High power microwave sources are now available and usable, with modification, for beamed energy propulsion experiments in space. As output windows and vacuum seals are not needed space is a natural environment for high power vacuum tubes. Application to space therefore improves reliability and performance but complicates testing and qualification. Low power microwave devices (TWT, etc) have already been through the adapt-to-space design cycle and this history is a useful pathway for high power devices such as gyrotrons. Microwave propulsion devices require ionized component from 10 to 100 ppm in order to transfer beam energy to propellant. Two types of ionizers are considered in this paper. First, the arc jet device is space-qualified as propulsion device but consumes high power. Second, the microwave discharge ionizer creates in-chamber ions by injection of seed gas into one or more focal regions near the dome part of the chamber.