I just replayed your game. You did a great job. It still has some bugs. However, you can fix it and add more things. :D
Thanks again for playing. I play-test the game so much that it's hard to know how diffiult it is for someone who is just starting. I fixed the bug with the upgrades. A couple of tips - stay away from the boundaries - it's easy to get "pinned down" when you're next to one. The exploding asteroids in level 5 are not a bug (read the intro to the level). On that level in particular it's important to shoot at asteroids from afar, if possible. You can also buy the "content sensor" upgrade. In addition to showing you how much gold, iron, and cobalt is inside of an asteroid, it will show a warning if it has gas inside, i.e. it explodes. The best upgrade, in my opinion, is the weapons upgrade. It gives you double-barrelled shooting so you can really kick some butt. Anyway, thanks again for playing and enjoy!