After the release of my LD38 entry "Planetary Remains" I've played the game a bit myself and I realized that you can get past a critical spawn rate so the asteroids start blocking themselves. I did put a limit at the spawn rate but I was unable to test it out properly prior to release so I had to hope it was a reasonable rate. Still, I think the limit that does exist prevents total flooding of the screen so it should still be a <10 minute limit of how long you can play (I hope!)

Here is a video of my latest (successful) highscore attempt - I think the spawn rate hits the minimum cap at 3:52 in the video:

https://www.youtube.com/watch?v=posAWX45wfU

You can play the game here (HTML5 and Win download): https://ldjam.com/events/ludum-dare/38/planetary-remains