Engine lowers cost of getting into space
The trick is that, once in space, the engine uses solar cells, letting it take off with 40% less fuel, and the exhaust is fine-tuned to get more thrust. The last point means controllers on the ground can throttle the engine, so it needn't run at maximum thrust all the time, as do most rocket engines on satellites.
In the ion propulsion engine, xenon atoms are injected into a discharge chamber where they are stripped of their electrons and turned into ions. Light electrons are held back by a magnetic field, while heavier ones are accelerated out the back end by an electric field, generating thrust. The electric and magnetic fields generated are the mediating forces in controlling how much thrust the engine creates.