Measurement of thrust induced by a water-fueled magnetron sputtering source

Development of a compact electric propulsion device is a key issue for orbital control of small satellites. In general, gaseous propellant introduced from a high-pressure gas storage tank is ionized and the ions are accelerated and exhausted from the system. To avoid the charge up of the satellite and the resultant spontaneous formation of the electric field pulling back the ions, a neutralizer has to be mounted as often used in gridded ion thrusters and Hall effect thrusters. Various approaches have been made for compact thrusters, such as liquid and solid propellants, a neutralizer-free radiofrequency thrusters, vacuum-arc thrusters, and so on. One of the authors has reported the thrust generation by a magnetron sputtering source, where the electrically neutral sputtered particles are responsible for the thrust generation. These results implies that the magnetron sputtering source does not require the neutralizer to obtain the thrust, while argon gas propellant has still been used to sustain the discharge. Here we report the operation of the magnetron sputtering source with a liquid water propellant and the induced thrust is assessed by using a target force stand. The results show the thrust-to-power ratio of about 3-4 mN/kW and the power level of the discharge is about 80 W.