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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: 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.