Ion engines aren’t strong enough to lift a rocket out of orbit, but once a ship is in space it would make the trip to Mars a hell of a lot faster.
Ion engines, on the other hand, accelerate electrically charged atoms, or ions, through an electric field, thereby pushing the spacecraft in the opposite direction. They provide much less thrust at a given moment than do chemical rockets, which means they can’t break free of the Earth’s gravity on their own. But once in space, they can give a continuous push for years, like a steady breeze at the back of a sailboat, accelerating gradually until they’re moving faster than chemical rockets.
If connected to an onboard nuclear reactor, an ion engine could propel a craft to mars in a mere 39 days, which would make the whole trip worthwhile. Of course, first they need to figure out how to put a nuclear reactor on a spaceship and also build an appropriately badass ion engine. But once they do that, we’re golden. [New Scientist via io9]