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).
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.
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.
How are you so sure, when scientist have been debating this for decades?
> Got it, altitude.
Quibbling isn't an argument.
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.)
[1] https://www.sciencedirect.com/science/article/pii/S092180092...
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'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're not wiping out LEO, but a particular LEO.
Certainly less dangerous than something "going the wrong way" in a given orbital shell, but not sure if it's completely negligible either.
But almost all the debris will either stay close to the original orbit or burn up within hours.
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.
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.
How many you can fit depends on the available technology. It should eventually be a lot more than 70K just in those low orbits... and still leave plenty of space for rocket launches and returns to thread their way in between them.
It is enough if it goes one round around. They can make a cascading effect which can destroy tens of satellites at once, and few fragments are enough. And closer to earth you are, less space there is. They can't all orbit on exactly the same level. There is always one which is on slightly higher level.
Humans are bad at intuiting exponents. There is roughly 200x more volume in LEO than there is between the ground and cruising altitude. Plane changes, moreover, take a lot of energy--you aren't going to get enough energy out of a collision to pollute nearby orbits.
There is no infinite space. The problem is exactly defining the number objects when that "small" amount of energy is actually enough to cause problems.
Straw man.
> problem is exactly defining the number objects when that "small" amount of energy is actually enough to cause problems
The exercise, maybe. The problem? No. In LEO, which is where Starlink orbits, there is no known solution for causing a Kessler cascade that causes more than a few billion in damage. Space isn't infinite, but it's really big.
Again, a few hundred thousand planes land every day [1]. They operate in a volume less than 1% that of LEO. To approach the object densities where we start controlling an airspace, you'd need tens of millions of objects in LEO alone. We simply do not have--not have any roadmap to having--the sort of launch capacity required to keep 30 million objects in LEO at a time.
There are real problems with more Starlinks in space. Kessler cascades are not one of them.
[1] https://www.travelandleisure.com/airlines-airports/number-of...
Space isn't infinite in the same way that 64 bit integers aren't infinite. Both are infinite for typical usecases.
Sure they can: Leading/trailing each other is quite common. Intersecting orbits are riskier, but also possible without inevitable collisions.
Another 500 km won't affect latency much. It'll be around 3 more ms per round trip.
radio bandwidth: higher frequencies travel a shorter distance and provide more bandwidth. so you get frequency contention and also you need your sats to be physically closer
latency: the further a sat is, the higher the latency. not an issue for text messages. a huge issue for phone calls and general internet tasks. the further you "push" your sat "back", the worst the user experience is
there's other issues too, like geostationary vs geosynchronous and coverage and exposure.
The further out you get, there's less atmospheric drag and each satellite is in view of the ground stations for longer but the cost of launch is higher and latency becomes a big issue. People expect 50ms latency for internet access not 500ms.
(Caveat: Not an expert by any means, just someone who had a similar question and did some reading, so my answer may well be incomplete or not fully correct.)
LEO maxes out ~ 1,200 miles radius, geostationary is at little over over 22,000 miles radius.
Because there isn't a problem. LEO contains more than 200x the volume of commercial airspace.
We run out of spectrum and launch capacity well before Kessler cascades become a problem.
I will again note that if Saber Tooth tigers had put things in the orbits we have, it would still be our problem.