I like the concept you have going on here, but it can get really wonky. Once the ship hits an asteroid, I start flying to the ceiling and can't get back down, and sometimes I'll even start flying outside of the ship. After a few tries, though, I found out how to get to the turret, and it then just became a game of shooting all the asteroids.
If you continue to work on this, I think it would be a cool idea to turn this into a multiplayer experience, where you have one player on the bottom level controlling the movement, and the second player on the top level controlling the turret. Cool concept overall, and I think it'd be a cool game to continue expanding.