Talk:Space elevator

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[edit] Article organization still has a big structural problem

I wandered away from this article for a while to do other things but I think a major problem I raised in #About this word 'Plausible' is still unresolved. The intro paragraphs for this article talk about how all sorts of structures that reach from ground to space fall under the classification "space elevator", and then there's an "orbital tether" header and everything after that reads like a separate article on just orbital tethers. Basically, there are two separate articles on two different topics that are spliced together in one page. My proposal before was to split off the orbital tether section into its own article (orbital tether), leaving space elevator as a general overview of the various concepts, and although objections was raised they were very nonspecific as to what was wrong with the idea. Does anyone have any other solutions to suggest, or specific details as to why my proposed solution is bad? Bryan 20:13, 14 January 2006 (UTC)

I more or less did this once already, and people reverted it. I didn't call it orbital tether I called it 'beanstalk'; but otherwise that's what I did. I think there's enough people that think that space elevator == beanstalk/orbital tether that it won't fly.

Besides who says that space elevator really isn't just a beanstalk? Is a space fountain actually a space elevator? Is a space elevator a structure that reaches space or is it just another name for a beanstalk? Near as I can tell wikipedia has a significant chance to define what 'space elevator' exactly means here. It's not totally clear.WolfKeeper 21:03, 14 January 2006 (UTC)

Well, we shouldn't decide what these things should be called - that'd be original research. All I'm proposing here is that this article should be split because it's two articles smooshed together, what we ultimately call these things is ambiguous and we'll need all sorts of "also known as"es in the opening line. Bryan 22:37, 14 January 2006 (UTC)
Shouldn't the history part head the article ? --Anne97432 06:59, 27 April 2007 (UTC)
The terms "bean stalk" and "space elevator"[1][2] are generally used interchangeably in the engineering literature to refer to an anchored cable or tower extending from Earth/ground to Geosynchronous Earth Orbit and a bit beyond with the counterweight. "Fountain" is a special elevator, the structure rides a high speed momentum exchange medium (typically iron/steel loops) rather than supporting itself. An orbital/space tether[3] (also a standard term easily citable in the engineering literature) is a completely different animal from an engineering and operations standpoint. Merging/leaving these two in the same article makes about as much sense as putting sea ferries in with bridges. The key difference is that one rides/climbs the elevator/beanstalk/tower like an elevator. The space tether (skyhook) tosses the cargo on vector planned. In my opinion Wikipedia would be better off with a couple of appropriate stubs or half articles ... assuming they could avoid deletion while they were improved. Anybody interested could start a discussion of engineering details or approaches at www.wikiversity.org Perhaps a decent summary of various engineering approaches would eventually result that could be transwikiied/merge back to Wikipedia. Lazyquasar 02:01, 25 September 2007 (UTC)

[edit] Why use power to lift?

Cut the teather... Let the lift fall to space. No energy needed for it to reach space other than the couterweight! Construct a Lift Station in space that controlls the teather so the shipment and the couterweight do not fall into space.

                                   O --- Lifting Couterweight
                                   |
                                   | --- Lifting Cable
                                   |
                             -------------
                             |           |  ------ Lifting Station 
                             -------------
                              |    |    |
                              |    |    |   ------ Station Teathers
                              |    |    |
                              |    |    |
                              | (=====) |   ------ Cargo
                              |         |
                              |         |
                    --------------------------------

Lifting Station controlls rate of Lifting Cable passed through it. Multiple teathers attach Lifting Station to the ground, station is and acts like its own couterweight. Guides can be attached to station teathers to controll cargo as it heads toward space. In the event of the lifting cable breaking the cargo would not fall to space or earth by safety devices that can be placed in these guides. Station would also be able to assist in getting the cargo going in the direction it needs to be going after it reaches space. —The preceding unsigned comment was added by 71.8.208.173 (talk • contribs) 19:46 UTC, 5 June 2006.

That's an interesting idea, but here isn't the place to discuss it. This talk page is for helping to put together the encyclopedia article, not for general chat about space elevators. If you can provide a reference for that plan, then let us know and we'll add it to the article. If it's more your idea and you don't understand why it isn't done that way then you could ask the reference desk, or if it's your idea and you want to publish your ideas, then you need a web host or a scientific magazine, depending on your level of expertise. --HughCharlesParker (talk - contribs) 19:15, 5 June 2006 (UTC)
Maybe there should be an article for this kind of idea(s)? I mean... wikipedia is a tool for the amassing and pursuit of knowledge, no? "Space Travel Theories" or something. Degen
dont worry about it Degen theres alot of unimaginative white coats on here who's only pleasure is lots of numbers. —The preceding unsigned comment was added by 82.36.32.73 (talk • contribs) 00:55, 4 October 2006.
It's not that I'm only interested in numbers. I'm here to further the wikipedia project, as we all are, and wikipedia is about building an encyclopedia. Two useful pages to read if you want to gain some insight into how the project works are our policy page and our page about what wikipedia isn't. Particularly, wikipedia isn't for original research - material we use must be verifiable by citing a source. --HughCharlesParker (talk - contribs) 09:18, 16 May 2007 (UTC)
Discussion of engineering details or concepts are welcome at http://en.wikiversity.org/wiki/School:Engineering Any applicable information or summaries are easily ported back to Wikipedia as both currently use the GFDL. Lazyquasar 02:06, 25 September 2007 (UTC)

[edit] Carbon nanotubes

I was at a talk about carbon nanotubes a while ago and the speaker mentioned that they would be a likely material to be used if a space elevator was ever built. This is already mentioned in the article. Can anyone back this up with a published source? savidan(talk) (e@) 17:09, 14 June 2006 (UTC)

Well, who was the speaker at your talk, and was the lecture recorded? We could use that. siafu 19:14, 14 June 2006 (UTC)
No, they would not be a likely material. It just makes no sense at all, somebody just like s the sound of "carbon nanotubes". UHM (Ultra-High-Modulus) Carbon Fiber is at least two orders of magnitude more reasonable as a material for the cable, since it's component monocrystalline domains are two orders of magnitude longer. It's still ridiculous, but at least it pretends to make sense, where as the "carbon nanotube" idea only *sounds* good. I tested short lengths (~ 1 cm) of carbon fiber with a modulus of 130Mpsi to failure at nearly 1% strain, or 1.2 million psi. Still you couldn't make a space elevator cable out of it...
—Preceding unsigned comment added by 131.215.115.31 (talk) 15:13, 10 July 2007

[edit] Center of Mass?

