R.G. Jahn and E.Y. Choueiri (EPPDyL,
Full article in Encyclopedia of
Physical Science and Technology, 3rd Edition, Academic Press, San Diego,
v.5, pp. 125-141, 2002.
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The science and technology of electric propulsion (EP) encompass a broad variety of strategies for achieving very high exhaust velocities, in order to reduce the total propellant burden and corresponding launch mass of present and future space transportation systems. These techniques group broadly into three categories: electrothermal propulsion, wherein the propellant is electrically heated, then expanded thermodynamically through a nozzle; electrostatic propulsion, wherein ionized propellant particles are accelerated through an electric field; and electromagnetic propulsion, wherein current driven through a propellant plasma interacts with an internal or external magnetic field to provide streamwise body force. Such systems can produce an order of magnitude higher range of exhaust velocities and payload mass fractions than the the most advanced chemical rockets, thereby enabling or substantially enhancing many attractive space missions. Their attainable thrust densities (thrust per unit exhaust area) are much lower, however, predicating longer flight times and more complex mission trajectories. In addition, they require space-borne electric power supplies of low specific mass and high reliability, interfaced with suitable power processing equipment. Optimization of EP systems thus involves multidimensional tradeoffs among mission objectives, propellant and power plant mass, trip time, internal and external environmental factors, and overall system reliability. An enduring international program of research and development of viable electric thrusters has been in progress for several decades, and over the past few years has lead to the increasing use of a number of EP systems on commercial and governmental spacecraft. Meanwhile, yet more advanced EP concepts have matured to high credibility for future mission applications.