A propulsion device used in long-range space missions, generating its thrust by a beam of positive ions accelerated electrically.

The thrust is small (making such rocket unsuitable for launch from the ground), but the propulsion is very efficient, since the energy given to the ions comes from solar cells or a nuclear power source, and the acceleration can be maintained for quite some time.

Because of the separate power source, the energy each ion gets is more than the energy given to molecules in the jet of ordinary chemical rockets, which is limited by what the chemistry of the rocket fuel provides.