Physical electronic phenomena in ion propulsion engines

The ion engine offers one of the most promising techniques for long-duration space propulsion, for missions ranging from the prime propulsion of manned interplanetary vehicles to the control of earth satellites As we look ahead to the more ambitious missions that man will wish to accomplish in space — the missions requiring longer times and therefore greatest propulsion energy — we seek a reaction rocket with a high propellant exhaust velocity. This high velocity allows the generation of thrust with relatively less consumption of propellant, with significant advantage to the mission in the additional payload capability of the spacecraft as less propellant is required. The only way presently known to obtain propellant exhaust velocities significantly higher (by a factor of 10 to 100) than those of current chemical rockets is by means of the acceleration of charged particles. In principle, electrical acceleration can provide essentially any exhaust velocity, by proper choice of the particle mass and the accelerating voltage. In practice, however, the engines that have reached the highest state of development and currently show the greatest promise use heavy ions (having atomic masses of approximately 100 to 200) as the propellant, accelerated through 3000 to 10 000 volts.