Starting Out

Ok, so I just found out about this today so I'm a little late to the game.
I've already got a plan but depending on time I may have to cut bits, I'm working all this week.

So here's the basic idea: The Earth is under attack from aliens who've decided to try to bombard it with asteroids. In response scientists have shrunk the Earth and fitted it with rockets and coated the Moon in a layer of steel. The object of the game will be to maneuver the Earth in such a way as to affect the gravitational pull of the Moon. By swinging the Moon you'll be able to deflect the asteroids back at the aliens.

At this moment I can't decide whether this should continue forever and be score based or if it should be wave based. I'm thinking the former just due to time constraints though.