mirrorshard: (Default)
[personal profile] mirrorshard
Oh, dear. People are still talking about space elevators? The state of science teaching these days... (sparked off by comments to this post by Charlie Stross)



You can't build up to geosynchronous orbit. You can't build to within orders of magnitude of it. You can't dangle a rope that far, even if you're one of the less brain-witheringly stupid of the people suggesting it and realise you need to work in both directions at once to keep the centre of mass at the geosynchronous point.

It's not a matter of super-strong materials. The theoretical strength of a molecular chain, one atom thick, is the strength of the interatomic bonds. As you add more strands, you get diminishing return from each one. If you stop pulling along the length of the interatomic bonds, and start pulling sideways or at an angle - which will inevitably happen when you start making cables or ropes out of them - then you're relying on the intermolecular bonds instead, which are much weaker.

In addition, the stresses are not going to be purely vertical, so your straight-line calculations are out the window. There will be some extremely nontrivial bending and torsion stresses as well, and quite a few impacts to be taken into account. Even assuming your super-strong material is also super-stiff and not brittle, your engineering is still in rather more trouble than merely attempting to dangle a thirty-five-thousand kilometre long cable would suggest.

Yes, you say, but you forget the indomitable spirit of humanity. We'll keep on making better materials.

You Can't Get There From Here.

What you want means fucking around with either fundamental particles, the forces of electromagnetic interaction, or basic geometry. If you think we're going to let you do that on our planet, you've got another think coming.

Even if you get around the engineering problems, imagine the legal ones. Who's going to let you do that in their country, near their citizens? We're talking here about people who object bitterly to wind turbines and mobile phone masts.



If you're going to start assuming new and interesting kinds of physics, go for tractor/pressor beams instead. It's no less implausible. Build seventy thousand aerowhatsits with spatial awareness and station-keeping ability, and make them link themselves together in a rigid structure with your shiny new docsmith gear, then climb up them from one to the next. Basic geometry and packet-routing algorithms mean that if you do it right, the structure can lose a fair number of its nodes and still both remain rigid and give you a path along it. In addition, failed nodes can fall out, or be swapped out, without very much KE hitting the ground at any one time as a result.

You'll still need to work out how to keep them and the climbers all fuelled up (ideally, route power through the lattice from PV arrays along its length, preferably without frying birds along the way, and let the climber leech as it goes) but most of the objections to the classic model have been solved.

Of course, there remains that pesky super-science to deal with.
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