Talk:Space elevator/Archive 7

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 $$m g h$$). 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)

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: 

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

What if you combined the elevator is space-based solar power. Massive solar panels in space transmit back down the tether. There could be contacts along the tether which the climber could use for power. The excess power goes in to the power grid on the ground. 64.201.165.253 (talk) 20:52, 18 July 2008 (UTC)Larry

Typo?
In the "Cable" section it says and even a space elevator that did not reach GEO would have a mass of 20,000 kg. This must be a typo, right? That would suggest less than 1kg per kilometre of cable, or less than 1 gram per meter. Can someone check this number. Fig (talk) 19:27, 18 July 2008 (UTC)


 * No, that's correct (although it sounds a bit garbled), Brad Edwards has proposed a minimal initial tether of about that mass per km.- (User) WolfKeeper (Talk) 21:48, 18 July 2008 (UTC)

Tower of Bable.
Why is the temple of babble not mentioned as one of the first space elevators? PS. yes i know it is just mythical. —Preceding unsigned comment added by 69.149.222.65 (talk) 04:18, 24 July 2008 (UTC)

That would be a different article. Also it is not an elevator, but a tower. This article focuses on Powered space elevators, so I think the lack of power would disclude it.Mech Aaron (talk) 19:01, 29 September 2008 (UTC)

Elevator Access
Is there discussion on elevator access? What happens when the elevator stops at Space Station altitudes for a crew shift change for example. Because the elevator at Space Station altitude is travelling at about 1/720 orbital velocity, the astronaughts will need to immediately accelerate to near Escape Velocity when they step off into space. Otherwise they will drop back to Earth and burn up in about 15 seconds.Wyatt arp (talk) 04:36, 11 August 2008 (UTC)


 * The plan is not to stop there, they don't plan on stopping till they get to geosynchronous orbit. However, you could carry a biggish rocket with you and launch to orbit from LEO altitudes. Because you're higher up, the rocket is *much* smaller than it would be from the Earth. However, there is a safety risk in carrying live rockets up the cable.- (User) WolfKeeper (Talk) 15:27, 11 August 2008 (UTC)

Space elevators don't exist, therefore nothing happens when they have an (imaginary) shift change!Yobmod (talk) 17:56, 11 August 2008 (UTC)
 * But the ISS does exist, and does have crew changes, which is what the question was about.
 * —WWoods (talk) 21:27, 11 August 2008 (UTC)


 * Confused! ISS isn't mentioned in the question at all, and it has no interactions with the (non-existant) elevator.Yobmod (talk) 13:57, 26 September 2008 (UTC)

Tags
My fact tags and removal of uncited matierial was reverted, without an edit summary. Why? The sentences are clearly uncited, so need fact tags - they mostly look like original research by a student with too much time on their hands. If no source exists that says this about space elevators, then nor should this article. If the sources do exist, then add them - but don't delete tags!Yobmod (talk) 14:26, 29 August 2008 (UTC)


 * Let's just say that I look unfavourably on edits that remove accurate information based on wild, derogatory speculation about who added it, irrespective of whether it happens to be referenced or not. Please read and follow WP:CIVIL.- (User) WolfKeeper (Talk) 14:57, 29 August 2008 (UTC)


 * Is being a student derogatory now? lol! Guess i should de-matriculate. And you reverted before i posted here, so that cannot have been your reason. The information i deleted may have been accurate, but it was both uncited and in far to much detail for this article. Explaining the physics of falling objects (in 3 paragraphs!) is beyond the scope of this article - it is already on the long side, no?Yobmod (talk) 08:04, 1 September 2008 (UTC)


 * If you don't consider "they mostly look like original research by a student with too much time on their hands" to be derogatory, yes.- (User) Wolfkeeper (Talk) 23:53, 26 September 2008 (UTC)

" If the initial height of the object falling off of the elevator is less than 23,000 km, its orbit will have an apogee at the altitude where it was released from the elevator and a perigee within Earth's atmosphere &mdash; it will intersect the atmosphere within a few hours, and not complete an entire orbit. Above this critical altitude, the perigee is above the atmosphere and the object will be able to complete a full orbit to return to the altitude it started from. By then the elevator would be somewhere else, but a spacecraft could be dispatched to retrieve the object or otherwise remove it. The lower the altitude at which the object falls off, the greater the eccentricity of its orbit.

