The use of an ion-drive for the propulsion of space vehicles was first proposed as far back as 1906 by Dr. Robert Goddard, the father of American rocketry, although at the time the science was not far enough advanced for practical applications. Due to continued research, working ion engines were developed by the late 1950s and actually used on some of the early satellites in the 1960s. The first in-space demonstration of a working ion engine was carried aboard the SERT-1 spacecraft, which was launched in 1964. The picture at upper left is of NASA.s latest ion engine, which is intended for use by deep-space probes carrying research instruments and possibly one day man himself.
Unlike chemical rockets, from the tiny ones Robert Goddard developed in the 1920s to the massive Saturn-V which sent men from the earth to the moon in the 1960s and 70s, ion engines do not rely on the mixing of chemicals to produce a controlled explosion to power a massive rocket into space. They work on the same principle that Issac Newtown discovered, that for every action there is an equal and opposite reaction, but instead of using a chemical reaction to provide the thrust, an ion engine instead uses electrons (in this case, from xenon atoms) that are ionized by a strong magnetic field to provide a stream that produces a small but steady thrust, similarly but on a much larger scale as an ordinary home air ionizer. This is more efficient than using chemical rockets, as well as being much safer.
If an ion-engine has so many advantages over a standard chemical rrocket, you might be asking yourself, why isn’t it being used more. The answer is, it is being used. An ion engine is currently propelling NASA’s Dawn spacecraft on its’ mission to explore the asteroid Ceres. Japans’s Hyabusa probe, which gathered samples from the asteroid Itakowa in 2005 was also ion-powered, as was NASA’s Deep Impact probe which purposely struck a comet to determine its’ composition. But the larger answer to the question is that, while ion-engines are very efficient and reliable, up to now there has been a limit to their power, so they haven’t been able to be used to, for example, launch a satellite from the surface of the earth. Since their thrust is much less than that of a standard rocket, they also aren’t as fast, though if the thrust can be kept up for a long time as in, for example, the case of a deep-space probe, they can achieve very high speeds because their ionic thrust is must faster than that of a chemical rocket. NASA is considering more advanced versions of the ion engine for such tasks as sending supply ships to the asteroids or even to colonies on other planets, such as Mars, when they have been established. It is also considering using an ion-powered spacecraft to capture a small nearby asteroid and shove it gently into near-Earth orbit, both for scientific reasons and so that astronauts can get a chance to practice in preparation for a voyage to the asteroid belt. So while it may not be as glamorous as a warp-drive, the ion engine is poised to play a very significant role in mankind’s conquest of space.