I believe the diagram is incorrect. It labels the point on the cable which intersects the imaginary line of "geosynchronous orbit" as "center of mass". But wouldn't the center of mass, by necessity, be at an altitude higher than geosynchronous orbit? I would think that no matter how heavy the counterweight is, if the center of mass of the entire system (cable + counterweight + any climbers) falls below the height of geosynchronous orbit, then the entire thing would collapse. Ravenswood 17:12, 21 July 2006 (UTC)

I don't think it would collapse. By conservation of angular momentum, if the COM fell below GEO, it would increase in angular velocity relative to the Earth, which would greatly incrase the tension on the cable and potentially sever it. siafu 17:27, 21 July 2006 (UTC)
Assuming it didn't snap, it would increase the angular velocity for a while- the cable would swing eastwards until the tether point slowed and then stopped it. At that point the cable would begin to fall more. It would then swing backwards the other way, and then fall more, eventually it would end up at ground level or burn up in the atmosphere, or a mixture..WolfKeeper 05:22, 2 September 2006 (UTC)
Odd orbital mechanics... The centre of mass will be sufficiently above the geostationary orbit to provide the tension in the cable. If the tension is small, and the mass is large (both reasonable assumptions) then the equipment needed to measure the difference in altitude may be more like a microscope than a ruler.
The question was what would happen if the centre of mass did go below Geo though. I still think if it was modestly below, it would rock back and forth a few times. However as it starts to fall, coriolis force kicks in and pushes it to the East, and it ends up wrapping itself around the Earth/burning up.WolfKeeper 16:43, 2 September 2006 (UTC)
In considering the mechanics, I think one has to avoid saying "If it falls below..." becuase there will be a reason why it is depressed - an applied force. WHen the centre of mass descends, it speeds up, potential energy being converted to kinetic. It won't swing back and forth and drop on teh floor. Midgley 16:07, 2 September 2006 (UTC)
The thing is that the length of the cable is roughly constant, so if it rocked back and forwards the altitude varies depending on the angle from the vertical. If it was to move far enough (and there are a number of drivers, such as tidal forces, and coriolis force due to climbers) it could in principle fall over.WolfKeeper 16:43, 2 September 2006 (UTC)

The diagram is incorrect, and most of the language involving the center of mass is as well. The center of mass is nowhere near GEO. It is not expected to, because different parts of the structure experience widely different gravitational and centrifugal acceleration (in the rotating frame). The gravitational acceleration near the surface is much greater than the centrifugal acceleration beyond GEO, meaning the part of the elevator beyond GEO altitude is much more massive than the part below. If you don't believe me, take a close look at the Cable Taper Plot. What needs to balance on both sides of GEO altitude are the forces, not the mass, and less acceleration means more mass. It does not matter, though, because center of mass is not a useful concept for extended objects in an inhomogeneous field anyway. To say "the center of mass is in geostationary orbit" is plain wrong. If I get some consensus, I will edit the text, but I do not know how to edit the diagram. Andreas 20:00, 13 June 2007 (UTC)

[edit] Pretzel logic

The article currently contains the following paragraph:

A possible complication not mentioned in most of the literature is the potential 'pretzel-effect' of a carbon nanotube ribbon which would, without wind mitigation, ultimately twist into a pretzel shape in the areas of the ribbon exposed to the atmosphere. The added tensile stress from these forces could break the ribbon and it admits of no simple solution. If the constant minimum load tension in the ribbon is sufficient (some have suggested 20 tons) such twisting may be mitigated by this tension alone. A cylindrical, cable shape eliminates this concern entirely as the twisting need only be mitigated at the end points.

I had to read this three times before I understood what it was trying to say, and that only because the vision of a paper streamer in the wind suddenly popped in my mind. This is screaming for a visual illustration... linas 04:49, 11 December 2006 (UTC)

Linas, if you understand what this is trying to say, you're doing better than I am. To my thinking, a "pretzel shape" is an overhand knot, and there's no way that wind could "twist" a ribbon cable into that shape. I think this passage needs rewriting. KarlBunker 11:55, 14 December 2006 (UTC)
[Later] Okay, I guess I should have looked at the article for pretzel, or perhaps an actual pretzel. A pretzel twist isn't an overhand knot and doesn't require that one end be free, so it could happen to a wind-blown cable. Still, this could use some better description; maybe "twisted into a pretzel-like loop"? KarlBunker 14:44, 14 December 2006 (UTC)
This paragraph makes no sense whatsoever. It has no sources, and should be deleted.
In fact, I think I will go ahead and do so. Andreas 02:58, 13 June 2007 (UTC)
Good move, especially since "wind mitigation" is discussed in almost source. siafu 03:13, 13 June 2007 (UTC)

[edit] Insignificant Slowing of the Earth

How can the slowing of the earth caused by the existence of the lift only 'insignigicantly slow' the Earth's rotation? Surely any slowing of it's rotation is a very bad thing and would need some form of countermeasure? The fact that this topic was skimmed over in the wiki gave me cause for concern. 129.11.76.215 09:04, 1 March 2007 (UTC)MrLaister