If the object falls off at the geostationary altitude itself, it will remain nearly motionless relative to the elevator just as in conventional orbital flight. At higher altitudes the object would again be in an elliptical orbit, this time with a perigee at the altitude the object was released from and an apogee somewhere higher than that. The eccentricity of the orbit would increase with the altitude from which the object is released.

Above 47,000 km, however, an object that falls off of the elevator would have a velocity greater than the local escape velocity of Earth. The object would head out into interplanetary space, and if there were any people present on board it might prove impossible to rescue them."


 * Why can't ALL of this be replaced with one sentence. "Objects falling of the tether will obey the laws of physics, see articles xxx and yyy."? and why are they immune to policies instructing editors to avoid original research and cite one's sources? btw, i tagged it but didn't delete. Yobmod (talk) 08:31, 1 September 2008 (UTC)


 * Because objects falling off the elevator above GEO fall [B]up[/B] instead of down. Most people find this behaviour unexpected, unexpected behaviour needs documenting.  Using the elevator as a interplanetary sling by releasing objects above 47,000 km is a special property that also needs including in the article.  The information exists on websites. Andrew Swallow (talk) 08:21, 20 September 2008 (UTC)


 * Websites that are reliable sources for science articles? If they exist, why aren't they used as cites?Yobmod (talk) 08:54, 22 September 2008 (UTC)

At the moment the article is loaded with unverified claims bordering on original research. Too many mays and coulds. Much of the text is also way too technical. Remember this is an encyclopedia for a general audience. 203.7.140.3 (talk) 08:32, 24 September 2008 (UTC)
 * Which claims, exactly? Reyk  YO!  08:36, 24 September 2008 (UTC)


 * For example the claims that are tagged in the article - have you read the atrticle? I copied some above. Such as: "By then the elevator would be somewhere else, but a spacecraft could be dispatched to retrieve the object or otherwise remove it. The lower the altitude at which the object falls off, the greater the eccentricity of its orbit."
 * Makes 2 distinct specific claims, both need cites. (btw, the IP is not me)Yobmod (talk) 11:08, 24 September 2008 (UTC)
 * Well, it's unreferenced, but the basic physics seems sound.- (User) Wolfkeeper (Talk) 23:53, 25 September 2008 (UTC)
 * Ah, the basic physics of the hypothetical space craft? What about the basic economics? Or the assumption that such space craft will be available for rescue missions at all? Why would this apply at all if climbers were powered? These ideas need to be attributed to a reliable source, not to an anonymous WP editor.

Wikiprojects associated with this article have downgraded the rating to C. In the case of Wikiproject Economics it was downgraded from GA to C. That's quite a fall! As it reads the article is highly speculative. Start improving it by removing the original research, unpublished synthesis and science fiction. 59.167.49.189 (talk) 11:18, 25 September 2008 (UTC)


 * I remove OR wherever there is some that I have spotted, and I've read most or at least a representative example of the technical papers and conference proceedings that are available. There's a difference between OR and unreferenced a mile wild and a mile deep. The argument that there wouldn't be spacecraft if climbers are powered makes no sense whatsoever to me; that appears to be OR.- (User) Wolfkeeper (Talk) 03:33, 15 October 2008 (UTC)


 * Did it ever even go through Good article review? Looks like someone thought losing featured status = automatic GA, which it doesn't. C or B seems right.Yobmod (talk) 12:03, 25 September 2008 (UTC)


 * I've read a lot of the research papers on Space Elevators. So far as I am aware there's no original research here, but there might (literally) be the odd sentence or two here and there that has snuck in since it was written. But AFAICT on every major point it's about bang on the published papers and conference proceedings.- (User) Wolfkeeper (Talk) 23:53, 25 September 2008 (UTC)

I have removed some of the "this article has issues" tags because they are entirely without merit: 1) The article is not too long. It contains less than 10,000 words (this naturally excludes images, image captions, footnotes etc), which by WP:LENGTH is a perfectly reasonable article length. 2) Nowhere does the article confuse fiction with fact. It deals with speculation about possible future technologies, but that's not the same thing. 3) Regarding splitting the article: No. Just no. Most of the various space elevator designs have their own articles already so there's nothing you can split it into. And it's not as though the article is too long anyway. Regards, Reyk  YO!  13:18, 26 September 2008 (UTC)


