The bullet game objects do despawn after a while, but I found having them get destroyed too soon meant that you couldn't do long-distance trick shots from across the map (which gets bigger with every level).
The cheat text was in fact bigger at one stage, but like you said, I didn't want to make it too easy to find! But again, I'll agree that 15 levels for such a short-factor game was excessive, but I really wanted to ramp up the difficulty steadily, not immediately.
I'm glad you found the same technique as me though, the asteroid spawn range is always larger than the satellite spawn range, so generally staying in the middle of the maps give you a good view if you turn enough! Thanks for playing!