Can we now build the "space tower"?

Very interesting article here reporting on researchers who had previously announced a rapid means of producing synthetic gem sized
diamonds, now believe their methods will work to produce diamonds of arbitrary size:
Artificial diamonds - now available in extra large. 18:11 13 November 2008 by Catherine Brahic. "A team in the US has brought the world one step closer to cheap, mass- produced, perfect diamonds. The improvement also means there is no theoretical limit on the size of diamonds that can be grown in the lab. "A team led by Russell Hemley, of the Carnegie Institute of Washington, makes diamonds by chemical vapour deposition (CVD), where carbon atoms in a gas are deposited on a surface to produce diamond crystals. "The CVD process produces rapid diamond growth, but impurities from the gas are absorbed and the diamonds take on a brownish tint. "These defects can be purged by a costly high-pressure, high- temperature treatment called annealing. However, only relatively small diamonds can be produced this way: the largest so far being a 34-carat yellow diamond about 1 centimetre wide. Microwaved gems "Now Hemley and his team have got around the size limit by using microwaves to "cook" their diamonds in a hydrogen plasma at 2200 °C but at low pressure. Diamond size is now limited only by the size of the microwave chamber used. "The most exciting aspect of this new annealing process is the unlimited size of the crystals that can be treated. The breakthrough will allow us to push to kilocarat diamonds of high optical quality," says Hemley's Carnegie Institute colleague Ho-kwang Mao." http://www.newscientist.com/article/dn16036
Original research article:
Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing. Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell J. Hemley Published online before print November 12, 2008, doi: 10.1073/pnas. 0808230105 PNAS November 18, 2008 vol. 105 no. 46 17620-17625 http://www.pnas.org/content/105/46/17620 [abstract]
The team's earlier research had showed they could make synthetic diamonds of perhaps 50% greater hardness than natural diamond. This should correspond to 50% greater compressive strength as well. Most discussion on the space elevator has centered on ultra strong materials for a cable in tension. However, according to this recent report, synthetic diamond production can now be scaled up to arbitrarily large sizes. So a compressive structure to space made of diamond might be feasible earlier, as diamond is much stronger in compression than in tension. I've seen various estimates for the compressive strength of natural diamond. If we take it as 400 GPa, then a space tower of diamond would have characteristic length of 400x10^9 Pa/(9.8m/s^2 x 3600 kg/m^3) = 1.13x10^7 meters, or 11,300 km. If this new synthetic diamond method really does create diamond of 50% higher compressive strength than natural diamond, then this length would be 17,000 km. And these are lengths without taper. Considering also that this maximal height for an untapered tower assumes constant gravity where in actuality the gravity is 1/16th as strong at 17,000 km altitude, it is possible that a tower made of diamond could reach all the way to geosynchronous altitude without taper. There aren't many references on the net available that do the calculations for a space tower in compression as opposed to a space elevator cable in tension. Here's one that gives the equations and some sample calculations:
Optimal Solid Space Tower. http://arxiv.org/abs/physics/0701093
Bob Clark
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Robert Clark wrote:

Hmm, I'm not sure that's the case. In fact, I'm fairly certain that's not the case. Hardness isn't linearly proportional to ultimate compressive strength, is it? Or to put it another way, if it is, why do we use two separate measurements?

There's a very good reason for this: buckling. You're proposing a very very tall, thin tower acting in compression, and assuming the failure mode is pure compression. It's not (not even close).
While we're at it, making the bottom so that it won't fail in compression isn't going to do you much good if the rocks under it will... In short, it's not the compressive strength of diamond you have to worry about here, as it's not what will limit it.
-- Brian Davis
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Dear Orval Fairbairn:
...

On the way up, the "lift cable" is pulled westwards, drawing the needed energy / momentum from both the Earth and the anchor. The anchor can have the rockets.
On the way down, the cable is pulled eastwards, of course.
David A. Smith
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N:dlzc D:aol T:com (dlzc) wrote:

And the rockets need fuel, which has to go up the space elevator, which will pull it to the west, which means the anchor will need to fire its rockets, which means they will need fuel... :-D
Pat
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Dear Pat Flannery:

Only initially. Once we have a presence in space, we can harvest much from the outer planets.

