Rockets, Ion Propulsion

Abstract

Electric propulsion, the propelling of space vehicles by streams of electrically charged and electrically accelerated particles, is one of the most exciting concepts of the space adventure. It represents a fascinating area of applied science and technology, and it also provides the only feasible means of exploring the farthest reaches of our solar system by economically transporting large manned expeditions and heavy payloads to neighboring planets and probing the solar system away from the ecliptic plane. The concept of the ion rocket engine (the most useful form of electric propulsion for space missions) has existed for some time. However, the concept had to remain of only academic interest until the advent of the space age, and, particularly, until generating large amounts of electric power in space became a physical possibility. When solar–electric power source technology was established, the latter requirements, of course, became fulfilled. In general, an electric propulsion system has a power plant that consists of an energy source and a means of converting this energy into electrical energy and a propulsion device that converts the electrical energy into directed kinetic energy of its propellant. The two major problem areas of electric propulsion are ( 1 ) the development of sources of electrical energy that are sufficiently lightweight and ( 2 ) the transfer of this energy to the propellant to provide high exhaust velocities efficiently. The first problem, along with the general need for power in space, has given strong impetus to fundamental and applied work in developing lightweight solar panels. These areas of research and development have been vital to the future of electric propulsion and obviously have impacted many other important satellite and spacecraft applications. A solution to the second problem, an efficient propulsion device, is the subject of this article. Generic types are discussed. The electron‐bombardment ion thruster is the most mature and the most tested and is a major focus of this article. A sampling of results from space missions are reviewed.