ARCJET THRUSTER DEVELOPMENT

For several years an intensive program has been in progress at the Uni versity of Stuttgart to investigate and develop thermal arcjets for pr opellants including ammonia, nitrogen-hydrogen mixtures simulating hyd razine, and hydrogen. Since hydrogen yields the highest specific impul se 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 ha rdware. Results yielded a maximal attainable I-sp as a function of the design and power level and showed that increasing power increased I-s p. Radiation-cooled arcjets show better eta and I-sp than water-cooled devices, but raise technical problems because of the high temperature s of the thrusters, which require the use of special refractory materi als. Proper arcjet optimization was done with a thorough thermal analy sis, including the propellant flow. A further improvement of these thr usters was reached by regenerative cooling and by optimizing the const rictor contour. The constrictor now is modeled by a three-channel mode l, 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 sche duled for a night on the P3-D AMSAT satellite.