Arcjet thruster development

For several years an intensive program has been in progress at the University of Stuttgart to investigate and develop thermal arcjets for propellants including ammonia, nitrogen-hydrogen mixtures simulating hydrazine, and hydrogen. Since hydrogen yields the highest specific impulse I-sp and best efficiencies eta, special emphasis was placed on this propellant. Arcjet power levels between 0.7-150 kW have been studied, including water- and radiation-cooled laboratory models and flight hardware. Results yielded a maximal attainable I-sp as a function of the design and power level and showed that increasing power increased I-sp. Radiation-cooled arcjets show better eta and I-sp than water-cooled devices, but raise technical problems because of the high temperatures of the thrusters, which require the use of special refractory materials. Proper arcjet optimization was done with a thorough thermal analysis, including the propellant flow. A further improvement of these thrusters was reached by regenerative cooling and by optimizing the constrictor contour. The constrictor now is modeled by a three-channel model, the results of which are compared with experimental data. A new two-dimensional computational fluid dynamics (CFD) approach for hydrogen arcjet thrusters is presented. In 1996 a 0.7-kW ammonia arcjet is scheduled for a night on the P3-D AMSAT satellite.