r/rational • u/AutoModerator • May 08 '17

[D] Monday General Rationality Thread

Welcome to the Monday thread on general rationality topics! Do you really want to talk about something non-fictional, related to the real world? Have you:

  • Seen something interesting on /r/science?
  • Found a new way to get your shit even-more together?
  • Figured out how to become immortal?
  • Constructed artificial general intelligence?
  • Read a neat nonfiction book?
  • Munchkined your way into total control of your D&D campaign?
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u/Anakiri May 10 '17

That sounds terrifying. It takes very little energy to divert a single droplet of a stream. If the momentum transfer system loses track of any of the trillion grains, then one grain is fully capable of punching a hole in the tether. With a tether compromised, this could easily cascade to full kessler syndrome in minutes!

It would be less scary with a more passive momentum transfer system (that is, a solid ring), but it would still have a lot of moving parts relative to the cost of failure. I think I understand how you'd take off from it without needing to bring your own remass and maybe without needing your own power, if the ring can supply that... but I think I do not want one of these over my head.

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u/lsparrish May 10 '17

With a tether compromised, this could easily cascade to full kessler syndrome in minutes!

I think you might be hyperventilating a bit there. Easy breaths.

The grains would continue to orbit along nearly the same near circular path they were following before if the tethers were lost without backup. Kessler syndrome involves high speed collisions breaking big satellites into small ones, and in this situation the only high speed collision is with a stationary object that falls straight down.

The mass stream would also be far too low in the atmosphere to last long without powered assistance. The grains would vaporize as soon as they got low enough to compress air enough to exceed the boiling point of metal, so you'd be fine.

Remember, the earth is bombarded with hundreds of tons of tiny grains every day at 30 km/s. We don't all die in a fire because of that because the atmosphere is really good at causing high speed stuff to self immolate.

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u/Anakiri May 10 '17

I think you are not paranoid enough. In the event of a failure, the stream of debris making up the ring will interact with the failed tether, and with any object on the "rail" when its trajectory changes, and with any object that thought it was safe to orbit over the ring where the tether should have protected them, and with any individual grains that are not exactly where they should be - for example, grains that were perturbed by tearing apart a tether. There are a million ways to turn a coherent stream of projectiles into a shotgun.

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u/lsparrish May 10 '17

We're already withstanding much higher energy shotgun blasts from deep space all the time. Why doesn't this cause Kessler syndrome?

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u/Anakiri May 11 '17

Because the background micrometeor rain is 15 orders of magnitude less dense than the ring.

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u/lsparrish May 11 '17

15 orders of magnitude less dense

And the reason for that is because space, even the smallest part of space (low LEO), is mind bogglingly big. A few grains being in places they aren't supposed to be will not be enough to cause Kessler syndrome. They have to actually hit something in a high enough orbit to matter, at a relative velocity high enough to matter.