 * Hey, sorry for reverting - i checked the page and for discusion and reverted, but must have been too fast :-). Doesn't mean i agree though, here's why:


 * No probs. In future I'll type my response first and revert second to avoid this sort of thing. Reyk  YO!  23:04, 26 September 2008 (UTC)
 * 1) It is too long - not withstanding the word number (51K of readable prose is long!), as an intelligent reader with a scientific background, this article is simply too long to enjoy reading and concentrate on, mostly cos it goes into too much detail in some areas, and needs tighter writing in others. WP:LENGTH states Readers may tire of reading a page much longer than about 6,000 to 10,000 words, which roughly corresponds to 30 to 50 KB of readable prose. This article is more than the top end of this range!


 * If you copy and paste all the text in the article into something like Microsoft Word, and then do word count, you'll find it comes in at something like 9,500 words, which is perfectly fine. Many FAs have kilobyte lengths longer than 32k, such as Enceladus (63k), Australia (67k) and J. R. R. Tolkien (84k). It's the quality of the writing that is the issue here, not the quantity. Reyk  YO!  23:04, 26 September 2008 (UTC)
 * 2) The article often treats hypothetical ideas for construction as fact. They are not facts - they need to point out that. Most of the prediction herein will likely be wrong (and some are contradictory) so discussion of the ramifications must be clear about when it is based on real existing science (fact), or based on wishful thinking (fiction)


 * A hypothetical idea is not a fictional idea. The fiction tag, as I understand it, is mainly to indicate that a fictional subject is being dealt with in an in-universe style. So if I were to start an article with "General Bloggs is the commander of the Galactic Defense Force based on the planet Xebulak IV", that would be an appropriate use of the fiction tag. Describing hypothetical (but non-fictional) proposals without making it clear that they're still only speculative and haven't been realized yet isn't the same thing. I'd say that falls under or possibly WP:CRYSTAL.  Reyk  YO!  23:04, 26 September 2008 (UTC)
 * 3)If most of the designs have articles already, then this article only needs summary style sections. either these summaries need to be shorter (just explaining the design, and leaving arguements about them or possible problems to the sub-articles), or more sub-articles have to be spun out.


 * There's a big difference between hypothetical and proposed. This actually is a proposed structure. There are people that actually are trying to build it right now. And there are actually good reasons to think that they may succeed. Carbon nanotubes are actually strong enough (at the small scales). There's no generally accepted reason they can't be made big enough to do this. A true hypothetical structure is not something you can actually try to build.- (User) Wolfkeeper (Talk) 23:50, 26 September 2008 (UTC)


 * This article clearly has many problems - it's gone from Featured to C class! Do you really think it would have a chance at Good article nomination? The established editors here seem to want to maintain the status quo at any cost even though the article they are protecting has become poor under their influence. removing tags without adding sources doesn't improve the article. This subject deserves to have a featured article, and should have hundreds of sources to allow it to fly through GAN on the way.Yobmod (talk) 13:40, 26 September 2008 (UTC)


 * I don't think it does deserve to be featured article. It does deserve not to be vandalised by replacing dead links with OR tags and similar though.- (User) Wolfkeeper (Talk)


 * I hardly see how finding a dead link, finding the archive of the target, then asking about the source on the talk page is vandalism.Yobmod (talk) 07:23, 29 September 2008 (UTC)

Centrifugal Physics
From Wikpedia, the equation for centrifugal acceleration is w*w*R. Where w is the angular rate of rotation and R is the distance between the rotating object and the center of rotation. Centrifugal acceleration needs to be equal to the acceleration due to gravity or greater. From Wikpedia, the acceleration due to gravity is 9.8 m/s/s. The Earth is spinning at a fixed w of (2*PI/(24*60*60)) = .0000727 radians per second. From Wikpedia, the Radius of Low Earth Orbit is an altitude up to 2000000 metres. From Wikpedia, the Radus of the Earth is over 6000000 m. So Earth's Low Earth Orbit centrifugal acceleration is w*w*R = .0000000052885*(8000000 metres) = 0.04 metres/second/second. This is less than the 9.8 m/s/s required to overcome the acceleration due to gravity. The earth is not spinning fast enough for a tethered system. —Preceding unsigned comment added by Wyatt arp (talk • contribs) 03:51, 7 August 2008 (UTC)


 * OMG! You're right! All those Ph.Ds missed it, but you're much smarter!


