Cathode effects on thrust subsystem performance predictability.

Development of a model of mercury vapor electron bombardment thrustor hollow cathode operation. The proposed model predicts that the primary electron emission mechanism is thermionic when sufficient low work function material is present, that the cathode is heated by power extracted from the plasma to a temperature sufficient to emit the current demanded by the external circuit; that for a given total arc current, attempts to reduce cathode temperature by changes in the external thermal coupling will affect only the amount of power extracted from the plasma; and that depletion of low work function material in the cathode results in higher cathode temperature.