Anticipated future spacecraft requirements have motivated research on high power, high voltage dc to dc power processors. Therefore, a LC series resonant inverter utilizing silicon-controlled rectifiers (SCR's) or thyristors as power switches has been developed as the main power stage of the ion engine power processor over an input of 200 to 400Vdc, and an output of no load to 2.5KW. Because of sinewave currents in the thyristors and self commutation by means of the LC series resonant circuit, operating frequencies up to 20 Kilohertz have been demonstrated. A screen supply breadboard operating at 20KHz and using 3-year old thyristors was tested at 90% efficiency. The estimated efficiency at 10KHz and using presently available interdigitated and amplifying gate thyristors is 94%. Protection of power source and power semiconductors from current surges is inherent during startup and output overload or arcs due to the current limiting action of the series resonant tank. This inherent current limiting feature of the series resonant inverter, the ruggedness of the thyristors and the large derating factors which are achievable with thyristors,insure optimum power systems, power processing equipment and component reliability. A complete power processor utilizing series resonant inverters was produced for the 30cm mercury ion engine. Thermal vacuum operation and integration with a 30cm ion engine has been demonstrated.