A Working Arc Jet Rocket Engine
- Paper ID
IAF-60-25
- author
- company
AVCO corporation
- country
U.S.A.
- year
1960
- abstract
The purpose of this paper is to present experimental results on the performance and operating life of a 30-kW plasma jet rocket engine for space propulsion. The arc jet rocket engine is currently the simplest of the different proposed electric propulsion devices. The working fluid is injected into the arc chamber, heated by Joule heating as it passes through the discharge, and is expanded through a conventional nozzle. The nozzle serves to convert the ohmic heating in the.electric arc discharge into kinetic energy. No effort is made to produce thrust by the interaction of electromagnetic fields and the working fluid. The arc jet engine is basically similar to the chemical rocket differing only in that energy is introduced into the arc chamber by a continuous electric discharge rather than by chemical reaction. An arc jet rocket engine consisting of a special-geometry tungsten-composite cathode and water-cooled anode has been operated continuously in our laboratory, using both helium and hydrogen as working fluids, for periods of the order of 50 hours. The engine has the following average performance specifications. Thrust Level 0.50 to 1.0 pound Specific Impulse 750 to 1500 seconds Power Level 25 to 35 kilowatts Overall Efficiency (electric to kinetic) 25 to 75 percent For both hydrogen and helium the overall efficiency of conversion of electric to kinetic energy decreases with increase in the mean gas enthalpy. On the basis of this observation, since the degree of dissociation and/or ionization of either helium or hydrogen increases with enthalpy, it is probable that at least a fraction of the energy absorbed in dissociation and ionization is not converted to kinetic energy during the expansion process. The onset of frozen flow is further confirmed by the observation that helium, which cannot be dissociated and has a relatively high ionization potential, has a significantly higher energy conversion efficiency than easily dissociated hydrogen.