The space elevator: going down?
Study shows that proposed carbon nanotube cables won't hold up.
Is it possible to make a cable for a space elevator out of carbon nanotubes? Not anytime soon, if ever, says Nicola Pugno of the Polytechnic of Turin, Italy. Pugno's calculations show that inevitable defects in the nanotubes mean that such a cable simply wouldn't be strong enough.
Read the story here.
Comments
A carbon nanotube cable would be an electrical conductor. It would short ground to atmosphere to ionosphere. It would cut through the Earth's magnetic lines of force as the magnetosphere billowed, as during solar storms. It would generate planet-scale electric pontentials and currents.
Fireworks. Very expensive use-once-and-toss fireworks.
Posted by: Uncle Al | May 22, 2006 03:26 PM
Al, nice to see you post in places that aren't usenet.
This paper could be important. More study is (it always is) indictated before we simply toss up our hands and call the space elevator a done deal.
Posted by: Brian | May 22, 2006 05:45 PM
Although not a new suggestion, such space elevator looks quite strange.
My first concern is about how would the geostationnary satellite remain on its orbit ? Indeed, each piece of cable underneath should rotate more an more rapidly to remain in dynamic equilibrium. In brief, the satellite would feel a huge additional weight not balanced by centrifugal force and, inevitably, would fall down on earth.
Let's suppose I am wrong and this is possible. Then comes my second concern: how to prevent the huge resonant oscillations that would appear in this cosmic 'guitar string' ?
Kepler, who thought of the "music of spheres", would certainly have loved the idea but, not less certainly, dismissed the project.
Philippe Dumas
Posted by: Philippe Dumas | May 22, 2006 06:20 PM
Been compiling the elevator statistics for a year now and this just adds more damaging evidence to it. Nothing is impossible - including the Law of Thermodynamics going backwards- but the number of things going against the space elevator gives a probability of success lower then that.
You need to protect it from many different environments it passes through and that adds weight. If you do the calculations, you do not get much “throughput” and selling the “ticket” at a low cost per pound (that is why we are doing it, right?), makes the payback thousands of years, if at all.
Posted by: Module | May 22, 2006 06:34 PM
I've read about this elevator thing for quite a while but I still miss the point why this should be so much more efficient in getting things to orbit.
Just liftig won't do, I always thought things have to be accelerated too to stay in space. And how does it compete with rockets' simple braking by friction with air to get down again?
The elevator has to put all the orbital energy back into the cable while objects descend or the cable has to transfer it to a simultaneously lifted object.
Wouldn't that add much more force to the cable than the weight itself unless one will wait for months until something is lifted or brought back?
Posted by: Clint | May 22, 2006 09:41 PM
As a professional designer of advanced space systems, I'm skeptical of the near-term feasibility of an Edwards-style space elevator. But this article is a bit overly negative; 62 GPa is not a magic number. A tensile strength of 30 GPa, or even 15 GPa, in macroscopic cables is enough to make an elevator with a tapered cable feasible from a simple strength-of-materials standpoint.
Posted by: Jordin Kare | May 23, 2006 02:51 AM
I've followed the SE concept for awhile, and one thing that's often overlooked in the "are nanotubes strong enough" question is our ability to stitch or braid them together like we do for rope and steel cables.
While it's true that a single 100,000Km nanotube is likely to fail under 62GPa (or less) stress, a well engineered nanotube ribbon, rope, or other structure is much more likely to succeed under much harsher conditions.
I believe it's been said that we could build a space elevator out of bubble-gum if we wanted -- but its base would be half the circumference of the Earth.
Posted by: Singularity | May 23, 2006 03:22 AM
There is an alternative approach to a space elevator which does not need a long, continuous cable run.
See details at:
"A New More Practical
Approach to a Space
Elevator", at
www.aoi.com.au/pandora/frames7566.htm
Posted by: David Noel | May 23, 2006 07:11 AM
You seem to editorialize the usefullness of space elevators. It seems mathmatically possible to build a space elevator on the moon (signifigantly less gravity and very little atmosphere) with a strange and exotic substance known as "steel". Such a device would be an incredible boon in any intergalactic economy. Space elevators are possible and will come about, sooner or later, either on earth or not.
Posted by: Trey Cundall | May 23, 2006 09:18 AM
Space elevators are like an enormously long train track that supports a dozen tiny rail cars along its entire length, with scheduled service only once a week. Even if some magic unobtainium zero-cost material could build a no-taper Edwards cable, and launching that material was free, the logistics of the space elevator make it close to useless.
Consider dynamic structures, such as the launch loop (www.launchloop.com), or various forms of orbital ring or spaceport. While those have their own issues, the launch rates scale in an unbounded way, and energy handling is much easier. A true space transportation system will move dozens of payloads per month, not per week, and hopefully can be deployed by the dozens rather than one per planet.
I just set up a wiki - a community editable bulletin board - at wiki.launchloop.com . If you want to discuss space elevators, or dynamic structures, or anything else space related, we can continue the discussion there.
