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Space Elevators Face Wobble Problem
Posted by
ScuttleMonkey
on Fri Mar 28, 2008 03:53 PM
from the all-part-of-the-ride dept.
from the all-part-of-the-ride dept.
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."
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A collision could cut the tether... (Score:5, Funny)
Re: (Score:3, Interesting)
This idea appears in Kim Stanley Robinson's Red Mars [amazon.com] when an elevator is cut and the asteroid at the far terminus of the space elevator is flung out towards the orbit of Jupiter.
Re:A collision could cut the tether... (Score:5, Interesting)
The design that specified steel cable did so specifically to show how impractical it would be to attempt a cable using existing materials.
Parent
Re: (Score:3, Interesting)
You:No, most designs specify a thin ribbon.
You're a politician, right?
Then why not a space escalator? (Score:5, Funny)
Re:Then why not a space escalator? (Score:5, Funny)
Parent
Re:Then why not a space escalator? (Score:4, Funny)
Well it makes perfect sense to me!
Parent
Re:Then why not a space escalator? (Score:5, Funny)
Parent
Re:Then why not a space escalator? (Score:5, Funny)
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Re:Then why not a space escalator? (Score:5, Interesting)
You do realize that most goods imported are imported on ships rather than airplanes, right? The reason for this is because while it is possible to import everything by airplane (as was done in the Berlin airlift) it is much more expensive to do so. In the case of a person traveling across the ocean the extra energy can be justified by the convenience of rapid travel. Most shipped items however don't have to be anywhere in any particular hurry so if it takes a few weeks for them on a boat it is no big deal.
Similarly a space elevator can be used for things such as hauling materials and supplies up to geosynchronous orbit and if it takes days or weeks or even months that's no big deal since the materials don't care. In the mean time the energy saved on transporting literally hundreds of millions of tons (eventually) of payload into space via elevator would be immense.
Parent
Re: (Score:3, Interesting)
One man's nonsense is another man's dream. Why dismiss something that's considered technically feasible? NASA scientists are taking it seriously [nasa.gov], too.
Once this structure has been built, and a few satellites loaded into orbit, it will begin to make sense even to the extreme skeptics. It would be nearly silent in operation, safer than riding a missile into orbit, and much cheaper once the initial construction cost is covered.
The materials are almost the
Re: (Score:3, Insightful)
Your post is a statement of religious belief. This WILL happen, and that WILL happen. Why? Because you say so?
Re: (Score:3, Insightful)
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 [google.com] 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
Re: (Score:3, Informative)
The experiment with the string requires you to keep the weight moving by pulling it with the string, a real satellite does not get pulled by a wire, it moves by its own inertia. The wire isn't what's keeping it in orbit, that's the combination of centrifugal force and gravity.
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Aircraft are struck by lightning as well, and survive too.
The entire craft (due to the benefits of being a Faraday Cage) rises up to high voltage almost all at once,
meaning there is no serious voltage difference across the craft, therefore no dangerous currents, therefore no power dissipated into the craft.
A tether holding a satellite in place and attached to the Ground (KEY WORD) will have All of the voltage of a lightning strike across it, so the hundreds of tho
Re:Then why not a space escalator? (Score:4, Interesting)
Their copper tether was nowhere near as long as a satellite tether would be, and theirs wasn't shorting out a thunderhead like a satellite tether would,
Now, IF you could somehow manage the danger of a sudden lightning strike, I think you're right that there would be large voltages across the length of the tether, and you should be able to harvest it for a power source. The act of harvesting the electrical charges might even be a part of the solution..
Parent
Just let it wobble! (Score:2)
This is awesome (Score:2, Funny)
Re: (Score:3, Funny)
"It's not the jumping part that hurts...it's the sudden stop at the end."
In good company (Score:3, Interesting)
being unstable doesn't preclude it being usable (Score:5, Interesting)
For instance most modern fighter aircraft are aerodynamically unstable, but they still fly. For example, the F16 was deliberatly designed to be unstable (to gain better manuverability). Of course the F16 has a computer control system to make it flyable by humans, but if the computer dies, well, unstable tumble modes ahead... I've also antecdodally heard that some modern bridges and tall-buildings are also not inherently stable (and are actively stabilized by computer control systems).
But to be honest, I think the engineering of a space elevator is pretty much beyond our forseeable technical ability (material science, control systems, assembly techniques, not to mention project management, risk/return estimation, and financing/underwriting).
If you think the problems are merely about waiting for technology, just think of the chunnel. It was imagined for a long time, but even after they got all the science and technology and assembly issues under control, the project management, risk/return estimation and financing/underwriting issues managed to kill a few companies before if finally got done.
Parent
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Specifically if you have a tether you can feed a charge onto it and it will either get pulled in or pushed out by the earths magnetic field.
This may be useful for stabilizing portions of the tether and controlling any vibrations that develop.
When will it become a reality? (Score:5, Interesting)
"Clarke answered, 'Probably about 50 years after everybody quits laughing,'" related Pearson. "He's got a point. Once you stop dismissing something as unattainable, then you start working on its development. This is exciting!"
http://science.nasa.gov/headlines/y2000/ast07sep_1.htm [nasa.gov]
It's easier to postulate than actually engineer (Score:4, Insightful)
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.
Parent
Of course it's going to wobble! (Score:3, Interesting)
any who has ever seen cartoons as a kid would know this :p
I am more concerned about the static problem (Score:4, Interesting)
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Re:I am more concerned about the static problem (Score:5, Informative)
They do both. As the storm builds up the lightning rods help to diffuse the charge. This is one reason why they have sharp ends; electrons leave a charged conductor more readily at points of higher curvature. The pathway thus created then becomes the preferred (low-resistance) route to ground in the event of an actual lightning strike.
Parent
Of course it's not easy (Score:5, Insightful)
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 (Score:5, Insightful)
Parent
"I think" Engineering (Score:5, Insightful)
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 (Score:5, Insightful)
Re:wreck the elevator (Score:5, Interesting)
Parent
Re:wreck the elevator (Score:5, Insightful)
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?
Parent
no, it would go east. (Score:4, Insightful)
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.
Parent
Insightful? (Score:3, Informative)
Re: (Score:3, Funny)
And you thought it was bad (Score:4, Funny)
Kids pressing all the buttons... (Score:5, Funny)
launch loops (Score:5, Informative)
Unlike space eleveators, launch loops require no exotic materials (just iron and steel), are essentially self-erecting, are anchored, and accelerate people quickly through the radiation belt.
We could probably build a launch loop in a decade or two, if we embarked on an Apollo-like program.
The Stealth Fighter and Bomber Are Unstable, Too (Score:4, Interesting)
The Stealth Nighthawk fighter could not be controlled by a human, it is so aerodynamically unstable. But with the help of some good software, that plane flies. The same is true of the B-2 Batwing bomber, it only flies because a computer stabilizes it.
There will be controllable vanes (for the atmosphere) and thrusters (for space) to control the car's behavior. The wobble would be predictable and all the traffic would be required to avoid it, in the same way power boats are required to steer around sailboat.
The bigger problem with space elevators... (Score:5, Funny)
So then? (Score:3, Funny)
They've solved the elevator music problem?
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Re: (Score:3, Interesting)
#1> You don't have to go all the way to orbit.
There are several ways to split this up. Skyhooks [wikipedia.org], Partial elevators etc. The cool part about these are that they aren't nearly as vulnerable to terrorists due to their high altitude.
#2> The space elevator can be active. See Space Fountain [wikipedia.org]