 * Alas, it's such a shame, but we can't use it in the article, because it's 'OR'.- (User) WolfKeeper (Talk) 04:39, 7 August 2008 (UTC)
 * You're right about the OR, but there's no need to be snarky. Reyk  YO!  04:49, 7 August 2008 (UTC)


 * To clarify, centrifugal force and gravity balance at the height of the geostationary orbit. Below that the net force is downward; above that the net force is upward.
 * —WWoods (talk) 21:27, 11 August 2008 (UTC)


 * Mr Wyatt is correct. Contrary to popular opinion, and also contrary to what is stated in the article, a space tether does not rely on "centrifugal force", so centrifugal calcs will not give the correct result. The main operating principle is a satellite in geosynchronous orbit.
 * Centrifugal force doesn't really exist anyway.
 * —Bobcousins (talk) 20:51, 5 January 2009 (UTC)


 * Um... actually it does work to use that here since the Earth/space elevator is in a non inertial frame of reference. See Centrifugal force for more details. Whether centrifugal force 'exists' see:- (User) Wolfkeeper (Talk) 21:00, 5 January 2009 (UTC)

I just did the math (high school physics, not Particle Dynamics), and I got a geo-synchronous height of 42,000km. With better math I am sure I would get the agreed upon geo-synchronous height of 35,000km. So Check your math.
 * $$a_{cent}= w^2*R$$
 * $$a_{grav}= \frac{G*M_{earth}}{R^2}$$
 * $$R_{Balanced}= (\frac{G*M_{earth}}{w^2})^{(1/3)}$$

Mech Aaron (talk) 19:18, 29 September 2008 (UTC)


 * That's the radius of geostationary orbit — the distance from the Earth's center; the height above the Earth's surface is 6,378 km less, that being the Earth's equatorial radius. See Geostationary orbit.
 * —WWoods (talk) 23:34, 29 September 2008 (UTC)

Proposed cleanup
I've been following the debate and everybody seems to be getting bogged down in minutiae. Let's all take a step back and look at the big picture rather than getting into a edit war about what tags are and aren't valid. Dealing with the issues one by one.
 * Sources. If something has been published in a journal or proceedings, cite it as a journal article. Citing a web site always leads to questions about the credibility of the source. This also protects against link rot.
 * Length. Wikipedia's rule of thumb is "> 60 KB 	Probably should be divided". The length and the quality are linked as the article strays off onto tangents. Suggested division:
 * * Physics and structure: Way too technical. Suggest condensing this whole section into no more than a 3-4 paragraph summary and no more than one paragraph on each sub-section. Some could be split to Space elevator construction.
 * * Cable: There is a lot of overlap with Carbon nanotubes. Suggest condensing this whole section into no more than a 3-4 paragraph summary. Some could be split to Space elevator construction.
 * * Cable taper: The first paragraph is fine but nothing else is needed. I suggest splitting it off into a new article or link to the paper that came up with the equation. The equation is totally unnecessary.
 * * Climbers/counterweight: Seems okay but could be simplified a little
 * * Angular momentum, speed and cable lean: Too technical and unnecessary. A 1 paragraph summary and the diagram is sufficient for a general audience.
 * * Construction: Suggest a 1-2 paragraph overview and split to Space elevator construction. The fact that a company is now seriously proposing to construct one makes this notable in its own right.
 * * Failure modes, safety issues and construction difficulties: This is a very narrow aspect of the topic and goes into a lot of detail. Suggest splitting into Space elevator safety and Space elevator construction.
 * * Economics: A lot of this is already covered in Space elevator economics. Suggest migrating this whole section into that article and removing any overlap. Already linked as a "See also".
 * * Alternatives to geostationary tether concepts: This is straying a long way off topic. Since most of them already have articles, I suggest migrating these sections into the relevant articles and removing any overlap. They can be linked as "See also".

Comments? Cosmomancer (talk) 08:33, 27 September 2008 (UTC)
 * Original research and synthesis. I can see why this is being raised. From WP:SYNTH, "Material published by reliable sources can be put together in a way that constitutes original research. Synthesizing material occurs when an editor comes to a conclusion by putting together different sources. If the sources cited do not explicitly reach the same conclusion, or if the sources cited do not make this argument in direct connection to the topic of the article, then the editor is engaged in original research." The text needs to be very carefully examined to ensure the sources explicitly say the same thing as the text and there is no unpublished synthesis.
 * Tone. Parts of it read more like a term paper than an encyclopedia article.
 * Too technical. I agree that it is too technical for a general audience. Part of the reason seems to be it goes into a lot of detail about relatively minor aspects of the topic described above.
 * Fiction. I understand the issue being raised. If this article is to be taken seriously all mention of fictional space elevators should be moved into Space elevators in fiction and described in more detail there. Any non-fiction proposals similar to fictional descriptions make the fictional descriptions more notable, not the other way around.


