Calling the Space Elevator

CornfedPig writes "SPACE.com has an article that suggests building an elevator to a 100,000 km-high penthouse could be possible within the next few years at a cost of about $5B US. Widespread availability of low-cost carbon nanotubes appears to be the gating factor. Existence of such an elevator could drop the cost of lifting things (satellites, people, CowboyNeal) into orbit to a couple of hundred dollars a pound. Anyone remember Clarke's The Fountains of Paradise?" Space elevator stories come along every few months; we never seem to be getting any closer to actually doing it. I imagine it will happen at some point in my lifetime, but...

The flesh is willing but the fiber weak

[WolfWithoutAClause]

Ok, I admit it, I submitted the slashdot story before last on this topic, and I linked to the same paper that was mentioned in the next story, and this article is a piece on the same guy who wrote the same paper.

Technically, the bottom line is:

No we can't do this right now. The fibers aren't strong enough to do this without bankrupting the global economy. An exponentially tapering fiber can theoretically do this at any time, but it would be wayyyyyy too big and heavy to install. (e.g. a steel cable would be ~hundred meters wide at the thickest point, and >38000km long...)

For the suggested construction technique, the carbon 'rope' needs to be able to give 72.5 Gpa strength, plus safety factor (typically 2). A single fiber gives about 73 Gpa right now. So we've no safety factor at all... but:

Joining the individual fibers together- nobody has done this whilst maintaining enough of the strength. Splicing normally soaks up 15-30% of the strength, and so we're now 15-30% down on the required strength, and nobody has even managed to do splices this good with carbon fiber.

Only a little percentage off then, but this pushes the mass up incredibly when you do the maths.

Still, we're very close. 3 reasonably simple(?) breakthroughs (one to gain strength, one to splice the rope, one to actually scale up production from one 3cm fiber to trillions of 3cm fibers in a reasonable time) and we're saying 'Hi!' to the rest of the solar system.

Re:There's a reason we don't build them

[WolfWithoutAClause]

No, the theory is sound, the initial fiber would only weigh 20 tonnes, if you can achieve the necessary strength which right now we are a smidgen short of. The cable is very thin and flexes easily, so the lunar tidal forces are no problem. The paper says it would be built on an oil rig type structure on the equator, well away from dry land, so NIMBY is obviated.

Voltages? I don't think anyone knows what would happen with that, as far as I know it wasn't mentioned in the original paper either. It might be soluble. Lightning strikes could spoil your whole day that's for sure.

Re:There's a reason we don't build them

[Thellan]

I have read the same paper you talked about in your previous post. The writer does mention lightning strikes and discusses a few solutions.

One solution is that the place where he proposes building it has on average 3-4 lighting strikes per year which is the lowest in the world. It also has the lowest number of storms in the world per year. Also, ocean currents make a sort of tidal pool area and hurricanes do not go into this section of the Pacific.

Another nice thing about the design is that it will not be nearly as destructive as what everyone thinks of when they mention falling space elevators. One of the requirements for the glue for splicing the nanotubes is that it have a melting point that is below the heat experienced in re-entry. This means that all of the re-entering elevator except for the lower 60 to 100 miles of it will break up into little pieces each less than 10 cm in length and they will burn up on re-entry. The 60 to 100 miles that does not will fall into some of the emptiest ocean in the world.

Also, to deal with winds, the shape of the cable is a cresent shape designed to face into the wind so that it does not flutter.

As Mr. Clarke says "A space elevator will be built 20 years after everyone stops laughing."
I'm not laughing, are you?

Re:There's a reason we don't build them

[Yarn]

'Buckytubes' (I hate that name) are within an order of magnitude of the strength required.

The suggested building method is to put a bulky object (eg captured asteroid) in geosync orbit and lower the cable down, moving the 'roid back up slowly to ensure the centre of mass remains geosync.

How thick do you think this thing'll be? I think that it *not* being visable is going to be a larger problem. ISTR that the core will only be of the order of a few centimetres diameter, you'd not see it at 100m, hardly a problem across "much of the Earth's surface"

Voltage potential? You think the Earth circles the Sun because we're +ve and it's -ve? The only real issue would be a conductor moving through the Earth's magnetic field.

You should call yourself PhysicsTroll, not PhysicsGenius...

Hypersonic Tethers will come first

[Mad Bad Rabbit]

As other posters have noted, we don't have any
materials strong enough for an elevator all the
way to geosynchronous orbit, so it's a bit too
soon for anyone to claim we could build one in
the next 10 years.

HOWEVER, we do have materials strong enough for
a "hypersonic tether". This'd be a much shorter
tether, only a few thousand km long, and moving
at a good clip around the Earth, with the lower
end just above the atmosphere.

With this in place, you could use cheap sounding
rockets, just barely capable of making it out of
the atmosphere, to rendezvous with the tether as
it swept past. The cargo would be grabbed by the
tether and snatched up into low orbit, while the
sounding rocket fell back to Earth.

There aren't any good online references, but you
can find USENET discussions of the technology on
Google Groups, keywords "hypersonic tether".