What about space debris? If we build such a large stucture up to the geostationary orbit, won't it be exposed and how can it be protected? The top station can't dodge - or can it?
One interesting aspect of the space elevator remains its failure modes though. Cable failure, for any reason, is going to be a problem. We'll need a safety concept both for the ground as well as the payload if humans are going up there. I hope this isn't going to be one of these things where everybody ends up agreeing that it's not feasible to save lives in the event of catastrophic failures.
Edit: VLM does have a point in that a falling cable might be a problem on Mars. The moon doesn't have enough rotation for a fixed skyhook (space elevator) anyway. :-) More advanced rotating elevators in a moon orbit, maybe. But it might be hard because of the moon mascons (the moon is lumpy internally with different density, which results in gravitational anomalies).
The moon doesn't have enough rotation for a fixed skyhook (space elevator) anyway.
You're just fairly restricted in where you can put it- you can only put one near the sub-Earth and anti-Earth points, such that the cable passes through the L1 or L2 Lagrange points, rather than anywhere along the equator. The cable would have to much, much longer than for a space elevator on Earth, but the Moon's lower gravity actually makes the engineering challenges Not As Bad- i.e., we could build a lunar space elevator with current materials.
On the moon, an electric rail launcher with 5-10G only needs to be a few km long.
(Iirc, 1G acceleration of four minutes is the launch velocity of the moon? ~ 2.4 km/s.)
Edit: This assumes local materials for the electric launcher. If everything is skipped from Earth, it might be different. But, consider -- if you need to launch so much stuff from the moon, you must already have the infrastructure to build things there.
Think about it... without a working active stabilization system and a carefully engineered for re-entry shape, "stuff" that re-enters usually doesn't make it very far in the atmosphere before being turned into dust.
We have a long way to go until an elevator can be as large as a dino-killer asteroid. Existing designs have spectacular surface are to volume ratios, there won't be much left...
This is, however, a very serious problem on the moon or perhaps mars. And because the moon's gravity is so low compared to the earth, we're almost certain to have elevators all over the moon before the first one on the earth. A moon-vator is so small and light we don't even need new tech to pull it off, just drop a couple billion and we can do it within perhaps 3 years if done privately. Maybe 30 if NASA runs it.
So yeah, its a problem, but not for legacy earthlings.
That said, I've got to imagine that bottom .1% of the cable will be made differently to counteract all the water and oxygen around it.
Lightning might be interesting but wind is no big deal.
What about lightning though? When a cloud contains an imbalance of electrons, won't the lightning strike much rather travel through the cable and weaken the material so it breaks?
Yes, but the actual continuous power delivered by it would be surprisingly low, making it pointless.
> And, would stopping lightning cause other problems for Earth?
No, as the effect would be very localized.
We have commercial experience (well, at least in Russia) making communications towers a mile or so tall. Making one five miles tall would not be a huge stretch of the imagination, and those are fairly tolerant of all kinds of ridiculous abuse. Simply attach the elevator at the top of the tower instead of ground level and you've eliminate pretty much any man-portable non nuke attack potential and most mechanized vehicle attacks (or accidents).
Ditto the elevator material. We can't afford for weight reasons to make the entire thing "airliner proof" but we can afford to make the bottom 10 miles or so "small cessna proof". So make the bottom couple miles quadruple redundant steel battleship anchor chain or whatever. 99% of it will still have to be light as a feather, but nothing can hit it, so thats OK.