The same way that whenever you walk towards the west the earth is insignificantly slowed (and insignificantly sped up when you walk to the east). The great disparity of mass of the earth versus your body (or indeed a space elevator and payload) means that the actual slowing experienced is so infinitesimal as to not warrant worry, but does deserve a breif entry into the physics section of the Space Elevator wiki. Also, presumably an operational space elevator would have mass coming down as well as going up, so there's your countermeasure. ABVS 01:58, 3 March 2007 (UTC)
Or it may be the other way around - east slows, west speeds up... sun rises in east.. earth rotates to east... yes I think I was wrong the first time.ABVS 01:10, 4 March 2007 (UTC)
The angular momentum of the Earth is: 7.06 x 10^33kg m^2/s[4][5]. The angular momentum of an object weighing 1000 kg (1 tonne) in Geosynchronous orbit is 42,164,000m[6] * 3071 m/s * 1000 = 1.296^14 km m^2/s. So to add 1 second to a year we would have to decrease the angular momentum of the Earth by a fraction of 1/(365.25*24*3600) = 1/31557600. Multiply that by the angular momentum of the Earth and divide by the angular momentum of the object and we get 1.726 e 12. In other words you would have to launch a million, million tonnes into Geosynchronous orbit to slow the rotation rate by 1 second per year (if I haven't messed up my arithmetic.) But even if we did that, the normal variation of the rotation of the earth is about 1 second a year anyway (see leap second), due to weather and other effects, so nothing bad would happen(!) Hope this helps.WolfKeeper 03:23, 3 March 2007 (UTC)

[edit] Any English info on the hanging tether idea?

Like the title says, I'm wondering if there is any information on the hanging tether idea. It's basically the same idea as the normal elevator, but is only 4K long (with COM at 2km), and the Earth end of the cable has a sky-hook/platform for rockets to transfer cargo to the elevator. I understand that it's being developed for the next X-prize, but I only have Japanese language sources on it so I don't want to add it to the article. Anyone know anything about it? -- Bakarocket 17:01, 6 March 2007 (UTC)

The idea was discussed extensively by Robert Zubrin in an article in Islands in the Sky: Bold New Ideas for Colonizing Space (ISBN 0-471-13561-5). I don't know anything about it being part of the next X-prize, though. siafu 17:57, 6 March 2007 (UTC)
Should it be added into the article as an alternate version in 4.3, or is there another article already available? For the X-Prize part, I just did an interview on a guy involved with the project, which is why I came here looking for some back-up. It would be intellectually dishonest for me to use my own print article as a source though, which is why I was looking for other English sources. I've never touched this article, so I thought I'd ask the regulars first. -- Bakarocket 18:30, 6 March 2007 (UTC)
Where is your article published? siafu 16:43, 10 March 2007 (UTC)
It won't be out until next month, and it'll be in an English newspaper in Japan. I'm not going to add anything until I can source it from Zubrin's piece, though. I'd feel dirty.-- Bakarocket 05:04, 11 March 2007 (UTC)

[edit] similar applications?

I'm intrigued by the idea of a space elevator. But surely there are similar applications that would cost far less to implement and should be mentioned in this article. Off the cusp, I can imagine a space pump for ridding the world of gaseous, solid, and nuclear waste. We could pipe all our waste to a network of regional pipes that could then be ejected through a central space pump into outer space. Obviously, the harmful waste would have to be ejected with a sun-bound trajectory so it would be incinerated. Bet that would put a significant dent in our polution and waste problems. Moto 02:31, 10 March 2007 (UTC)—The preceding unsigned comment was added by Teeroy (talk • contribs) 02:21, 10 March 2007 (UTC).

SOrry, what? Are you suggesting a new form of transport?--Bakarocket 12:00, 10 March 2007 (UTC)
How is that different to a space elevator? Wouldn't that in fact be orders of magnitude more difficult, what with having to build a pipe instead of a cable, not to mention designing a pump that could handle a head of several thousand kilometres...ABVS 00:10, 11 March 2007 (UTC)
It's different in that Space Elevators are being researched and Space Garbage Disposals aren't. --Bakarocket 05:04, 11 March 2007 (UTC)

[edit] Poisson ratio and elongation?

Partly as a matter of interest and partly because maybe it should be added to the page, does anybody know how elongation and deformation from tension (and maybe even tidal forces) would affect the calculations? —The preceding unsigned comment was added by 207.112.60.14 (talk) 00:01, 29 March 2007 (UTC).

Given that the loading is purely axial, the poisson ratio is not so important as the cable taper can easily be designed to account for the stretching effects. According to our article on carbon nanotubes, the elastic modulus of the material is on the order of 1 TPa; just back-of-the-envelope assuming a length of 42,164 km (GEO), an average thickness of two meters (a convenient cross-sectional area of pi meters), and a loading at the "end" of ~70 MN (this one is just a guess), the total elongation would be about 940 m. This is about 0.0022% the entire length of the cable (i.e. the strain is 22E-6). This would affect the caculations only very slightly, but would be more important in calculating the oscillating behavior of the structure, which is much, much, more complicated. siafu 01:00, 29 March 2007 (UTC)

Ok, I looked into a little more. If you look at the Pearson article (reference number 7 i tihnk), on pg. 10 he has a discussion on elongation. When the tower stretches, more of it is passes geosynchronous orbit which, in turn, stretches it more. For a tensile strength/Young's modulus of .0482 he gives a stretch of 5%. Nanotubes have ~.06 which would give an even higher stretch. Unfortunatly I didn't see this mentioned in any of the other article so I'm not sure what the deal is. 207.112.60.14 04:08, 29 March 2007 (UTC)Yonni

You are right. The Young's modulus (1TPa) and required tension (50-60 GPa) fix the elongation at 5%-6%. The 0.0022% number above must be a mistake. Andreas 14:20, 13 June 2007 (UTC)
The calculation is right enough; it was a guess based on faulty data. siafu 14:26, 13 June 2007 (UTC)

[edit] Wouldn't The Counterweight change the earth's orbit and kill everyone

Anyone? —The preceding unsigned comment was added by 24.168.30.85 (talk) 01:25, 29 March 2007 (UTC).

