I had a real hard time with this one until I found out the upper right ledge ! Always stay on this ledge, shooting on your right to kill enemies that might appear, and you should do well. When a fuel tank appears, take it and go back to the ledge. Since the shuttle is just underneath the ledge, you will drop the fuel tank and get back to safety. The only enemies that might pose problems are the UFO's that target you (levels 6 and 12). They will get stuck under the ledge, but they can get you when you go out for a fuel tank. I found that going from this ledge to the left and continuing past the level to reappear to the right worked great with them, since they can't follow you. Always warp from left to right and they will have a hard time targeting you.