Interesting gameplay, I don't know if it was so planned, but I decided to fly back to the earth, and I was destroyed by asteroid - it was funny :)
Anyway, one point would be great - I think 'S' for shooting lexically passes, but I think here you can remap this control - probably to enter. I have programmed earlier game engine on C++ for my practical work in bachelor with a representation of old Konami game Scramble - and there I have mapped Enter/Space for basic shooting