Star Trek has changed the world. A space probe called Dawn is travelling beyond the orbit of Mars and heading into the asteroid belt between Mars and Jupiter. Dawn is supposed to achieve "standard orbit" (a Star Trek term - see picture) around the asteroid Vesta, staying and exploring a while then heading off to the asteroid Ceres later. These are two of the largest asteroids in this solar system. Why study asteroids? Well, the standard NASA answer is to gets some insights into how they formed and help scientists understand the formation of the solar system. Of course asteroids may be cholk-full of raw materials, so science may not be the only reason for such a trip.
This is not the first time asteroids or comets have been visited. On July 4th, 2005, NASA's Deep Impact probe intentionally collided with the comet Temple 1. In January 2006, NASA's Stardust probe returned samples of the Comet Wild and is on route to visit Temple 1 in 2011. In September 2008 the European Space Agency's Rosetta probe flew by the asteroid Steins.
But the Dawn visit is unique because it orbits two asteroids and if it had used conventional fuel it would have been too heavy to launch with current vehicles. Instead of conventional fuel Dawn uses Ion propulsion, a concept made popular during the original Star Trek series. This clip helps explain: