In the ongoing search for ways to power spaceships, the ion engine has a long history of interest but still a long way to go to be usable.
The idea began with Robert Goddard, the pioneering rocket engineer who went on to design the first liquid fuel rocket, when he patented a theoretical design for an ion "thruster" in the early 1900s.
According to theory, ion engines create thrust by feeding inert gases like krypton or argon into a chamber in which a tremendously powerful electromagnetic field strips one electron from each atom of the gas. This process, known as ionization, gives atoms an electric charge that allows a set of magnets in the thruster to accelerate them out the tail of the chamber.
While ion engines do not have the tremendous kick at ignition that nuclear-powered rockets do, their acceleration is constant, and, given enough time and room, they can reach speeds of several hundred miles a second.
The technology for ion engines has yet to be developed practically. Such engines require generating millions of watts of power at a steady rate over long periods of time, and that is extremely difficult to do in space, where electrical power sources are limited.