You can take *days* to restore the balance, or you can send a load of equal mass back down the tether. Then you get it all back.
The problem with the system is not how to operate it. It is in the materials available, and the planet being served has agents that destroy things for reasons other than Mankind's survival.
David A. Smith
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I suspect one of the things being misunderstood here is that the cable does not remain radial. As a mass moves along it, the cable is deflected east or west, which results in a component of the tension (a small component) to accelerate the mass west or east. What is changing the tangential velocity of the payload mass is the tangential component of the cable tension...

First, no: while the mass is ascending, it would indeed be "pulling back" on the upper portion of the tower, that's not a static situation, any more than a plucked string on a violin is. Second, with the ascending payload mass either removed or stopped, you have a situation where the cable as a whole has been deflected westward, yes... which means the earth tether point must be to the east of the cable, and therefore there's (again) a tangential component to the tether tension that is accelerating the cable as a whole eastward, speeding it back up.
I'm not sure why this is so surprising; I've given it to my P200 students as an exercise and had them get the right result (to be fair, I let them use a non-tapered cable, as that wasn't a problem I wanted to get them entangled in). Pearson put this all together very well in his paper (I think in the 70's?) on orbital elevators - perhaps you should acquaint yourself with the literature? It goes back further than that even. Here's a start:
http://www.star-tech-inc.com/id4.html
Note that the paper by Isaacs et. al., in 1966, is written by a bunch of folks who were oceanographers at the time. Seems only they had a lot of experience with very long cables hanging under their own weight (go figure :) ).
-- Brian Davis
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Dear Brian Davis:

Yes. Would look much like a pulled bowstring...
David A. Smith
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: You are *STILL* trying to get the boost/deboost energy for free. : Dark energy, anyone?
No, from the earth. Angular momentum anyone?
Consider in the abstract, a large mass spinning, a negligably small mass compared to the spinning mass, tethered to it, and a third movable mass attached to the tether. If the movable mass is moves outwards on tether, it's getting a velocity boost. Do you claim it can't possibly get this velocity boost from the tether, given that the tether is under tension?
Hint: if you push sideways on the tether, it will move it out of radial alignment, and it will slow or speed the spinning mass because the tension on the attachment point is no longer purely radial; moving a mass outwards on the cable speeds it up while slowing the spinning mass, and vice versa for inwards. Adding gravity to taste doesn't change this method; tethers can be used to get a delta-v out of momentum stored in a spinning mass whether the spinning mass is large enough to have significant gravity or not.
Therefore I expect it *can*, and the major remaining problem is damping the resulting oscillations.
Not that this means the remaining issues are trivial, or within near-future technological capabilities, but it works in the abstract, and no momentum is manufactured from thin ether, nor from dark anything.
Wayne Throop snipped-for-privacy@sheol.org http://sheol.org/throopw
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Dear Orval Fairbairn:
...

Incorrect. When the load goes up the tower / tether bends westward. The Earth drags / slignshots the payload, until about halfway up where the contribution from the Earth is about equal to the contribution from the anchor.

Your understanding is bullshit. Calm down and think about the physics.
Either direction the payload moves, the tension on the cable increases. But the tension tries to accelerate the tether satellite.
David A. Smith
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Dear Yousuf Khan:

Better read it again. Their method can produce gemstones of arbitrary size, and then yes they can "anneal" the color out of it.

That will be covered in their patent. ;>)

A little carbon added to iron does a lot, both good and bad. Perhaps dopants for structural use will have benefits (without causing too many side effects).
David A. Smith
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I'd hate to steel your idea...
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N:dlzc D:aol T:com (dlzc) wrote:

Well, I don't feel like reading it again. I'll just take your word for it. :-)

Perhaps carbon fibres or carbon nanotubes for tensile iron applications, and diamonds for compressive iron applications?
    Yousuf Khan
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:: Good grief. Isn't 490 GPa more than sufficient, or isn't it?
: Any strength whatsoever is sufficient for a space-tower or a : space-tether. It's just a question of tapering-ratio.
What's the taper for one constructed out of wet noodles?
"What I'm saying is, I could bench press the earth and I'd still have these little girl-noodle arms!"
--- Acacia Budur http://www.wapsisquare.com/d/20071107.html
Wayne Throop snipped-for-privacy@sheol.org http://sheol.org/throopw
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Wayne Throop skreiv:

Are they asian or italian noodles ?
Someone on rasfs did the math for a space-tether constructed from perfectly ordinary steel-cable a year ago or so. If my memory serves me correctly the thing ended up being several thousand miles across on the thick end for every square-mm of cross-section down here.
    Eivind
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