Good fun
Could do with a pause/options menu. Maybe a Difficulty select menu at the beggining?
Music toggle during gameplay.
Have you thought of introducing "aliens" into the flight between moons and give the rocket guns as well.
It also could really do with a objectives list.
There is large potencial for this game to be bigger with more missions.
Needs some replay value. Recording of time? High score list?
Maybe some easter eggs?