Posted by: Keith Lofstrom | May 23, 2006 04:02 PM
Space Elevator Carbon Nanotube Shapes.
Having worked with cranes and wire rope of steel that is a machine unto itself I suspect that round is better than flat or square and that hence the conveyance shape of flawed nanotube inherant construction ought to be round, though possibly hollow to overcome the flaws of materials, which all respectful engineers take into account in order to accomplish the goal.
We are here to figure out how to do what needs to be done.
We are not here to figure out how not to do what is to be done.
transcendia.org
Posted by: Russell Scott Day | May 24, 2006 01:58 AM
Wow, there's a lot of nonsense in this thread. Where to begin?
First, no, you can't build a space elevator on the Moon, because there are no selenosynchronous orbits in the standard sense -- though you could perhaps try for one of the Lagrange points.
Second, the reason the top of a space elevator doesn't fall down is that it's in orbit. The center of gravity of the entire system -- including both the "downward" cable and the counterweight -- is in geosynchronous orbit.
You don't have to accelerate things, in addition to lifting them to GEO altitude, is because they're already moving at the right RPMs for that orbit. That's what GEO (geosynchronous) means.
Of course you are increasing the payload's linear velocity, and that energy comes from the elevator. But the elevator's mass is so much greater than the payload that it doesn't affect it much, and anyway, it gets that energy back when payloads go back down the elevator.
Dynamic oscillations and electrical conduction are minor issues, and ones the engineers have already considered.
But kudos to Jordin for pointing out that there is no magic strength threshold -- a weaker material simply means you need more taper. At some point, of course, it becomes impractical, but that point isn't necessarily 62 GPa.
Posted by: Joe Strout | May 24, 2006 04:00 AM
"Researchers think that the best shape for a space-elevator cable would be a ribbon, about a metre wide and as thin as paper. It would need to withstand at least 62 gigapascals (GPa) of tension. That's about as much as in the rope of a tug-of-war with more than 100,000 people on each side."
Bit of a shame to see a tension (a force) stated in units of GPa, in a scientific magazine.
Posted by: Greg Locock | May 24, 2006 07:46 AM
"The idea of a space elevator was popularized in science fiction..."
Best place to start is "The Fountains of Paradise", by Arthur C. Clarke.
Posted by: Jon Herbert | May 24, 2006 05:05 PM
A space pier (100km tower with an accelerator at the top) would have cost benefits nearly as good as a space elevator but without pushing materials to the limit.
http://discuss.foresight.org/~josh/tower/tower.html
http://discuss.foresight.org/~josh/tower/economics.html
A space pier only needs 5 gigapascal strength material. Various PAN fibers are that strong as is M5 Fiber, which exist are being made in factories now.
http://www.m5fiber.com/magellan/m5_fiber.htm
30Gpa carbon nanotubes would still make fantastic skyhooks, which could be rendevoused by relatively inexpensive sub-orbital space planes.
the space elevator people can also make money with better High Altitude Long Endurance platforms as the materials and climbers improve.
http://www.spaceref.com/news/viewpr.html?pid=18999
Posted by: Brian Wang | May 25, 2006 06:54 AM
Not anytime soon, if ever, says Nicola Pugno...
Never is a long time.
Posted by: Computer Games Lover | May 27, 2006 01:14 AM
1. Science fiction didn't postulate the concept of a space elevator, Russian scientist Yuri Kondratyuk did in the 1920s
2. Arthur C. Clarke, expanding on the work of Kondratyuk and other scientists, used the concept in his book "Fountains of Paradise" and postulated the use of a diamond-based filament material for use in the anchoring system
3. Pugno comes out of left field denouncing a technology that has not emerged from its infancy (carbon nanotubes), and claims that they will never be strong enough?!?!
Yeah, using today's technology to make them he is probably correct, but technology never stands still and no one said that the anchor system HAD to be made of carbon nanotubes. It has to be made from a material that can withstand ALL of the stresses it will encounter in operation. Today, carbon nanotubes show the greatest promise, but they certainly aren't the end-all, be-all solution for the success of a space elevator. I can't believe Nature would publish this. Pugno is clearly just after publicity and trying to attack something that he just doesn't agree with. If he's going to shoot down carbon nanotubes, the least he could do is postulate a better solution. And how can he definitely say that it won't happen in his lifetime?!?! That's pretty naive and right up there with people saying that Mac OS X based computers couldn't be used for a supercomputing cluster, before 2003 when I helped build one!
To the other posters, there are plenty of books and papers to answer some of the more simple (and complex) questions you have asked. Most of them are available through public, or university libraries. A simple Google or Amazon search will give you titles and ISBN numbers. And, even though Arthur C. Clarke's book is a work of fiction, it still contains a lot of real science in it.
Posted by: Jason Lockhart | May 27, 2006 03:23 AM
If you are interested in SE, check out the Liftport forum at http://www.liftport.com/forums/. Many of the points raised here have been addressed there.
