Thrustors for Low Acceleration Nuclear Electric Rockets

Technological progress in the development of electric propulsion thrustors during the past several years has been quite rapid, and as a consequence the performance potential of a broad spectrum of thrustor types has been fairly well delineated. Thrustor types include electrostatic thrustors, i.e., ion propulsion devices utilizing either surface or electron bombardment ionization sources and devices which utilize charged colloids as propellant; electrothermal thrustors, i.e., arcjets and resistojets; electromagnetic thrustors, i.e., pulsed or steady state devices utilizing predominantly magnetohydrodynamic forces for acceleration; and so-called hybrid thrustor types, in which are wed electrothermal and electromagnetic techniques, as exemplified by the so-called "Harcjet" or "thermo-ionic rocket". Those thrustor types from this spectrum which presently appear most promising are discussed, together with a brief description of their operating mechanisms, performance results, and the major technical trends, unsolved problems and future directions of this field as viewed by the author. The important early missions for these thrustors are briefly summarized, together with some new concepts for electrical propulsion systems, and criteria are presented for the selection of an electric thrustor type or types from this spectrum of choices for different types of missions. The viewpoint adopted throughout is that for the nonspecialist in this field.