The world needs a new source of energy, an unspillable source.

Question on Twin Ion Engines?

You might remember “twin ion engines” from Star Wars (though you probably don’t). Apparently NASA has actually developed TIEs. These engines don’t travel nearly as fast as in the movie though. They use mercury ions and solar power for propulsion. I don’t understand how this is possible. Normal rocket engines are able to propel themselves in space through impulse, that is, by accelerating the mass of the fuel to a very high velocity in a short time. But with twin ion engines, where does the mass come from? They can accumulate energy through solar panels but not mass. It would seem that once the ship has no mass to accelerate, it could have all the energy in the world and not be able to change it’s direction or velocity.

Any Ideas?