This game has been the favorite for most of the camps I've used it in. I typically make it on Thursday. Most of the concepts in the game are pretty simple, the only sorta weird thing with the code is the way the asteroids get destroyed. Since scratch doesn't have a way to discern between different clones of an object using the "touching" block, when a missile hits an asteroid we create a new "explosion" sprite at the location of the missile. The asteroids, rather than looking to see if they're touching a missile, look to see if they're touching an explosion. This also has the cool side effect of allowing a single missile to potentially destroy two asteroids if they're close together.