> For example, Starlink satellites orbit so low, that even if every single one of them collides and becomes dust, it will all decay and burn up in a matter of months, a couple years at most.
That is way too long. The threshold we are speaking of cannot allow any fragments, because they start chain reaction and destroy more satellites. And there is always one which is on the highest level. What if that gets destroyed?
> Kessler cascades are localised to specific orbits. In low-earth orbit, they're a problem for a few years.
> They're going to be annoying. But not catastrophic.
I think there is a misunderstanding about the whole term. If it is not a big problem, then it does not meet the definition. So there must be some threshold where they aren't problem. What is that threshold? Because certainly there isn't space for infinite amount of objects. Primary question is that whether that threshold matters on practice. If it is 70k, then it is certainly a problem, but who knows the exact number yet.
> Highest level?
There is always the one which is classified orbiting on the highest level in LEO. Also that object can get destroyed; which means it will start deorbiting and with a chance to hit some other object below.
Way beyond anything we can currently achieve with current and planned launch capacity or radio technology.
> that object can get destroyed; which means it will start deorbiting and with a chance to hit some other object below
Got it, altitude.
Yes, in theory. In practice, the odds of that happening are vanishingly low. If it did happen, the volumes we're talking about are still so big that you'd struggle to come up with a way to cause a third collision even if we remove satellites' abilities to marginally change their orbits.
> when scientist have been debating this for decades?
They have been. That's what I'm basing my arguments on.
You've been mentioning a ca. 70,000-bird limit. I think that comes from Bongers & Torres [1]. Their paper runs LEGEND (LEO-to-GEO Environment Debris Model). It does not distinguish between LEO and GEO. That's material because the natural decay period for an object in LEO is on the order of months to years, for LEO, to decades to centuries, for GEO.
Kessler in GEO? Real problem. If you wanted to be a space terrorist, you could probably engineer a cascade today that would make large sections of GEO unusuable for decades if not centuries. The point is that isn't possible for LEO, where you may make a mess in a few orbits for a few years at best.
> Quibbling isn't an argument
Sorry, wasn't quibbling. I genuinely couldn't tell what you meant by "highest level." (I was picturing a food chain, where big clouds of debris "eat" smaller satellites in their way.)
> If it is not a big problem, then it does not meet the definition.
It's still a big problem to wipe out low orbit, but it's not a long lasting one.
> What is that threshold? Because certainly there isn't space for infinite amount of objects.
Even if you crash a billion objects together at 300km, they're all going to go away in a few years. There is no threshold for semi-permanently ruining low orbit.
You can pack many, many satellites into the same orbit without any danger, for example – as long as they move in the same direction. Let's make it 1000 for this thought experiment.
On the other hand, just two moving in opposite directions are obviously going to crash.
So is the number of "safe satellites in all of LEO" 1000 or 1?
It purely depends of the density of objects. The whole definition of the Kessler syndrome is about the estimation when the density is too much to handle.
That is way too long. The threshold we are speaking of cannot allow any fragments, because they start chain reaction and destroy more satellites. And there is always one which is on the highest level. What if that gets destroyed?