"Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space."

(RIP Douglas Adams)

Space is hugely, vastly, mind-bogglingly big.

Useful low orbital shells around the Earth are an awful lot smaller. They're still big, like the sky is big, but airplanes do manage to, at least somewhat regularly, collide with each other "in the middle of nowhere" (most midairs are around airports, since there are a lot of airplanes heading in and out of them).

Aircraft debris, however, falls out of the sky in short order. Orbital debris doesn't.

The probability of an initial collision is fairly low, but once you have a few, or someone decides to show off their new ASAT weaponry (which is functionally a satellite collision, just one of them only having been in space for a short while), you now have flak that won't go away, moving in all directions at orbital velocity. That, then, has the potential to start causing all sorts of problems, and once that's taken out a few more satellites with orbital-energy impacts, you start having a real problem.

Will it happen? Those invested in littering certain useful orbital shells with satellites claim not. We'll see.

Kessler syndrome is definitely a problem.

I've heard SpaceX claims to deal with it by putting their satellites in an orbit that requires periodic boosting to stay put -- if they don't, satellites decay and de-orbit after a few years.

The plan is, I think, to regularly retire (de-orbit) and replace these satellites so they can continuously improve the design, and as a nice side-effect any collisions or otherwise misbehaving objects will at least stop being a problem after a known maximum span of time.

Another benefit is latency

And the birthday problem applies; the probability of a collision goes up quadratically. If you have N objects, you've got N^2/2 pairs that could collide.

Low earth orbit (where Starlink and the ISS are) actually has a fair amount of atmospheric drag. Random google searching suggests an inert Starlink satellite (or fragments of one) would come down in 5-10 years.

That's the claim made, yes.

Now, how many other satellites are likely to get hit in "5-10 years" of flak flying around at orbital velocities? It's nice if your goal is to say "Well, it probably won't render space useless forever..." - but that assumes one collision, and no ongoing collisions. If it's "5-10 years per collision," and each new one resets the 5-10 years timeframe, well, there's a lot of stuff up there that can make a mess.

Unfortunately, the low orbital shells are also "everywhere." It's not like geosync orbits where if you Kessler them, well... not going to have geosync stuff anymore, but you can still use other orbits. If you Kessler LEO shells, you pretty much have a high risk of anything you try to send to space getting blasted on the way up. It doesn't take much of a bit of debris, at orbital speeds, to trash your booster and make you have a bad day. I guarantee a bolt at 17,000 mph will do some damage (typical LEO velocities) - that's about ~22x the speed of sound in the atmosphere, depending on altitude.

If there are tens of thousands of things up there and you start things colliding and blowing up, you've basically put a defensive shell around the earth for a century, if not longer, by the time all the satellites get fragged and the debris eventually comes down.

> If it's "5-10 years per collision," and each new one resets the 5-10 years timeframe

It's not.

The concern is that unwanted collisions will become common enough that satellites break down or are completely destroyed within months. There will never be enough debris that we can't fly through LEO.

> There will never be enough debris that we can't fly through LEO.

Flying through and flying through safely are very different things. With tens of thousands of objects in and below LEO and (presumably) increasing flights to orbit, it's only a matter of time until a rocket gets taken down. It doesn't require a particularly large piece for an involuntary update to your deorbiting plans.

Therein lies the birthday paradox: the frequency of collisions among n bodies grows quadratically; but the probability of a one-time passerby being involved in those collisions only grows linearly.

Yes, space is big. Lower earth orbit is still very big. However if you have dozens of operators, each with thousands of satiates making multiple round the world trips. The chances of a specific satellite colliding perhaps is tiny (given how big space is). However the chances of one of the thousands colliding with any of the other thousands over any of their orbital periods increases exponentially as the number of satellites increases.

Tens of thousands.

> There are currently over 1,600 Starlink satellites in orbit, and that number will continue to grow; SpaceX has filed paperwork for up to 42,000 satellites for the constellation.

https://www.space.com/spacex-starlink-internet-satellites-la...

They're aware of the risk of collisions, but toss in a few more vendors trying for the same size, and you can have potentially hundreds of thousands of satellites in the shells. They're big, but they're not that big.

What worries me personally is that they are aware and simply don’t care. Our current climate catastrophe is a testament that big business can be completely aware of an impending disaster, but still ignore it while profits are showing.

Since space debris in the satellite zone is already a problem, that's not a solution.

There isn't just one satellite zone. Starlink satellites are about 4 times closer to earth than than they are to the geosynchronous Hughesnet satellites. The starlink satellites are close enough that even after full Gravity-style Kessler syndrome, you could just wait several years and start over from scratch.

Obviously that is something to avoid, but it's not like we're filling up a non-renewable resource in low earth orbit. It cleans itself naturally.

Note: Starlink orbits at an altitude of 340-350 miles . Hughesnet’s geosynchronous orbit has an altitude of 22,000 miles. That is over 62 times higher, not 4.

FWIW.

I apologize, you are quite correct! Not quite sure what my brain was doing there, I was looking at those same numbers and somehow typed 4.

Sorry if this a stupid question, but in the event of mass collisions a la Kessler, wouldn't some percentage of the debris get stuck in higher orbits? The kinetic force of collisions at those speeds seems pretty significant.

personal opinion, space is huge, and the gap between companies issuing press release and the number of companies actually implementing hardware is huge.

oneweb is just now becoming barely usable above 55 degrees north latitude. they have a lot of launches to go before it's anything like a real network (and will not be for individual end user CPEs, a oneweb terminal is much bigger and more costly). other things like telesat LEO network remain in the land of vaporware, same as with amazon's.

So is the earth, really. Reminds me of how all humans would fit in a ball of meat in Central Park [0]. The satellites aren't much bigger than humans, so even if there was a starlink satellite for every single human, it would still barely make a dent. Let alone the fact that the surface area would be larger 2000KM up, and without oceans.

[0] https://www.reddit.com/r/theydidthemath/comments/p0qws3/self...

Nit, but 550km up. You can visualize the Earth as a basketball with the Starlink satellites crawling around an inch above the surface. (Now, with my local folk out of the way, the rest of you can visualize a football with the satellites 2cm over the surface.)

This reminds me of my favorite "true but hard to believe" fact.

Imagine you have a string wrapped tightly around the earth, how much more string to you need to raise the string 10cm above the ground everywhere? The answer just feels so hard to believe, but it indeed only depends on pi and 10cm.

For someone like me, who's ability to do math stops when they run out of fingers and toes, what's the answer?

2pi multiplied by how much you want to raise the string, I believe: https://en.wikipedia.org/wiki/String_girdling_Earth

Do you have a list of these? I'm aware of Amazon's Kuiper and also ViaSat / OneWeb. Neither are available yet.

Yes, they have a plan to deal with collisions.

There's not dozens for broadband internet. A lot more if you count companies intending to build low throughput non realtime m2m data networks with cubesat size things.

Announced but not implemented Leo other than SpaceX include amazon, Russia, china, telesat.

The phrase you are looking for is "Kessler cascade"