Nice idea, Katamari in space. I think you could have some UI or shader effect to show how close you are to objects, in Reizen I made "bullets" turn red the closer you get to them. It was just hard to judge distance and I'd often graze things I was trying to get. Maybe you could be a magnetic asteroid.
This points to an issue with how your camera is set up. Because the asteroid is in the center of the screen, it obstructs the objects you're trying to hit. So if you keep the camera angled so you can see what you want you end up going under it oftentimes.
I think this game could benefit from two views, a first person view, and a third person view. Could be a neat like, lowres space camera effect in first person. I dunno, maybe just try offsetting the camera. You should try 6DOF too, though players don't usually like that (see Egogia).
Tapping to move got a little better as I went on but I think it could be either less sensitive, or maybe just allow tapping forward to move camera-forward instead of on a flat plan, and space and ctrl won't be needed then.
I like the ending idea, I think it'll be really funny when you get an end screen saying how much damage you've done based on your size, how many people you've killed based on location, etc.
Maybe even, have the game be time-limited, so you gotta get big fast before NASA blows you out of the sky, maybe you can even go overtime and start dodging missiles while you get bigger, then you have to crash on missile launch sites, and a tiny part of you detaches to get big again. Could be a fun game-loop.
Your stars flicker like a motherfucker, I don't envy you, star shaders are cursed. I'd also play with the sense of scale a bit, the Earth shouldn't feel so small, but I get it needs to be arcade-y enough to be fun to collect stuff.