance and extensive applicability.The dissertation studies the propulsive mechanisms of the low-power water propellant PPT from its external circuit, the design and manufacture of noumenon structure, the working characteristics and performance, and the approach of improving the performance, etc. and achieves the following results:The mass flowrate under the magneto-acoustic condition and speed function of magneto-acoustic point are established. By discussing the influence of the propellants of gas-liquid-solid morphologies on PPT's performance, the dissertation points out that water is the optimum propellant for improving the performance of low power PPT. Based on analyzing the physical models of water propellant PPT, the noumenon structure, main discharge electric circuits, the design of triggering device, the experimental system of water propellant PPT is set up.The numerical analysis of working process of water propellant PPT in the electromagnetic acceleration model is carried out by combining the circuit model of the fixed parameter and that of the variable parameter; the influence of the structure parameter of external circuit on performance is discussed; the measurement system of discharge circuit is built; by the measurement of discharge circuit the working characteristics such as the electric discharge type, work energy threshold etc. and the influencing factors of discharge parameters on performance are analyzed. From the angle of thrust generating mechanism--the thrust is manufactured by the Joule heat and the electromagnetic force, based on zero-dimensional model and by the measurement and theoretical analysis of the micro-impulse and plasma equivalent resistance of low-power water propellant PPT, the impact of thrust-to-power ratio, energy distribution and efficiency on the promotion mechanism is studied. The micro-impulse measurement experimental system of water propellant PPT is built; the impulse equilibrium model is set up; the vibration velocity of plume crashing on horizontal is measured and its impulse is calculated; the comparative analysis between the thrust-to-power ratio calculated by applying impulse theoretical formula to discharge current value and that calculated by practical measurement of impulse value is carried out. The theoretical analysis of dispersal behavior of the production and expansion of the plasma in the discharge process of water propellant PPT is carried out. Combining with the circuit model of the fixed parameter, the energy balance relation, the conversion of Joule heat from energy storage and the conversion rate of electromagnetic acceleration in the operating process of water propellant PPT are derived; the conversion rate of energy storage conversing into Joule heat and the electromagnetic acceleration in the operating process of water propellant PPT is obtained by the measurement of discharge current.The mechanism of easily ionized elements Matrix interferences and its impact on plasma electromagnetic acceleration is studied, and a new approach is put forward for the improvement of the propellant performance by the addition of easily ionized elements Na and K into the water propellant, and its feasibility is verified by the measurement of discharge current and the analytical experiment of emission spectrum.