http://en.wikipedia.org/wiki/Ion_thruster Right now there\'s only 3 types of fuel, RCS, liquid, and solid boosters... but, you could make an engine that had extremely low thrust and fuel consumption. Match it so that say, the panels provide 1kw each, the engine uses 3kw, so you need 3 panels producing .000001 liquid fuel with an engine that burns .000003, providing some miniscule amount of thrust, and you don\'t 'break physics' too much. The only thing you can\'t replicate is the actual fuel metal used in an ion thruster, but that amount is tiny as well to the point it almost doesn\'t matter, especially in a game like this. There you go. After all, this is a game, and it\'s not really too much rocket science... this is best equated to the North Korean space program if anything... blows up significantly more than it accomplishes anything, etc etc.