First one was awesome. So is this one.
Love the defense missions, it's a nice break from mining.
Could you imagine taking this game to another level, say, where you have an opponent at another asteroid field and you can build factories, and the two of you send ships to each other's asteroid fields to try to destroy them? That would be pretty sick. Heck, even a mode where you could send out the ships against a computer-controlled asteroid field would be pretty neat.
At any rate, you've got my 5 stars. Keep turning out good stuff like this. :D