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Space Elevator

(neal.fun)
1773 points kaonwarb | 4 comments | | HN request time: 0s | 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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1. 0xEF ◴[] No.45642456[source]
Are we to assume they would be falling straight down? Because I'm pretty sure that's wrong. I'm not a physicist, though, and am happy to be corrected because every time the Space Elevator comes up, I want to know what happens when catastrophic failure occurs and how we'd mitigate that.
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2. speed_spread ◴[] No.45642691[source]
It would become a giant whip falling faster and faster round the equator.
3. devilsdata ◴[] No.45648787[source]
https://en.wikipedia.org/wiki/Space_elevator

> Above GEO, the centrifugal force is stronger than gravity, causing objects attached to the cable there to pull upward on it. [...] On the cable below geostationary orbit, downward gravity would be greater than the upward centrifugal force, so the apparent gravity would pull objects attached to the cable downward.

So, without defensive countermeasures, the Space Elevator would indeed whip around the Earth.

But honestly, if I were designing such a thing, it would have break points, and maybe even a whinch at the base, to pull the line in. I'd also build it over water, and not over a population centre.

But I'm only a software engineer– it's likely a lot more challenging than this.

4. LorenPechtel ◴[] No.45652642[source]
If you blow the cable apart at a few important points the mass that falls either hits fairly near downrange from the tether, or does not hit at all. Have a group of range safety officers for the charges and a law that when on duty they are expected to shoot any politician that contacts them. (I'm thinking of Fukushima. We need to vent the reactor or it will blow! You can't vent until the city has been evacuated. The reactor didn't listen to the politicians.)