Dawn III 
The Dawn spacecraft isn’t exactly a speedster. With its engines operating at maximum thrust, it would take about four days for the craft to accelerate from zero to 60. But what it lacks in horsepower, it makes up for in stamina — the engines can operate for years at a time, giving Dawn quite a push.
They’re about to push the craft away from its first target and toward the second, where it’ll arrive in early 2015.
Dawn has been orbiting the asteroid Vesta for the last year. It’s found that although Vesta’s only a few hundred miles in diameter, it’s put together like a planet, with layers of heavier material as you bore toward the center. Dawn also confirmed that several types of meteorites on Earth actually came from Vesta.
Now the craft is ready to head for the largest asteroid, Ceres. It’s about twice the diameter of Vesta. And unlike Vesta, which is quite dry, there’s some evidence that liquid water could lurk below the surface of Ceres. One of Dawn’s prime objectives is to look for that water.
To reach Ceres, Dawn will rely on three ion thrusters. Electricity from two large solar panels gives an electric charge to the craft’s xenon fuel. The thrusters then shoot out a stream of xenon ions — generating up to a third of an ounce of thrust.
If the thrusters do their job correctly, they’ll help put Dawn in the space history books — as the first craft ever to orbit two separate bodies in the solar system other than Earth.
Script by Damond Benningfield, Copyright 2012