Electric Propulsion (EP) is a form of advanced rocket propulsion that uses electrical
energy for heating and/or directly ejecting propellant. EP was pioneered by
Professor Robert Jahn, one of the leading propulsion engineers in the world,
at Princeton University, New Jersey, USA in the 1960s, 1970s and 1980s. EP
provides much lower thrust levels than conventional chemical propulsion (CP) does,
but much higher specific impulse. This means that an EP device must thrust for a
longer period to produce a desired change in trajectory or velocity; however,
the higher specific impulse enables a spacecraft using EP to carry out a
mission with relatively little propellant and, in the case of a deep-space probe,
to build up a high final velocity. The source of the electrical energy for EP is
independent of the propellant itself and may be solar (see solar-electric propulsion) or
nuclear (see nuclear-electric propulsion). The 4 main components of an EP system
are: an energy source, a conversion device (to turn the source energy into electrical
energy at an appropriate voltage, frequency, etc.), a propellant system (to store and
deliver the propellant), and one or more thrusters to convert the electrical energy into
the kinetic energy of the exhaust material. Naheem Choudhary (Final Year Project,
BEng (Hons)) under the guidance of Dr. Os Bég has investigated the various EP
systems, performing a detailed critique of the best and most practicable for 21st
century interplanetary missions. Below – left: The MIT Ion Thruster – courtesy
Professor Martinez, MIT Space Propulsion Laboratory
Below right top - EP thruster for spacecraft –courtesy Princeton University.
Bottom left- proposed ESA-NASA spacecraft exploiting ion propulsion.