HAHAHA Very cute game. Really impressive for your first original!
One point of improvement to consider is to limit the number of bullets visible in screen/set a cooldown (when you spam bullets, the game begins to get really laggy). Also, the cheat text is really small. I get this is to hide it, but I had a bit of trouble reading it (I just spammed my keyboard to find what letter it was referring to); you can make the font size a bit bigger. Lastly, the game does get redundant after you learn the cheat. Rather than several levels with marginally increasing difficulty, it would have been better to make only the last level unreasonably difficult to force the cheat. I imagine there would be people who won't play until the end bc all succeeding levels gets redundant after learning the cheats.
But overall, really awesome game! It was a blast! (pun intended)
Also, just a random note, but I just sat in my starting position while spam shooting missiles at the general direction of the satellites at the latter half of the game. It's a lot faster XD
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!