While it is a good concept...
there doesnt seem to be any strategy at all. Just place whatever ships you can evenly around earth and you win. (you will seriously have so many ships its like a wall of deadly metal around earth)
Missile ships are worthless because they damage your own ships, the way ships get pushed around by the asteroids is stupid especially since the SHIPS cant fly back into place, good idea but poorly executed.
I would enjoy a sequel if these things were corrected