The Effect of Ignition Techniques on a Capillary Discharge Based Pulsed Plasma Thruster

In order to better understand the operating characteristics of a capillary discharge based electrothermal pulsed plasma source, a variety of ignition techniques were investigated to determine performance effects and viability in a real system. Discharge current profiles along with thrust and specific impulse measurements were obtained to take a detailed look at ignition caused by an exploding wire, the Paschen breakdown of gas, and a surface flashover caused by the addition of a third electrode. Experimental testing showed that there are only slight performance differences between the three techniques, however, the surface flashover ignition method is currently the best option for adapting the capillary discharge to space applications due to reliable and repeatable operation. Capillary discharge plasma sources utilizing the surface flashover ignition method showed propulsion efficiencies of 8-18% within an Isp range between 350 and 650 s with no nozzle expansion or material optimization. While these numbers do not match performance predictions in work by Burton, it is believed that material optimization and the addition of an expansion nozzle will exceed all previous experimental efficiencies. Additionally, the development of the surface flashover ignition system has provided important insight into the response of capillary discharges to ignition conditions and techniques. For presentation at the AIAA Joint Propulsion Conference and Exhibit (45th) held in Denver, CO on 2-5 August 2009.