Space Elevators Face Wobble Problem

NewScientist is reporting that while the strength of the tether has long been considered the main problem in building a space elevator, a new study suggests that a dangerous wobbling problem may also be a serious obstacle. "Previous studies have noted that gravitational tugs from the Moon and Sun, as well as pressure from gusts of solar wind, would shake the tether. That could potentially make it veer into space traffic, including satellites and bits of space debris. A collision could cut the tether and wreck the space elevator."

Comments

Of course it's not easy

[TheCoders]

I don't think anybody really thought building a space elevator would be as simple as reeling out some cable and strapping on a cabin. There are a million complications, even before we get to solar winds or tidal pulls. How about something as simple as airplane traffic? Birds? Squirrels, for goodness sake!?

Plus a million things we haven't thought of, and won't think of until the product is built. When train tracks were first laid down, they were too close together, because nobody had heard of the Bernoulli effect. Trains were getting slammed against each-other by their own created air pressure. What did people do? They learned from it, and moved the tracks further apart. We take trains for granted, but they were not without their technological hurdles to overcome.

Of course something like a space elevator is not an easy accomplishment. Does that mean we shouldn't try?

What do you think?

Re:Of course it's not easy

[Gat0r30y]

Of course something like a space elevator is not an easy accomplishment. Does that mean we shouldn't try? I think we should and probably will at least give it a shot. Also, as you note, there are a LOT of complications. Complications I look forward to seeing innovative and cool solutions to. First and foremost though, we gotta get the material engineering issue solved, until we have a material which can withstand the forces involved, were stuck with regular elevators. Nanotubes look promising, and this gives us an excuse to invest in the research.

"I think" Engineering

[iamlucky13]

.But Perek says that may not be enough. "Previous proposals for a passive tether controlled from the ground do not seem stable to me," he told New Scientist. Anders Jorgensen of the New Mexico Institute of Mining and Technology in Socorro, US, who has previously studied the problem, agrees that stability is a concern for space elevators. But he says the new paper does not provide a quantitative analysis of the issue, and is not convinced that thrusters would be needed to stabilize the cables.

Basically, the problem has been noted before this Perek guy's paper, but not studied in any detail. Perek reiterates and perhaps expands upon the concern, but doesn't do any analysis to establish the actual likelihood of a problem. It's basically an opinion.

Atmospheric oscillations should be extremely well damped by drag. Oscillations due to gravity from the sun and moon may be a greater concern, because there is no drag, although including conductive paths in the cable may allow the earth's magnetic field to suitably damp the oscillations.

An IEEE article on the topic discussed the related issue of harmonics. If these oscillations propogate through the cable at a rate that syncs up well with the rotation of the earth, gravity of either the moon or sun may amplify them. The tensile component can be tuned by adjusted the mass and tensile stiffness of the cable, and even better, the mass of the counterweight, allowing you to tune it by changing the tension, like an incredibly huge guitar string. The will also be a pendulum like motion due to the fact that the earth is on a tilted axis. This seems to be the concern discussed in the article.

I personally am not at all convinced that oscillation of the cable alone (waves) is a problem due to it's low density, but oscillation of the combined cable and counterweight (pendulum) may be. If so, thrusters on the counterweight are much simpler to attach and refuel than they would be at intermediate altitudes on the cable.

wreck the elevator

[alta]

Looking at the sheer size of this, I'd say that 'wreck the elevator' is a major understatement. Look at all the other stuff that would be wrecked. I remember reading a Ben Bova book a while back where terrorists sabotaged an elevator. They went to the top and severed the connection to the counterweight. The rest of the thing toppled like a flimsy tree, wrapping itself 1/2 way around the earth. Yeah, scifi, but it could happen.

Re:wreck the elevator

[merreborn]

Actually, no. The rotation of the earth would cause the ribbon to wrap around the earth in an easterly direction

If what you propose were true, a pin balanced on its end would always fall over to the east as well, as would a perfectly symmetrical tree, or a falling skyscraper.

They don't, because all these things, a space elevator included, travel through space at the same speed as the earth's rotation. Why would it suddenly, magically lose that momentum, were it severed from its counterweight?