No. siafu 01:45, 29 March 2007 (UTC)

[edit] Citation needed

I've removed these from the article - hopefully someone out there is involved in maintaining the article who can deal with them. I hate to see these tags on a featured article, and the onus is really on whoever added them to provide a reference. Richard001 08:51, 5 April 2007 (UTC)

  • One rather recent discovery is that high wind speeds can flatten the elevator cable horizontally across the surface of the Earth perhaps a hundred kilometers. Surprisingly, the stress on the cable is not significantly increased (since the elevator is tens of thousands of kilometers long the percentage increase is tiny) and no major damage is predicted.
  • It is also possible that a private entity (risks notwithstanding) could provide the financing — several large investment firms have stated interest in construction of the space elevator as a private endeavor.

[edit] Cable Lean

The article states: At a 200 km/h climb speed this generates a 1 degree lean on the lower portion of the cable.

I don't understand how it could ever be that large. Given the enormous tension in the cable, the lean angle would be less than one arc-minute according to my back-of-the-envelope calculations. Before I jump in there and incorrectly fix that tidbit, can anybody give a derivation or a source? --Ctillier 05:42, 19 April 2007 (UTC)


"angular momentum (horizontal speed)" Angular momentum is not horizontal speed. Maybe this should say "(related to horizontal speed)" or "angular momentum and hence horizontal speed". —Preceding unsigned comment added by 203.217.67.58 (talk) 05:17, 6 June 2008 (UTC)

Horizontal speed implies significant angular momentum in this case (v*r where r is the distance from the centre of the Earth).- (User) WolfKeeper (Talk) 10:26, 6 June 2008 (UTC)

[edit] Speed of Climber

The article doesn't really say much about the speed of the climber, except for the non-specific 200 km/h mentioned above. For that matter, should we have a separate article article on the climber? --WhiteDragon 01:48, 26 April 2007 (UTC)

The final speed has not been decided yet. The climbers that build the Space Elevator are probably limited to 200 km/h, depending on how extra ribbon is added. The cargo and passenger climbers may be able to go at 1000 km/h once above the atmosphere. The limiting factor is wear on the bearings in the motors and wheels. Andrew Swallow 09:27, 26 April 2007 (UTC)

FWIW the speed is limited/determined by the power beaming system and is proportional to power (it's basically mgh). I think 1000 km/h is not achievable.- (User) WolfKeeper (Talk) 07:01, 26 February 2008 (UTC)
At 1/10 (height 13000 km) or 1/20 gravity (19000 km) mgh is not much of a restriction. Although gravity will be a big restriction near the Earth's surface.
For the first few hundred kilometres air resistance also restricts the speed. Andrew Swallow (talk) 06:13, 2 April 2008 (UTC)
No, not so much at these speeds. The other problem at altitude is that the power beaming doesn't work so well, I think the laser misses the panels somewhat and efficiency goes down. Stuff like that. There's information about it in the conferences notes that you can find online if you're interested.- (User) WolfKeeper (Talk) 17:01, 5 April 2008 (UTC)

Another limiting factor is also the shock waves of the lifter's contact with the ribbon within the ribbon itself. --64.81.163.182 19:37, 4 June 2007 (UTC)

IMHO that's unlikely, the speed of sound in the ribbon is very high, so the climber wouldn't generate shockwaves since it travels more slowly than the sound.WolfKeeper 03:14, 5 June 2007 (UTC)

It would, however, have a big effect on the oscillatory behavior of the ribbon. That's quite complicated, however, and we can't really say much about it until actual design specs come along. siafu 01:02, 13 June 2007 (UTC)

[edit] A few comments on the article

Good article overall, but in reading through it I think that certain areas are in need of improvement. Firstly I thought there wasn't really enough explanation of why it would be preferable to build a Space elevator. The economics section has info on costs and all, but this is rather brief and comes towards the end of the article, I would think that explaining the perceived necessity of such a device would be one of the first things to state.
There were some things about the specifics of the engineering which I think need a lot more explaining, for one, is it proposed that the cable be a single thick wire or many tiny thin ones? It seems to be talked about at various points as if it could be either, so I think that needs more clarity.
Something quite important that I don't think was addressed at all (or at-least I couldn't see it) was the issue of how exactly the cable (or the whole structure) actually gets up into space in the first place. Are we to assume that the cable will be towed up by a rocket or something? If not that, then how?
Several times in the article it is mentioned that the "Counterweight", could be an asteroid or a space station. But these two things are very different aren't they? I mean in terms of mass, an asteroid probably weighs millions if not billions of tons, whereas a manmade space stations would be only a few hundred or thousand tons (unless some gargantuan station is proposed). So how can these to things be comparable? And what kind of actual weights will be involved?
Finally the article doesn't give much information on how the climbers are proposed to move. It is mentioned further down that Magnetic levitation might be used, but is that the norm, is that what they all propose? Or are there different plans, like just mechanical wheels, etc?
Well that's about all I can think of for now, I hope the article can be improved with some of these suggestions. --Hibernian 00:00, 13 June 2007 (UTC)

It's been a while since I posted this, so can no one provide any answers to the questions I was asking? I think it's needed, if not for myself, then for the article. --Hibernian 23:22, 14 July 2007 (UTC)

I am not an expert on the subject but seeing as no one else has adressed your questions I will try. I assume it will get into Space like the ISS, in pieces and assembled in space. An asteroid can be any size at all. For the third, you might want to read the source.10max01 23:31, 14 July 2007 (UTC)

The plan being put forward by Liftport involves the cable being sent into orbit before deployment, in pieces; the plan you find in many sci-fi/futurist sources involves snagging a small asteroid and building the cable out it. The former is rather more realistic.
The two types of counterweight are equivalent due to conservation of angular momentum. The "space station" type counterweight requires much more cable, placing the counterweight a distance of 4-5 times further out than geosynchronous orbit. A large mass, like an asteroid, could be located closer to GEO. Again, using an asteroid is much science fiction than realistic possibility, but they do come in many sizes as noted by 10max10.
Lastly, different types of climber propulsion have been proposed. The Tether Challenge, one of NASA's Centennial Challenges, involves coming up with an effective way propel climbers using beamed power. Magnetic levitation sounds nice, but is rather pie in the sky, as evidenced by the fact that none of the Tether Challenge robots have used it. More likely very large rollers or somesuch would provide propulsion. siafu 00:32, 15 July 2007 (UTC)

