A National Aeronautics and Space Administration spacecraft named Dawn is making space exploration history — it is the first spacecraft to orbit two different solar system targets.

Plenty of spacecraft have flown by two or more planets or moons during their missions, but orbiting something is a lot harder.

The spacecraft has to put itself into “reverse” using its thrusters and lots of fuel in order to be captured by the gravity of a planet and go into orbit.

Otherwise, it would just fly right on by. And to leave orbit, it would have to pull itself out of the gravitational field using even more fuel, like hauling itself up out of a deep hole.

You can’t really put that much rocket fuel on a spacecraft. It would be too heavy and expensive to launch, but Dawn works very differently.

Dawn uses electricity to propel itself. Its ion propulsion technology shoots charged atoms, called ions, out of a small engine at super high speed.

The electrical energy comes from solar panels and the atoms are from a gas called xenon.

This technology has allowed Dawn to make its historic journey to the asteroid belt, first orbiting and studying the asteroid Vesta, then leaving that orbit, travelling another 900 million miles and going into orbit around dwarf planet Ceres.

Dawn is also the first spacecraft to visit a dwarf planet. The ion engine has enabled Dawn to spiral into the “gravity well” of one body, spiral back out, and have enough fuel left to go and do it all over again (although Dawn will not be leaving Ceres orbit).

Ion propulsion uses much less fuel than other means of space travel humans have tried.

Therefore, the spacecraft is light enough to launch, but still has the power to make big changes to its course.

The only real drawback is that it can’t accelerate very fast. In fact, it would take four whole days for Dawn to go from 0 to 60 miles per hour!

But once it gets going, it really gets going! By keeping these ion-powered engines thrusting for a long time, Dawn can do things no other craft has done!

• Visit Nasa’s Space Place to learn more about ion thrusters at http://spaceplace.nasa.gov/ion-balloons. Learn more about the Dawn mission at http://dawn.jpl.nasa.gov/