Microarcjet Microthruster for Nanosat Applications (Preprint)

摘要

This paper summarizes experiments and analysis of the micro- discharge microarcjet thruster. A small, very low power (2-5 Watt) micro- discharge was maintained between two electrodes in geometries compatible with application to a cold gas thruster. To evaluate the efficiency of the discharge in providing an increase in Isp and thrust, a special torsional micro-balance thrust stand, capable of micro-Newton resolution, was designed and constructed. The micro-balance thrust stand was installed in a large dielectric chamber with high pumping speed to eliminate stray coupling of the discharge with the vacuum chamber or background gas. A battery operated driver provided the 240-280 volts required to sustain the very low current (5-40 mA) arc discharge. The discharge was also ballasted inductively to avoid capacitive effects as well as resistive losses. Thrust measurements using a variety of electrode geometries and propellants were carried out. It was found that the optimum scale for the discharge bore for these low power levels was approximately 300 micron. Smaller bores resulted in too large a power loss in thermal transfer to the thruster/nozzle body. A larger bore led to large mass flows at the pressures required to produce a stable discharge. All ring or cavity electrode structures showed no appreciable gain and were rapidly eroded by the discharge. The only electrode configuration to show an increase in thrust from the application of the discharge with no measurable electrode erosion was in a configuration similar to the standard arcjet. Most of the studies were conducted in Argon, but other gases from H to Xe were also used. In Argon the optimal mass flow was approximately 2 mg/s with between 10 to 20 kPa upstream of the nozzle.