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Comment by olivermuty | Hacker News Reader

Put 29 988 people spread out on the globe (slightly larger since we are further out in the radius, but lets ignore that).

Do you still wonder? Probably you could put a few million up there before collision is a worry.

Space debris and blocking observatories is a much larger problem.

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> Put 29 988 people spread out on the globe...

... and then have them run at 17,000 miles per hour.

... on highly predictable and known paths.

Where only a percentage of objects can change their path if needed.

If a collision does happen 2 objects become 20,000 objects in an instance.

If a 300kg satellite at a 300 mile orbit becomes 20,000 pieces, those are pretty darn small pieces. Objects in space regularly get hit by <1cm micro-meteoroids. They may become disabled but they don't shatter. And by being so small their mass/area ratio becomes really small and they deorbit within 90 minutes from that altitude.

The orbital tracks at https://en.wikipedia.org/wiki/2009_satellite_collision clearly show how a high-speed collision can raise the orbits of the resulting debris, having imparted significant acceleration to them. (For example: <https://en.wikipedia.org/wiki/2009_satellite_collision#/medi...>)

That smash "created at least 1,000 pieces of debris larger than 10 cm (4 in)".

https://en.wikipedia.org/wiki/Satellite_collision lists six unintentional high-speed collisions involving satellites that have already occurred. That's with 2-8k or so in orbit at the time.

https://en.wikipedia.org/wiki/2009_satellite_collision alone made two thousand cataloguable fragments to track on new paths we didn't get to pick.

5 of those 6 were with debris. There is >500K pieces of debris in orbit bigger than 1cm in size, many of those in unknown orbits Adding 30K satellites in known orbits where debris cannot stay in orbit and required by law to have disposal plans before launch will not meaningfully change those odds.

Iridium 33 was active and capable of avoidance maneuvers. Both orbits were known. Despite this, they collided. It is clearly possible for this to get fucked up, and with 30k satellites in a shell, adding thousands of pieces of debris to the mix is clearly a non-zero risk. The exact magnitude of that risk may be debatable, but its existence cannot be waved away.

SpaceX's existing constellation (also in such a self-cleaning orbit) made 1,300 maneuvers in six months to avoid debris from a satellite explosion a year earlier. https://techcrunch.com/2023/07/10/starlink-satellites-are-do...

The risk of a collison is non-zero. The risk of Kessler from 30K satellites in a 300 mile orbit is zero.

Sorry, but that's simply false.

https://en.wikipedia.org/wiki/ASM-135_ASAT#1985_test destroyed a satellite at 345 miles. Debris from it persisted until 2004.

The low orbit reduces the long-term impact of such a chain-reaction - we wouldn't be locked out of space for a thousand years - but it would still be a serious disaster.

Only 8 pieces from that collision remained in orbit long term. All 8 were trackable and avoidable.

Just like Kosmos 2251 was.

Something still hit it.

Again, non-zero. You can argue it's low; you can't argue it's zero.

In the real world, infinitesimal is zero.

In the real world, we've had six satellite crashes, including at least one with basically the perfect mitigatable scenario; active satellite capable of avoidance, known orbits, large easily trackable objects.

There have been several notable collisions in the last decade. I think a full blown Kessler scenario is unlikely but it will definitely be a problem for satellite operators. Let alone the impacts on terrestrial astronomy.

are orbits (LEO, MEO, GEO) path-specific, like lanes, or it's willy-nilly where only altitude is mandatory-ish?

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