Your answer seems pretty adequate.10max01 00:37, 15 July 2007 (UTC)

Ok thanks for the responses. So is any of this going to be put into the article? As my main compliant was that the article didn't explain these things adequately. --Hibernian 02:42, 17 July 2007 (UTC)

86.137.107.103 19:18, 29 September 2007 (UTC)== Cable taper plot ==

The cable taper plot shows a wildly different area ratio at GEO to that quoted in the text for steel (about 1.8 versus about 10^14). What assumptions is the plot is making about the type of material used? Are these in any way reasonable? I think that this discrepancy needs to be explained in the article. Matt 13:06, 6 August 2007 (UTC).

Using a value of 2GPa for the tensile strength of steel and density of 8000kg/m3, the equation says that the area at geostationary orbit should be on the order of 10^80 (area at ground level of 1cm2). Unless my arithmetic's gone wrong, I think that the thickness at GEO for steel should be changed. Concerning the taper plot, the inverse strength-density scale isn't all that useful - most materials seem to have inverse strength density ratios of orders of magnitude lower than this, so the ratio Area/Ao would be orders of magnitude higher for most materials. Essentially, the cable taper plot is correct, but not particularly useful - if anyone knows how to extend it for other materials, that'd be very useful. Template:Mark86.137.107.103 19:18, 29 September 2007 (UTC)

[edit] Towers

The notion that removing a few km of cable from the bottom of the elevator makes for great savings is just wrong. According to a very simple finite element analysis spreadsheet by Bob Munck (available in the yahoo group), the bottom 100 km of a 20 ton payload elevator weigh just ~400 kg. So, by building a 100 km tower you will save ~2% of capacity, or 2% of cable material. I would call that insubstantial, compared with the expense and plain impossibility of such a tower. The problem here is that antiquated notions from the earlier SE work (towers, asteroids, etc. etc.) which have since been outdated by Edward's work have somehow lodged within this article and need to be cleaned up. I suggest removing most references to towers or elevated locations except for one place where this is explained. Andreas 06:21, 13 June 2007 (UTC)

[edit] Helium Balloons.

I am aware of No Original Research, though I reckon that it must be the case that someone has already published what I am stating here, and hence that the information is citable. But, would strategically placing Helium Balloons at certain points along the tether aid the feasibility of creating the elevator? I believe that this might be so as the tension along certain points of the tether would be reduced via the use of such balloons (they would relieve the tension of the tether from under it's own weight at several strategic points along the tether). However, this is only something that could be done up to a height of about 20 miles up (the height to which most helium balloons will go. You might be able to squeeze out some more height using Hydrogen. It may even be possible to create several mile high rigid `floating structures' attached to helium/hydrogen balloons that could support the tether 30 miles up or so by attaching so structures to such balloons. Nevertheless, I remain pessimistic that the (600 mile?) barrier for fully fledged space access is traversible from such meagre heights (though, in actuality, this outlined approach might be more feasible than the space elevator AND overcome a significantly large proportion of the energy costs requires for getting into space).

If I have made an error in my reasoning, I would sure like to know.

Also, perhaps (solar powered?) magnetic sails (that force against the Earth's magnetic field) could be used to reduce the weight induced tension along several points of the tether? Perhaps more conventional thrust generation methods would relieve the tension allowable for a greater flexibility in material utilisation?

A general point could be that the space elevator doesn't really need to take up into space at all in order to be economically viable – it just needs to get us 10% of the way up (aren't most of the energy hurdles in relation to leaving the Earth's gravitational field used up in making the first small proportion of the distance?).

I have not done any calculations when making this post – though I do believe that the approximate figures given are unlikely to be terribly incorrect in principle at least.

ConcernedScientist 01:22, 30 June 2007 (UTC)

It's a reasonably good idea, but this isn't the place to discuss it.WolfKeeper 17:47, 14 July 2007 (UTC)
I concur. Though, with hindsight, I would refer the reader to Talk:Space elevator/Archive 6. Here, the balloon idea was already mentioned. I am not aware of any mention having been made concerning using high current conductors attached to the tether to induce a force due to the Earth's magnetic field (I know, the earth's magnetic field is probably only (0.3/16) Tesla's at any real appreciable distance from the surface - but it should still be feasible to generate a decent force capable of reducing tension within the tether so that carbon nanotube material isn't needed at all.

(Consider F=BIL, and a long superconductor on a moving air based platform to see that Carbon Nanotubes might not be absolutely necessary).

Anyhow, forgive my rambling, all of this is probably WP:NOR bound, so I'll stop making a mention of these ideas (though I doubt that they're Original Research as they are so obvious that someone must have posted them some time ago...).

ConcernedScientist 00:59, 15 July 2007 (UTC)

I believe balloons will not significantly improve the economics of the Earth/GSO cable configuration. Cable materials can be characterized by the length of a uniform cable that can just sustain itself against gravity without breaking, essentially l = (T/(g*rho)), if l is the characteristic length, T is breaking tension, g is acceleration of gravity, and rho is cable material density. For a tapered cable near the surface, the area must grow by a factor of e every time you go upwards by l. If I recall, l is on the order of 10 km for ordinary steel cable.

Unfortunately, the effective potential height of the Earth's gravitational potential well is about 5,500 km (again "if I recall"). So for steel we get an awful factor, of exp(5500/l) = exp(550) or so. This effective potential is the depth of the gravitational energy well of the Earth (which is just the radius -- about 6380 km for Earth -- for any spherical planet, since the 1/R^2 force's potential is -1/R) after taking into account the opposing centrifugal force, integrated from the surface to GSO. So, it reduces the problem from about 6380 km to ~5500 km, not a huge effect.

