Space Propulsion Applications of Helium Arcjets

With currently available space electric power systems, the optimum specific impulse for electrically propelled satellite transfers from low Earth orbit to geosynchronous Earth orbit appears to be in the 1000 to 1200 second range. Arcjets operating with helium as a propellant may be the most efficient electric thruster capable of operating in this specific impulse range. This work reports on a recent set of experiments which examined the effects of arcjet configuration, and propellant composition and flow rates, on arcjet performance. In these tests, it was found that increasing the cathode-anode gap over that normally used with hydrogen or ammonia propellants increased arc stability and significantly improved specific impulse and electrical efficiency. Hydrogen seeding was found to improve arc stability, particularly at smaller cathode gaps, but it had a very small effect on overall performance of the arcjet. The primary variable which affected arcjet performance was found to be propellant flow rate. The efficiency of the helium arcjet was found to increase with increasing propellant flow rate up to the maximum flows available for the current set of experiments.