Sure! It is intuitive (IMHO), when space ship has thruster - moving forward should be direction from thruster (like W on keyboard) and rotation should be used to change direction. That scheme was used many times. In your game, ship moves the direction you press equivalently, which ignores the fact that thruser is behind:) I assume, that UFO can fly all directions (it is round, and it is UFO, after all). Just friendly comment and my perception:)