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. The debris cannot physically move to higher orbits to affect other “normal” satellites, though it might impair launches.
Conversely, collisions at much higher geosynchronous orbits can’t possibly create a dense debris field as the total area is immense, deorbit will take millions of years, and everything is usually moving at the same speed (the synchronous part).
But all the bits the bits that end up with more energy than the orbit the satellites were on obviously do move up, and some bits will move up very substantially as we know from Mission Shakti debris: debris from that event at 300 km got apoapsis of up to ~2200 km.
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.
> there is always one which is on the highest level
Highest level?
> 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.
Certainly less dangerous than something "going the wrong way" in a given orbital shell, but not sure if it's completely negligible either.
There are other factors, too - imagine you're trying to send a penny around the entire equator of the earth, and think of the largest possible explosion you could subject it to without vaporizing it. A stick of dynamite could launch a penny only around a half mile's distance around the equator, assuming ideal conditions, which is about .0025% of the circumference of the earth, which is 10% of the distance between the earth and the moon, and the moon is about 25% of the distance from which earth's gravity stops being a significant factor.
If you carefully deployed a large number of well timed series of dynamite sticks precisely located so that each blew up perfectly beneath the penny at its apex following each previous explosion - you'd need 150-300 sticks to get the penny out past the edge of the effective gravitational well, the point at which other factors in the solar system have the dominant influence - it'd effectively leave earth and start falling toward the sun. At any point closer to earth than that, it will slowly and inexorably return back to earth, reaching up to 25,000 mph before vaporizing itself in the atmosphere (if it fell from the outer edge). If you had no atmosphere, a clear shot, and the "ideal" penny cannon to launch it, you could hypothetically reach escape velocity with only a quarter stick of dynamite.
Incidental bursts of gas, or even outright exploding objects in space are not going to launch a bunch of stuff into much deeper orbit. There's a constant downward pull, and gas and dust creating drag and downward acceleration the closer in you get, and just vast, incomprehensible distances to travel under the influences of gravity. Getting things to go faster than 25,000mph, or reaching escape velocity, without vaporizing the thing you're trying to make go fast, requires as big a continuous explosion as you can make over as long a time period as possible.
I love that AI can whip up an xkcd style "What-If?" type scenario for these questions.
