Ion propulsion is a form of electric space propulsion in which ions are accelerated by an electrostatic field to produce a high-speed (typically about 30 km/s) exhaust. An ion engine has a high specific impulse (making it very fuel-efficient) but a very low thrust. Therefore, it is useless in the atmosphere or as a launch vehicle, but extremely useful in space where a small amount of thrust over a long period can result in a big difference in velocity. This makes an ion engine particularly useful for two applications: (1) as a final thruster to nudge a satellite into a higher orbit and or for orbital maneuvering or station-keeping, and (2) as a means of propelling deep-space probes by thrusting over a period of months to provide a high final velocity. The source of electrical energy for an ion engine can be either solar (see solar-electric propulsion) or nuclear (see nuclear-electric propulsion).
Two types of ion propulsion have been investigated in depth over the past few decades: electron bombardment thrusters and contact ion thrusters. Of these, the latter remains in the research stage while the former has already been used on a number of spacecraft. Specifically, the variety of electron bombardment thruster known as XIPS (a Hughes/Boeing product) is used for station-keeping by some geosynchronous satellites, while the NSTAR ion engine (developed by NASA and Hughes) propelled the Deep Space 1 interplanetary probe.
One of the most promising new developments in ion propulsion is the DS4G (dual-stage 4-grid) ion engine
, developed by the European Space Agency and a group at the Australian National University. This was first tested by ESA in 2005. The DS4G thruster achieves much higher voltages to be used than previously thought possible, resulting in a more powerful post acceleration of the extracted ions. The thruster was tested in a large space simulation chamber in the ESA Technology centre in the Netherlands at a remarkable 30,000 V and produced an ion exhaust plume that travelled at 210 km/s – over four times faster than state-of-the-art ion engine designs achieve.
History of ion propulsion
On August 1, 1961, NASA awarded a contract to the Astro-Electronics Division of RCA to design and build a payload capsule for flight-testing electric propulsion engines. The program called for seven capsules, three for ground tests and four for actual flight tests. Each capsule was expected to carry two electric engines. The first was expected to carry one cesium-fueled ion-engine representing Stuhlinger's design with the Hughes engine. The second was expected to carry one mercury-fueled ion engine representing Kaufman's design with the Lewis engine. Plans called for the engines to operate from 1 to 2 kW of power. Hughes demonstrated an ion engine on September 27, 1961, at its research laboratories in Malibu. Stuhlinger was among those on hand to greet the scientific and technical writers who attended the event.
Ion propulsion in science fictionFrequent mention of ion propulsion has been made in works of science fiction for several decades. It was featured, for example, in a September 1968 episode of Star Trek called "Spock's Brain," in which invaders steal Spock's brain and flee in an ion-powered spacecraft.
Related categories ADVANCED PROPULSION CONCEPTS
ROCKET ENGINE TYPES
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