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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."
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?
My guitar chord generator.
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.
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.
Do not meddle in the affairs of sysadmins, for they are subtle, and quick to anger.
The old well worn bridge analogy: In theory it's pretty easy to built a bridge, but you need to only look at the Tacoma Narrows bridge to see that engineering a viable structure takes a bit more than str theory is prettSame deal with a space elevator. The theory is pretty straightforward, but the actual engineering to make a reliable structure is something else.
Engineering is the art of compromise.
What's lacking is the unobtainium.
Your post is a statement of religious belief. This WILL happen, and that WILL happen. Why? Because you say so?
The top of an intact space elevator in orbit would move eastwards, just like the ground under it does.
The top would move at a much greater speed than the ground, since it is further from the center of the earth and has to cover a greater distance for a full circle.
As any part of this elevator falls towards earth, it would keep its greater eastward speed and therefore overtake its anchor point quickly.
Less sense, actually. Trans-continental conveyors are at least technically possible. A space elevator violates basic physics, as people with more than two brain cells can easily see for themselves. One brief google brings up for example this post from 1995 which should give you all you need.
That's not an answer, that's another question, with plenty of unspecified assumptions which would let you come up with almost any answer you want. Lots of people have worked it out under various assumptions, and you get an answer requiring a cable with strength between 60-120 GPa. Scientists have measured carbon nanotube filaments which have a tensile strength in that range. We can't build an assembly (cable) that strong yet, but I wouldn't call that "violating laws of physics".Requiring research beyond our current knowledge and capability is not the same as "impossible". The most you can say is that it's not possible within the current limits of materials known to materials science. Why don't you link to a *proof* that no material can have a higher tensile strength than carbon nanotubes, and a *proof* that it not possible to bond carbon nanotubes so that an assembly has >50% of the strength of the filament.