Advanced Power Conditioning for an Ion Propulsion System

Space programs proposed for the period 1970 to 1980 include plans for transporting large payloads to the near planets, such as Mars, and to even greater interplanetary distances. The accomplishment of these missions in a reasonable travel time will require» specially designed, continuous-thrusting propulsion systems. Three types of systems are envisioned: chemical, nuclear, and electrical. Of the three, the electric propulsion system is certainly the most advanced and by far the most attractive in terms of potential development. The electric systems, which have the highest specific impulse, provide a maximum payload in terms of propulsion system weight. In any electric propulsion system, the engine and power conditioning must be developed as an integral unit. Ion engines are small, lightweight devices and the weight and size of the power conditioning often detracts from them. Furthermore, while space operation of ion engines has been successfully demonstrated by both the Air Force and NASA in short ballistic flight tests, their ability to operate in space for extended periods of time under actual mission conditions has yet to be demonstrated. Electro-Optical Systems, in designing the advanced ion propulsion system discussed in this paper, had three prime objectives: reliability, low weight, and extended operational life. A study program was first undertaken to determine the optimum size of the thrusting system for a specific Mars mission; the results indicated 3 .kW systems to be optimum based on state-of-the-art electronic devices. One of the most significant problems with any ion engine power conditioning system is the containment of the high voltages while operating in a vacuum. This problem was successfully solved in the next phase of the program when a system was built which was capable of extended operation in vacuum, although not packaged for flight