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Space Elevator

(neal.fun)
1773 points kaonwarb | 3 comments | | HN request time: 0.602s | source
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tempestn ◴[] No.45640679[source]
TIL it's estimated that over 48 tons of meteors hit the atmosphere every day.

Regarding actual space elevators though, while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible - they're still pretty firmly in the realm of sci-fi. We don't have anything close to a cable that could sustain its own weight, let alone that of whatever is being elevated. Plus, how do you stabilize the cable and lifter in the atmosphere?

A space elevator on the moon is much more feasible: less gravity, slow rotation, no atmosphere, less dangerous debris. But it's also much less useful.

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tsimionescu ◴[] No.45641725[source]
While a space elevator doesn't contradict any fundamental limits of physics, that doesn't mean it's actually possible to build one. There is no reason to be certain that it's actually possible to create a material that has the required characteristics in terms of tensile strength to support it's own weight, plus the weight of the elevator, plus the weight of all the additional cabling. It also has to endure the huge temperature differences that it will experience along its length and from day to night and from season to season.

This is especially true considering that you don't need something that barely holds - you need something that you know will hold up to many times more weight than it needs to, so that it can be safe: the potential energy such a thing would store would be enough to dig into hundreds of meters of rock all around the world, if it ever crashed. So, you have to ensure there is no realistic chance of it ever crashing. It also has to be highly non-fragile in other ways, so that a madman with a bomb or a freak collision with an airplane or a meteor (especially likely in the thin upper layers of the atmosphere) won't bring it all down.

This combination of properties may well be completely impossible to actually achieve in a material. Even if there is no obvious basic law of physics that it would break, that doesn't mean that it wouldn't break other, harder to touch, derived laws.

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icetank ◴[] No.45642412[source]
The issue of the line falling back to earth is solved by putting the base of the elevator on water. If the top part of the elevator was cut of you could even detonate charges along the line to make sure all pieces fall into water.
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tsimionescu ◴[] No.45647151[source]
I don't understand why you think that where you put the base of a 35000km cable makes a difference for where the rest of it would fall. I also don't understand why you think that a 35000 km long cable falling in the ocean from space would cause any less damage to the planet than it falling down on solid ground, or at least why the difference would be significant.
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1. JumpCrisscross ◴[] No.45647685[source]
> why you think that a 35000 km long cable falling in the ocean from space would cause any less damage to the planet than it falling down on solid ground

They’re not obviously wrong.

A lot of the cable is moving at escape and orbital velocities. Tensile strength is all that holds it together.

If, as the cable fails, you sever the parts above from below around escape velocity, you’ll significantly reduce the length of cable that will ever hit the surface.

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2. cfraenkel ◴[] No.45650555[source]
Orbital and escape velocities??? The elevator is sitting over a stationary spot... it's moving at earth's rotational velocity. Only the portion above the GEO anchor is moving at orbital velocity.
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3. LorenPechtel ◴[] No.45652656[source]
But it has altitude. The stuff that's low down doesn't have a lot of orbital velocity, blow the cable and it falls nearby. And the stuff far away has enough velocity that it goes into a very eccentric orbit rather than hitting the atmosphere.

Just because it's moving below circular orbital speed doesn't mean the periapsis is in the atmosphere.