> especially with all the stuff that SpaceX has put into orbit in recent years
I've heard this repeated a lot but I've never seen anyone do the maths. StarLink satellites are all in very low orbits, so intuitively it seems like most debris from a collision would just end up deorbiting.
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.
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.
I've definitely seen math done - though I'd have to dig it up again. I think in FAA filings.
The best sources that I can find say that Starlink sats orbit around 550 km above Earth. By all accounts, this distance is well within Low Earth Orbit definitions. However, you used the term "very low earth orbits". I never heard before and needed to research it. It is a neologism from 2017 and does not seem to have a precise definition. Most uses indicate less than 450 km above Earth.
The International Space Station flies around 400 km above Earth.
I've heard this repeated a lot but I've never seen anyone do the maths. StarLink satellites are all in very low orbits, so intuitively it seems like most debris from a collision would just end up deorbiting.