Thank you for the feedback! Full-screen seems to be a common suggestion; I'm not sure how I would handle varying screen resolutions while keeping the game window size consistent. This and a mobile port would be an interesting challenge for the future. Thanks for playing!
which engine are you using? I use Unity and while not perfect it does a decent job of maintaining positioning of your game objects at varying resolutions (it's not perfect but it's good enough). For mobile I can definitely see using a finger pull motion to fire the asteroids as being a very intuitive feature/mechanic. I'm sure this would do so well on mobile.