Near the surface, the gravitational acceleration is g ~ 9.82 m/s^2, so the potential height is essentially the same thing as the geometric height, 1 km per km. Thus what kills you is the region between the surface and 1 radius or so, where you have the bulk of the effective potential height that has to be overcome. Because the atmosphere is thin, scale height ~10 km, balloons won't work high enough (50 km is about their limit) to have much of an effect (just as shortening the cable by say, 50 km, so that the end dangles above the atmosphere, does not really help either).

The good news in the horrible exponential is that, IF you can find a material with a much better l, you can get a colossal reduction in the mass and a corresponding improvement in the economics. As far as I know, single-wall carbon nanotubes have the best l known to date, I believe the figure is over 1,000 km. Unfortunately, they are not yet available in quantity with uniform quality and sufficient length. I believe spinning such fibers into multi-strand yarns or cables is probably the way to go, but as far as I know it is still just an exciting possibility.

A comment here from someone in July 2007 attacked carbon nanotubes, but (while I am by no means an expert) the theoretical l numbers measured for some of them seem to make them the material of choice. I will try to provide better documentation from the literature as soon as I can, if it has not already been done by someone else. (Being new to this article I need to read it all carefully, and the discussion too.) Wwheaton (talk) 08:15, 18 December 2007 (UTC)

[edit] Interested Companies?

In the article, mention is made that companies or consortiums have already expressed interest in constructing a space elevator. I was curious if the major contributors or anyone had a list on hand of these companies/consortiums and the sources for the claims. It would be very interesting to check out the extent of big business' knowledge or interest in/of the space elevator idea--Meowist 21:30, 21 July 2007 (UTC)

LiftPort changed their estimated date for completing a Space Elevator from 2014 to 2031 after preparing a detailed plan. The new date is on their website. The article was changed to reflect the later date but has been changed back to the out of date value. I believe the article should say 2031. Their roadmap is in this document: [7]

Any comments? Andrew Swallow 10:57, 14 August 2007 (UTC)

LiftPort has run into major money problems, so predictions about them may need removing from the article. Andrew Swallow (talk) 06:16, 2 April 2008 (UTC)

[edit] Power source for climbers

The article states 'Chemical energy storage (batteries, fuel cells or internal combustion engines) will not work- hydrogen/Oxygen is the chemical fuel with the best energy/mass ratio, but will not lift its own weight all the way to GEO.'. However, rockets do so successfully, by dumping the waste product (water) as they go, so it doesn't have to lift it's own mass. Why would the climber need to hang on to its waste? Modest Genius talk 19:50, 13 September 2007 (UTC)

It doesn't. But the cable is weakest at the ground which limits the 'takeoff' mass, so while reducing the weight of the climber up the cable in that way would get some payload to the top, the percentage would be very small, and the climber would be highly inefficient.WolfKeeper 23:25, 13 September 2007 (UTC)
Oh I'm not saying it would be easy or efficient, but it wouldn't be impossible as that statement suggests. Modest Genius talk 23:39, 13 September 2007 (UTC)
I think that you would get something like 1/4 to 1/8 of your starting mass to GEO- IF you assume 100% energy efficiency and hydrogen/oxygen which has the highest mass-energy density. However, allowing for say using a small gas turbine to burn it, and 50% efficiency (which would be *really* good in fact), it's now actually about a 35:1 ratio, which implies multiple stages of vehicle. (This is also assuming I have my numbers right- LH has energy density of ~140MW/kg, stochiometric burning involves 1:4 LH to LOX ratio, energy to GEO is 50MJ up an elevator- and I think I'm right that mass ratio is exp(total energy needed per kg/energy per kg)). Doesn't look like it's a goer. Hope this helps.WolfKeeper 23:58, 13 September 2007 (UTC)


Why cannot the energy be transmitted without mass, eg., via auxiliary HV electric lines? I see no fundamental reason that energy itself cannot be transported masslessly, either up (from the surface) or down (from GSO), beyond the obvious (E/c2)  limit, which is surely negligible and irrelevant in the Earth/GSO context (as it would not be if Earth were a black hole, say). Other obvious possibilities would be light or microwave beams. This would of course entail sliding contacts (as on electric railroads), inductive coupling, or antennas, or whatever, but it does not seem fundamentally problematic.

There must be an engineering limit on the power rating of a conductive cable that would not overload the structure, which would be an interesting thing to consider. Has anyone looked into that? Wwheaton (talk) 22:59, 12 January 2008 (UTC)

Conducting power via copper cables would add about 3 kg/m (way too much to support) and there would be unacceptable power loss over such long distances. Only superconductors would work and the cable itself would have to be made from them to keep the wieght down.

There is a citation for the statement that nuclear and solar power is not feasible, the link does not work. Solar power IS feasible above the earth's atmosphere. See description under Climbers at http://www.liftport.com/wiki/id,space_elevator/ --Innov8tor (talk) 17:17, 20 April 2008 (UTC)

So in conclusion, I'm removing this. It's a silly unsourced statement. Rockets can reach geosynchronous orbit with chemical energy, so too can space elevator payloads. It's a silly thing to do, but not impossible as the thing implies without careful inspection.
Further, this is Original Research but in this mystical world where we have no problem manufacturing carbon nanotubes of arbitrary length, they can also be configured to serve as semiconducting wire, but I like the laser idea better anyway. -Verdatum (talk) 10:20, 29 May 2008 (UTC)
The cited reference does not agree with your text. In the reference they are talking about moving the initial elevator to GEO prior to deployment of the cable down to the surface.- (User) WolfKeeper (Talk) 13:21, 29 May 2008 (UTC)
Basically, chemical powered climbers isn't practical in any known way. The energy needed per kg at GEO is too great.- (User) WolfKeeper (Talk) 13:21, 29 May 2008 (UTC)
Aha, I was reading too fast. Thanks for the catch. -Verdatum (talk) 14:11, 29 May 2008 (UTC)