Some points:
Practical issues about something this big sticking through the atmosphere are still unknown, and will be until an SE is in place. Both the models that predict success and those that predict failure are based on inadequate data.
The current thought is that the SE does not stop at geosynchronous orbit, but rather stretches out to about 62,000 miles. The mass of the structure on the other side of geosynch serves to lift the structure, and thus removes the need for a big mass to anchor it at geosynch.
No one currently is envisioning a single nanotube the entire length of the ribbon. The nanotubes will probably be much shorter. They will be set in a high shear strength matrix, so the strain will be spread across a number of tubes.
It should be possible to build a SE on the Moon, provided it passes through L1.
Arthur C. Clarke said something to the effect, “When an eminent scientist says that something is possible, he is almost certainly right. When he says something is impossible, he is quite possibly wrong.”
Posted by: Mike Brennan | May 27, 2006 03:41 AM
The material strength requirements could be significantly reduced by attaching helium balloons to the tether at various points. Baloons have been flown up to 33km high, see http://www.esa.int/esaMI/Cassini-Huygens/SEMWNPYO4HD_1.html. Wind then becomes an issue. It might me necessary to triangulate - have tethers from three separate points join at about 30km above the earth's surface, and have a single one from there on up. Of course three tethers weigh more than one, but their weight would be carried by the helium balloons.
Posted by: Trevor Turton | May 27, 2006 02:27 PM
I would think electromagnetic launch sleds would work to put objects into moon orbit just fine and inexpensively. But a cable such as this one might be useful on Mars, for example. And surely the engineering constraints would be milder given that planet's lesser surface gravity.
Obviously a "beanstalk" isn't going to happen tomorrow. Long term (100 years?) it appers feasible for consideration. Unless some cheaper/simpler method hasn't taken over by then.
Progress on the latter over the last 40 years doesn't appear too promising, but maybe advances in, for just a few examples, titanium smelting, emag launch boosters (such as Inductrack technology), and various ramjet technologies might seriously reduce launch costs in a few years.
Not predicting, mind you, but a variety of technologies, some not even particularly cutting edge, lend hope of radically reducing launch costs to levels that are merely high rather than "astronomical."
Posted by: Hal Porter | May 30, 2006 02:57 PM
I'm bothered by that comparison of 1 missing atom per 10^12 atoms, based on one defect per 4um.
Assume maybe 7 atoms per nanometer (probably a bit less), and 4um is 4000x that - or about 28000 atoms = 2.8e4 atoms.
One defect in 4um would mean the circumference of the nanotube would have to be about 36 million atoms to have 1 missing carbon in 1e12! What am I missing here?
The site of the defect is much more reactive. That seems to imply that it might be possible to cause a reaction at that point that patches the 'hole' - perhaps perfectly, perhaps with a weaker bond - but in either case the net reduction in strength should be far less.
And suppose the nanotubes were woven into a mesh, with grid size about 0.1um. For every defect, there'd be 38 mesh cells intact. So long as the strength of the other cells can be transferred to the mesh above (rather than only to the damaged tube), the weakening would be about 1/40th or at worst 1/20th of the effect for a single nanotube.
So I'm questioning what kind of mathematical model Pugno was using...
Posted by: TomC | June 15, 2006 10:24 PM
Rob Carlson has posted on the Launchport book here
Posted by: Oliver Morton | June 16, 2006 10:24 AM
Study shows that proposed carbon nanotube cables won't hold up.
I do not agree.For more info go to System.String[]
Posted by: warsaw hotels | September 25, 2006 09:34 AM
At this time orbital tethers are the only space elevator concept that is the subject of active research and commercial interest in space. However, there are two related concepts worth mentioning: a space fountain and a very tall compressive structure (i.e. a structure that stands on its own).
A space fountain would use pellets fired up from the ground by a mass driver, the pellets traveling through the center of a tower. These pellets would impart their kinetic energy to the tower structure via electromagnetic drag as they traveled up and again as their direction was reversed by a magnetic field at the top. Thus the structure would not be supported by the compressive strength of its materials, and could be hundreds of kilometers high. Unlike tethered space elevators (which have to be placed near the equator), a space fountain could be located at any latitude. Space fountains would require a continuous supply of power to remain aloft.
Posted by: Thomas | December 12, 2006 01:24 PM
There are five geostationary or trojan points on the earth. Only one is over land. This is the most stable of the five. At Sri Lanka. Is it any wonder that Arthur C Clarke chose to settle at Sri Lanka.
Posted by: Cyberbian Peripetetic | August 22, 2007 08:15 AM
The ribbon alone as pointed out albeit derisively, could provide a conduit from space to earth to bring electricity safely from solar arrays. That would provide unlimited power to earth.
Microwave transmitters would only be used to cook us all in the end.
Posted by: Cyberbian Peripetetic | August 22, 2007 08:22 AM