Study On New High-efficient Micro-propulsion Technology

Multiply small satellites can make up of a team of formation flying and then accomplish a mission that an expensive big satellite can not. It is crucial for Formation flying of small satellites to keep in very precise position and orientation. Then small satellites need to control their track and attitude precisely. They need very small thrust, usually milli-Newton. even micro-Newton.In this article our objective is to develop a high efficient hydrogen dioxide micro-propulsion system aim to apply on a nano-satellite of tens of kilogram. The research includes a self-pressurizing fuel tank, fabrication of a MEMS-based microthruster and thrust measurement in vacuum, using optical microscope and high-speed camera to observe the flow field in the chip, etc.Propulsion system usually takes up a large fraction of weight of a satellite. The traditional propulsion system contains many components such as high pressure pressurant bottle, pressure regulator and so on. It is hard to microminiaturize traditional propulsion system. In this article a self-pressurizing fuel tank is invented. It use a micro-heater to heat to decompose NH4HCO3 and generate gas to increase the pressure of the fuel tank. This structure of the system is simple and the weight is light. It is easy to be microminiaturized.In this article, we design a MEMS microthruster chip B. This chip's fluid path is not straight and symmetry, as usually, instead, it has a S shap of flow path. This design make the fuel stay more time in the chip; the catalyse chamber is made up of micro-pillar array. The micro-pillar array greatly enlarges the catalystic area, and increase the decomposition rate. The whole chip B is compact, can use the reaction heat efficiently, and reduces the heat loss.A micro-thrust test stand in vacuum was setup. It adopts a lever to enlarge the micro-thrust force and a vacuum oil damping system to reduce the noise from surrounding. Through experiments, we found that the impinging force reaches a plateau section with the increase of impinging distance if only the impinging plate is big enough. In the plateau section, the impinging force is almost equal to the thrust force. Then, one can measure the impinging force instead of the direct thrust force measurement. By this method, the disturbance of connecting lines is avoided completely.At last, we use chip A as nozzle, adding Pt silk as accessorial catalystic surface, and equipped with electronic heater, to prepare a H₂O₂ micro-thruster. The problem of the silicon chip connected with stainless steel component is addressed. Then the micro-thruster is tested. The micro-flow rate of the micro-thruster is measured by liquid column differential pressure method. The test result show that this kind of micro-thruster can produce 4～5 mN thrust force with 2～3 bar inlet pressure; the specific impulse reach about 200 s with 2～3 w heating power.