[edit] Image incorrect

I replaced the SVG diagram of the elevator with the original PNG one, because the SVG showed the elevator to go up from the north pole, which is nonsense. Many people don't intuitively understand why it has to go from the equator, because many don't understand the idea of an orbit. 79.120.55.7 07:01, 20 September 2007 (UTC)

I'm glad I wasn't the first person to catch this mistake. But it looks as though it's been reverted to the SVG. The caption mentions a geosynchronous orbit but the picture does not reflect it. I was so surprised I had to go back and check my physics ;) -Verdatum (talk) 18:21, 27 November 2007 (UTC)
OK, I fixed it, as well as various other places that were linking to the same image. -Verdatum (talk) 18:50, 27 November 2007 (UTC)

[edit] Failed verification tag for Smitherman

In the "Construction" section, there is a reference to "Five Key Technologies for Future Space Elevator Development". The Smitherman paper mentions 7 low-TRL areas, which don't match up with the 5 in our article (Smitherman doesn't mention towers for example, but they feature in several of ours). Perhaps there is another NASA study from which those 5 were taken. Kingdon 23:03, 9 October 2007 (UTC)

[edit] New developments

Pulled from the LiftPort forum.

"The University of Cambridge will announce that it has produced 20 Gpa carbon nanotube ribbons

"Recently, Dr. Alan Windle at the University of Cambridge announced the development of 20 GPa yarns derived from nanotubes. These materials are produced from nanotube yarns and contain graphitic hyperfilaments composed of nanotubes, which exhibit strengths comparable to an individual nanotube but over macroscopic length scales."

Since I know something about the topic, I can't edit the article due to WP:COI under the current policy. So if there is someone watching this who can get away with editing this article, please do.

This is probably strong enough for a reasonable step-taper, moving-cable design, about ten years before I expected it to be available. Keith Henson (talk) 02:24, 17 November 2007 (UTC)

IRC That's not strong enough, by at least a factor of 2 and probably 4. The minimum practical taper seems to set the value at about 40 GPa and you need to allow for an additional safety factor of some number, like 2 on top of that.WolfKeeper (talk) 04:04, 17 November 2007 (UTC)
A pascal is 1 kg·m−1·s−2
Density assume about 1340 kg m-3
So 1340 kg m-3/20,000,000,000 kg·m−1·s−2 x 4.832 x 10,000,000 m2 s-2 (Units check)
= 3.23744
10 ** 3.23744 which is about 1727. That's a bit high I agree.
40 GPs would be
10 ** 1.61872 which is about 41.6. That's within the moving cable area--perhaps. Keith Henson (talk) 01:40, 18 November 2007 (UTC)


Recent report (Krzysztof et al., Science, 21 Dec 2007, vol 318, p 1892) from the Cambridge group shows specific stress (GPa/SpecificGravity) for multi-CNT fibers of up to about 9 GPa/SG, for about 1 mm lengths, with lower values for longer fibers. This they attribute to the statistics of defects and dislocations along the fiber. Wwheaton (talk) 02:04, 13 January 2008 (UTC)

[edit] Possible typo

"In an ideal cable, the actual strength of the cable at any given point would be no greater than the required strength at that point (plus a safety margin). "

Shouldn't it say less than?

It's correct this way, but perhaps not obvious. Strength in excess of the minimum comes at the cost of mass, and excess cable mass is a killer in a space elevator design. Keith Henson (talk) 14:45, 18 November 2007 (UTC)
Clearly the actual strength can't be less than the required strength at a given point! So taken together, "no greater than," and "not less than," means "equal to".

[edit] Missing discussion of technical problems

Good article, however a discussion of the reasons why an elevator isn't being built right now is missing. What challenges are ahead? Are there any problems associated with making the ribbon? The article primarily deals with what an elevator would look like, if it was there. -- Oz1sej (talk) 10:32, 23 November 2007 (UTC)

[edit] 20GPa is a dubious claim

There are two websites stating that Professor Windle has made this claim. However, they are both groups with an axe to grind (one a company involved in making carbon nanotubes and the other a space elevator enthusiast site). I can find no other report of this figure despite quite comprehensive coverage of Dr Windle's paper elsewhere. As such we should treat this as hearsay until someone comes up with a credible source for this. I am removing the claim pending a better source being found. Barnaby dawson (talk) 13:34, 12 January 2008 (UTC)

Further correspondence with Professor Windle I can confirm that he has not claimed to have produced carbon nanotube fibres of 20Gpa in strength (his actual claims can be found in his paper (Science: 21st December 2007, vol 318, p 1892)). He believes (and I think it highly likely) that these 20Gpa claims are just rumours brought about by wishful thinking. So lets make sure we're more careful in future not to report hearsay without checking first with the source! Barnaby dawson (talk) 09:00, 15 January 2008 (UTC)

[edit] Broken Links

Could someone try and re-discover the actual locations of many of the links? —Preceding unsigned comment added by 86.134.117.43 (talk) 15:05, 2 February 2008 (UTC)

Agreed, citation #32 to the WVHTC is broken. They re-arranged their site. And I'd like to know why solar power won't raise a load in "reasonable" time. 64.238.49.65 (talk) 16:27, 22 February 2008 (UTC)

Here are a few updated links: http://www.spaceelevator.com/docs/472Edwards.pdf http://www.spaceward.org/elevator2010-faq http://www.liftport.com/forums/index.php?topic=387.0 —Preceding unsigned comment added by 63.211.201.174 (talk) 09:19, 18 March 2008 (UTC)

All animation links are broken. —Preceding unsigned comment added by Ralfx (talk • contribs) 07:49, 10 May 2008 (UTC)

[edit] some revisions

(1) deleted mention of Tesla. Unless somebody can find a citation stating Tesla's invention of the space elevator, this is just gossip. (2) of course Tsiolkovsky's notes were "behind the iron curtain." Tsiolkovsky was Russian. This goes without saying.

