But as it gets cheaper to put new satellites up, cleanup gets cheaper too. And if access gets cheap enough I could easily see an international treaty mandating

But as it gets cheaper to put new satellites up, cleanup gets cheaper too. And if access gets cheap enough I could easily see an international treaty mandating that all satellites have an EOL burnup system installed. When 20kg costs $2mm a lot of people will balk at the idea. When 20kg costs $200k or $20k it's a lot easier to require people to include it. It could even be a bolt-on kind of thing, separately powered and controlled such that it doesn't have to be re-invented for every new satellite. Also with access being cheap enough we could start doing active cleanup, beyond just not making the problem worse. Aerogel is supposed to be great for capturing particles because it's basically frozen air. We could build a space-based aerogel factory and ship silicon ingots up which then get turned into aerogel panels to be used as replenishable armor for the factory. And once you have the factory up you just start making the area that the armor sweeps bigger and bigger. Build out sideways to clear a particular orbit faster, build up or down to clear orbits of various heights. It'd be insanely expensive right now, but if launch costs come down to $100/kg or $10/kg it starts to look reasonable.