The Ion Drive or Ion Thruster is a fairly old development in space travel that shows a lot of promise. The basis of the current engine utilizes Xenon as a propellant. Basically, the inert gas is bombarded by an electrostatic charge, causing ions to be ejected at remarkable speeds. The future potential for this propulsion is exciting, and could lead to easier manned travel through space someday.
When I was writing The Guns of Mars, the Ion Drive was the main source of propulsion for the USS Plymouth, the spacecraft that ferried people from Earth to Mars. However, during the reviewing process, a friend of mine was dubious about the Ion Drive's speed and reliability, and thought it sounded downright boring. With a little discussion and creative revision, the Humboldt-Greyson Drive® was born, utilizing a more exciting albeit theoretical form of propulsion that utilizes unstable wormholes and hydrogen.
There are still some hurdles to making Ion Propulsion more commonplace and efficient. Current engine designs have a relatively short lifespan, but as I said the technology shows a lot of promise. Assuming we don't run into a new dark age, this sort of drive could take us on our next great forays into space exploration, and could pave the way for colonies on the moon, Mars, and beyond!
So, here's to Xenon. It sure is a noble gas.