Besides being anachronistic--Tsiolkovsky's conception of the tower dates from ca 1895, long before the Iron Curtain metaphor was invented at the end of WW II. Wwheaton (talk) 21:23, 21 February 2008 (UTC)

(3) deleted statement "and without the substantial environmental harm caused by some rocket fuels." This seems to be an un-called for editorial, and, the obvious way to avoid the harm by "some kinds" of rocket fuels would be to use "other kinds" of rocket fuels; you don't need a space elevator to do this. —Preceding unsigned comment added by 76.228.107.157 (talk) 02:33, 21 February 2008 (UTC)

[edit] Carbon nanotubes strength

"[in ref to tensile strength] ...carbon nanotubes[28] can reach upwards of 20 GPa" "[carbon nanotubes] observed tensile strength has been variously measured from 63 to 150 GPa"

These two sentences come right after another and confused me. I'm sure they aren't contradictory, and mean slightly different things, but it isn't made clear exactly how they differ.--91.125.161.170 (talk) 01:08, 26 February 2008 (UTC)

I expect some of the others who are better up to date than I can give a better answer, but I'll make a stab at it and let them correct me. First of all, there is the fact that there are different subtypes of nanotubes: single-walled and multi-walled, and also different pitch classes (the way the fundamental graphene sheets are laid w/r to the axis). Then there is theoretical strength vs strength measured in the lab. Also there are differences between single elementary tubes grown in the lab which have various lattice imperfections that may create weaknesses every now and then, depending on the length of the tube and the density of dislocations. Finally, even if the single tube has a weakness every 10 um, say (diameter might be 1000 times less than that), one may be able to twist elementary tubes together as cables or yarns somehow, so that stress is transfered from tube to tube every 0.1 um, and the composite cable is only a bit weaker than the tubes that compose it. Obviously there are many conceivable ways to do this sort of thing, and investigators have been working, trying to grow elementary tubes that are longer and more perfect and uniform, and twist them into yarns or whatever, with the aim of making fibers or cables, whatever you want to call them, that are long, capable of manufacture in reproducible quantity, and free of defects that compromise the strength of the whole, while maintaining the low density that is essential for the space elevator application.
The theoretical strengths of perfect tubes I believe are up in the 100 GPa region, or even a little higher. That sets an upper limit to what can be actually done in practice. One group lately reports yarns with strengths approaching 10 GPa (~100,000 atmospheres) for lengths of about 1 mm, I believe it is. Obviously we have a long way to go to GSO, but the various methods of producing fibers, the changes in the state of the art with time, etc, account for the differences (plus fairly frequent confusion amongst us fallible ignorant humans about the precise meaning of the numbers thrown about). It would be very nice if we had a graph versus time showing the state of the art for the various kinds, but these things are potentially of such wide technical use and economic importance that the place to put it would be in the carbon nanotube article, where in fact we have a table that helps a lot. That article is maybe the place for us onlookers to start getting educated. Wwheaton (talk) 04:56, 26 February 2008 (UTC)
Thanks for the info, a very interesting reply. I still think the two lines need clarifying or rephrasing on the main page.
The way it reads, it says to me "The maximum theoretical strength of CN is 20GPa. CNs have been produced with a measured strength of 63-150 GPa". Obviously this interpretation is incorrect, but I can't see what the correct interpretation is.
Was the difference theoretical vs observed? Was one talking about an individual tube and the other about threads?--217.18.21.2 (talk) 13:13, 26 February 2008 (UTC)

[edit] Style

WP:MOS has nothing to say about rhetorical questions to the reader, but the tone of this paragraph sounds slightly informal and non-encyclopedic to me:

Assuming a multi-national governmental effort was able to produce a working space elevator, many political issues would remain to be solved. Which countries would use the elevator and how often? Who would be responsible for its defense from terrorists or enemy states? A space elevator could potentially cause rifts between states over the military applications of the elevator. Furthermore, establishment of a space elevator would require removal of existing satellites if their orbit intersects the cable (unless the base station itself can move in order to make the elevator avoid satellites, as proposed by Edwards).

I can think of no correction that would be definitely better, but perhaps something like the following would be more formal: "Two of the most important issues are ownership and usage of the elevator, and its defense against terrorist attack." --- Arancaytar - avá artanhé (reply) 11:02, 19 March 2008 (UTC)

[edit] Reverted subsection "Gris Bosque's proposal"

Dear Nforest, Excuse me, but I just reverted your material re using geothermal energy, because it seems at first glance to be technically nonsensical. The main thing is that, just as the Earth's atmosphere is held tightly to the surface by gravity, so any gas in a pipe would also be held. (The exponential scale height for air is 7 to 10 km below 100 km or so, above which it gets very hot and so is longer. Given that the effective potential height to GSO is around 5600 km, that would be 560 e-folds for air, 40 for H2 at room temp, 10 for H2 at 1200 K; this latter would reduce the density by ~22,000.) It could of course be pumped up, but that would require power, and I am essentially certain that would take more energy than it could carry if the temperature were low enough not to vaporize the containing pipes. A secondary point is that because of the abundance of solar energy, I am convinced that energy is not likely to be a big problem in space in the neighborhood of the Earth. And also because, if energy is needed from the ground, it can first be converted to electric power and sent up, with less weight overhead than any piped system is likely to have.

This all slightly hand-waving, so other editors may want to comment, but I think it should be reverted at least temporarily. Wwheaton (talk) 19:39, 26 May 2008 (UTC)

I thought your explanation that it's unreferenced OR was a bit long winded Mr. Wheaton ;-)- (User) WolfKeeper (Talk) 20:45, 26 May 2008 (UTC)
Probably so: I did not have time to check out the web link, but I thought it incorrect. I like to here myself yak, no doubt. Beg'n yer pardon, sir!  :) Wwheaton (talk) 04:01, 27 May 2008 (UTC)