MHD arcjet onset studies

The phenomenon of onset in MHD arcjets is studied. An earlier solution procedure is combined with an onset criterion to obtain the onset boundary curves for hydrogen and argon. The onset boundary curves are in qualitative agreement with experimental results. It is found that the engine-specific impulse at onset can be increased by increasing the propellant low-temperature electrical conductivity. For plasma temperatures in the range 8000-12000 K, it is predicted that a higher specific impulse at onset should be obtained for hydrogen than for argon.