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Fans of sci-fi and fringe tech may already be familiar with the idea of the "space elevator," which is pretty much exactly what it sounds like — and totally impossible with today's technology. But a pair of scientists think they've found an alternative: a Moon elevator. And it's slightly less insane... technically.
The idea of the space elevator, first explored in detail by Arthur C. Clarke in his novel "The Fountains of Paradise," is essentially a tower so tall it reaches space. Instead of launching ships and materials from the surface of the Earth to orbit, you just put them in the elevator of this tower and when they reach the top, somewhere about 26,000 miles up in geosynchronous orbit, they're already beyond gravity's pull, for all intents and purposes.
It's a fun idea, but the simple fact is that this tower would need to be so strong to support its own weight, and that of the counterweight at the far end, that no known material or even reasonably hypothetical one will do it. Not by a long shot. So the space elevator has remained well on the "fiction" side of science fiction since its first proposal. Hasn't stopped people from patenting it, though.
Source: https://techcrunch.com/2019/09/12/scientists-propose-spaceline-elevator-to-the-moon/
(Score: 3, Insightful) by qzm on Sunday September 15 2019, @10:11AM (8 children)
So, ALL you have to do to use this is get to geosync orbit?
You know, the bit that takes nearly all the energy anyway.. but from there to the moon, its easy?
Sorry guys, but you have solved the part of the problem that was not a problem (geosync to moon transfer), and done nothing to help the bit that IS a problem (surface to geosync).
Oh, and no, a space elevator does not need to support the 'weight of the counterweight', because the whole point is that that is in geosync orbit, but hey..
We DO have materials now strong enough, we dont have technology to make they in large enough quantities practically..
We also dont yet have heavy lift requirements large enough to make it a sensible development..
But hey, nice handwaving.
(Score: 2) by c0lo on Sunday September 15 2019, @10:18AM (3 children)
Strong enough for what?
For an anchored space elevator? If so, citation needed.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by Runaway1956 on Sunday September 15 2019, @11:19AM (1 child)
Well, carbon fiber shows promise. I'm not convinced that it's good enough yet, but it does show promise. GP did mention the minor little problem that we can't make it in the quantities needed, if it is strong enough.
(Score: 3, Informative) by Immerman on Sunday September 15 2019, @06:07PM
As I recall, multiwalled carbon nanotubes are the current leaders in tensile strength per unit weight - and they're just barely strong enough to support the weight of an optimal-cross-section cable extending 36,000km down from geosync orbit. I don't think carbon fiber quite makes the cut, though I'd welcome some counter-evidence.
But considering that you typically want at *least* a 10:1 human-safety margin even when building a normal elevator cable that won't lay waste to entire nations if it breaks and falls from orbit, just strong enough isn't really a viable option. And sadly, there's sound chemical reasons to assume that graphene is approaching the limits of tensile strength-to-weight ratios it's possible to make. The key factors being the strength of interatomic bonds, the number of bonds per atom, and the mass of the atoms being used. With the ability to form four extremely strong bonds, and an atomic mass of only 3amu per bond (well, 6 if you count both atoms involved), carbon stands as the prime candidate for extreme-strength materials. And while diamond thread may be stronger than graphene, it's probably not an order of magnitude moreso.
As I recall though, carbon fiber rope such as dyneema is already strong enough to make a "lunavator" with acceptable mechanical safety margins (ignoring impacts, effects of radiation, etc.), or a tumbling-cable "skyhook", which requires even less material. I'm not sure how just how much such rope is currently being made - but I suspect that for the immediate future at least the bottleneck would be getting it to orbit rather than making it.
Of course, most any orbital-based launch infrastructure really only starts making sense if you're building it from "native" materials, rather than hauling stuff up from the surface - and that's likely a long ways off.
(Score: 2) by HiThere on Sunday September 15 2019, @03:53PM
The only one that comes to mind for Earth is buckytubes...but you'd need really *long* buckytubes, and they couldn't carry much excess weight.
OTOH, on the Moon, Kevlar would be strong enough. I think it would work for Mars, too, though I'd need to check...but why bother when it won't be build this decade or next. (You need a lot of traffic to pay for the initial expense.)
There are lots of other skyhooks that, while they don't reduce the cost quite as much, are a lot easier to build, and don't have failure modes that are as extreme. My favorite is the pinwheel (rotating tethers with a heavy weight at the center). For that one you need to fly to the upper part of the stratosphere to catch your ride. And you'll need a (couple of) station-keeping engine(s)...probably an ion rocket (or so).
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 1, Insightful) by Anonymous Coward on Sunday September 15 2019, @10:27AM
Fully reusable rockets are much more important.
Space elevator is something you do in 100 years when you want 2 day free shipping to the Moon.
(Score: 4, Insightful) by Immerman on Sunday September 15 2019, @05:15PM (2 children)
I suspect the person writing the article misunderstood some key details. It's not possible for anything attached to the moon to be in "geosynchronous orbit" (aka match angular velocity with the Earth's surface), because the moon is not geosynchronous.
There is however a point where a cable extending down from the moon would match tangential speed (linear velocity) with the Earth's surface, which is where such proposed "lunavators" typically terminate - then you only need to reach sufficient altitude to grab on, with no horizontal acceleration necessary. And since the horizontal acceleration is what consumes the overwhelming majority of rocket propulsion, that could make a huge difference.
Also, a (beanstalk-style) space elevator *absolutely* has to support the weight of the counterweight. The counterweight is NOT in geosync orbit - it would provide no benefit there - it's well beyond geosync and spinning too fast for its orbital altitude, thus putting tension on the cable equal to the total effective weight of the cable below geosync. The chunk of cable passing through geosync doesn't provide any force in either direction, but it is the point where tension is at a maximum - all the cable above it is trying to "fall up" because it's rotating too fast for its orbit, while all the cable below is trying to fall down, because it's not rotating fast enough for its orbit.
(Score: 2) by qzm on Thursday September 19 2019, @05:34AM (1 child)
Sorry no, a 'beanstalk style' (which it is not, as it does not support from the ground, but hey I get what you mean) does not support the weight of the counterweight. It supports the weight of the cable.
You are right that the counterweight doesnt sit exactly at geosync, the mass average of the whole system does however. Generally it will be of high mass to provide inertial damping to the system, however the cable most certainly will NOT carry that whole 'weight', the weight it will see at peak is exactly the integrated weigh of the cable below geosync. The counterweight could mass 1000 times that, however that just means it is positioned closer to geosync to provide a suitable 'balance'.
So no, the counterweights 'weight' is not directly supported by the cable, as the mass is selected for inertial damping (due to wind effects on lower cable, mass of transfer vehicles, etc..). The cable must support its own 'weight' and nothing more.
That is still one hell of a load though..
(Score: 2) by Immerman on Thursday September 19 2019, @02:02PM
Tomayto , tomahto.
Remove the counterweight, and the whole cable falls to Earth. Remove the cable, and the counterweight goes flying off. They support each other.
I suppose it's not the counterweights "weight" exactly that's being balanced, rather it's mass and excessive angular momentum but "weight" starts being a lot fuzzier word when you start bringing orbital motion into the conversation.
Oh, and beanstalk space elevators are not supported from the ground - they couldn't be, the system would be far too unstable. "Beanstalk" simply refers to the class of space elevators where the lower end reaches the ground at all. As opposed to skyhooks, spacelines, etc. that typically never enter the atmosphere.