LEO is crowded enough (mostly with Starlink) that satellites have to actively maneuver to avoid collisions [1]. There's research [2] arguing that we're probably already in runaway territory in some orbits — that is, debris from 1 collision likely produces more than one secondary collision — we're just way over on the left of the hockey stick curve. A bit of bad luck, or two megaconstellations that don't perfectly coordinate their operations with each other, could move us to the right pretty quickly.
reply[1] https://arxiv.org/abs/2512.09643
[2] https://conference.sdo.esoc.esa.int/proceedings/sdc9/paper/3...
90% of starlink satellites are >400km in altitude. They aren't in very low earth orbits where that intuition even might be correct. They're above the space station.
replyI've definitely seen math done - though I'd have to dig it up again. I think in FAA filings.