Some Problems in Ionic Propulsion Systems

Some of the problems and applications of ionic propulsion systems are discussed. Three different systems' optimization criteria are considered: the maximization of the initial acceleration of a space vehicle; the minimization of the total-mass-to-payload-mass ratio; and the minimization of the propellant mass required to refuel the vehicle. The production, acceleration, and neutralization of beams of singly-ionized cesium ions is also discussed in limited detail. A hot tungsten contact-catalyst type of ion source is assumed and some experimental results with such a source are reviewed. Finally, a simplified treatment of the space charge neutralization of a positive ion beam in the region behind the space vehicle is presented. In this treatment, the positive-ion beam is replaced by an infinitely-long cylinder of uniformly-distributed positive charge. Electrons are emitted from an annular filament encircling the perimeter of the beam. It is shown that this approximation leads to radial oscillations of the electrons through the positive column.