If you're the kind of person who follows me, you may know about the Kessler Syndrome.
That's when collisions between satellites and space junk create enough debris to cause *more* collisions, leading to a runaway chain reaction. This could render certain regions of near-Earth space unusable!
It's one of nature's ways of containing stupid civilizations. So don't be surprised:
A new study by Lewis and Kessler argues that we've hit the "runaway threshold" - the point where a chain reaction is expected - at nearly all altitudes between 520 and 1000 kilometers.
Below that, or above that, space could remain usable. So we could still get out and ruin other layers of space - or go to other planets and mess up those. Luckily, planned deployments of large satellite constellations like Starlink, Amazon's Project Kuiper, etc. will reduce the risk of such a breakout.
Yes, I'm joking - we can differ on whether the expansion of stupidity into the cosmos would be a good or bad thing compared to a mostly dead cosmos, and I don't really have an opinion on that. But the study is for real, and worth checking out:
• Hugh G. Lewis and Donald J. Kessler, Critical number of spacecraft in low Earth orbit: a new assessment of the stability of the orbital debris environment, https://conference.sdo.esoc.esa.int/proceedings/sdc9/paper/305/SDC9-paper305.pdf
Thanks to @michael_w_busch for pointing this out.
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In case you're curious: Lewis and Kessler say that if the population of objects in some zone exceeds the "unstable threshold", collisions will drive it up to some higher value, but that higher value could be stable. If it exceeds the "runaway threshold", it will keep growing indefinitely.
This is obviously based on some sort of simplification, since the paper says "if the number of intact objects exceeds the runaway threshold, the fragment population will run away over an infinite amount of time to an infinite number of fragments."
You can have larger and larger numbers of smaller and smaller fragments, but the model must not bother figuring out what happens when the fragments become molecule-sized. That's okay.
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@johncarlosbaez Thinking about your molecule limit. How small would fragments need to become to be classified as a 'metallic' atmosphere and it'll just be extra drag on satellites?
@ned @dean - alas, I don't know the answers. It would take work to extract them from the papers I've seen.
Currently, Wikipedia says
"although almost all debris objects (such as paint flecks) were lightweight, most of its mass was in debris about 1 kg or heavier."
and this is
"probably capable of catastrophically breaking up a 1,000 kg spacecraft if it strikes a high-density element in the spacecraft. In such a breakup, numerous fragments larger than 1 kg would be created".
I imagine it would take a long time for these fragments to be ground to fine dust.
@johncarlosbaez @ned @dean Not with that attitude! We just need to launch large amounts of sand blasting medium.../sarcasm
@kastope
One Kessler symdrome countermove I've seen is to shoot powder into reverse orbit, effectively being a "particle atmosphere". Since the smallest parts feel the drag the most, it would clear out paint specks and more or less leave GPS sats.
The powder suggested was confectioner's sugar.
@johncarlosbaez @ned @dean
@notsoloud @johncarlosbaez @ned @dean that's... strangely sustainable.
@notsoloud @johncarlosbaez @ned @dean Be neat if they used sugar rockets to launch it
@johncarlosbaez @ned @dean Even a paint fleck will destroy a heavy satellite, if it hits at a high-enough velocity. Given that some lightweight debris could be scattered in retrograde orbit, the resulting impact velocities could be enormous.
@shelldozer @johncarlosbaez @dean do you have a source for this?
Well before that point; solar radiation pressure runs up the eccentricity of dust grains and they fall out of the sky due to drag at perigee.
@dean @johncarlosbaez also, how small would it have to be to do no catastrophic damage to a functional piece of equipment?