 * Also the lead has a weird little paragraph appended to it. If sourced, maybe it should be moved? It currently makes the lead longer than recomended 4 paragraphs.
 * Splitting uncited sections from here into new articles is also problematic, only those long section with sources need to be summarised and spun off. Others should bbe trimmed back until the editors that want the information here present the sources that they used to write the sections, otherwise we get more articles like Space elevator economics]'', which has just the same problems as hereYobmod (talk) 07:24, 29 September 2008 (UTC)


 * I've made some bold edits that somewhat simplify the article with less wandering off topic. The new space elevator construction and space elevator safety can now be significantly expanded and improved without being too off topic from this article. Cosmomancer (talk) 12:55, 1 October 2008 (UTC)

Tags and Edits
It seems that a lot of the problem here is that we have editors who come into an article and tag it with problems, but don't do anything to fix the problems. It's easy to demolish, harder to rebuild.--2008Olympian chitchatseemywork 02:26, 28 September 2008 (UTC)


 * Don't be bullied by excessive tagging. 71.191.40.106 (talk) 05:10, 28 September 2008 (UTC)


 * Any attempt to delete uncited original research gets reverted. People have tried to improve the article, but cannot. Deleting off topic and unsourced information after a decent interval of leaving it tagged isn't demolition, it is good editiing. If people don't like the tags, replace them with sources!
 * Note, removing all the completely uncited paragraphs more tha halves the readable prose of thise page from 51Kb to 25Kb (see draft with OR removed)). An article of this length with so much unsourced text needs the tags to warn readers.Yobmod (talk) 11:53, 30 September 2008 (UTC)Yobmod (talk) 07:17, 29 September 2008 (UTC)


 * I see absolutely no consensus that this tag should be added, frankly you're in a minority of one. Given that, I consider this to be a deliberate, entirely excessive defacement of an otherwise averagely written and referenced article.- (User) Wolfkeeper (Talk) 18:56, 27 October 2008 (UTC)
 * Yeesh! When was the last time anyone actually did any work on the article? It seems like the two of you are more interested in arguing and edit warring about whether the big glaring template at the top is appropriate than in improving the article. Yobmod, if there's specific unsourced claims you could try to find sources yourself; or, ask Wolfkeeper, who seems to be clued up about space elevators. And please don't follow through with your threat of gutting the article, at least not until people have made an honest effort in sourcing it. And Wolfkeeper... there are vast tracts of unsourced stuff in there that need to be substantiated. You're adamant that the article more or less reflects the current state of things. Well, you must have read about this stuff somewhere- tell us where. Reyk  YO!  23:41, 27 October 2008 (UTC)


 * Look, all I'm saying is that the article has over 50 distinct reference tags to 46 distinct sources. If anybody wants to tag particular statements or sections fine-no problem-but adding 4 or 5 general tags to make claims about the entire article completely misrepresents the state of the article and is simply not what these tags are for; I could understand it if it had 10 references or something, but this is out of all proportion.- (User) Wolfkeeper (Talk) 01:26, 28 October 2008 (UTC)


 * Erm, you removed the citation needed tags i added, remember? And many others have added (diff ) But i still count 17 improvement needed tags in the article. Why not just add the cites, as you have read so much on the subject? I cannot add cites for things i have no sources for. Removing the citation needed tags, then claiming that the unreffed template is not-needed does not improve the verifiability of this articleYobmod (talk) 08:44, 28 October 2008 (UTC)

My original stated complaint was that there was tags without work to remove them, not that the tags were there to begin with. The work I've done on the article has focused on citing the statements in the article, as well as ensuring that the references actually support the propositions for which they stand. The tags are correct, the article was full of unreferenced statements, and still is to a great, if lessened degree. We should take advantage of the fact that this article's demotion from featured status gives it a chance to be in the spotlight of a renewed effort to resurrect it and point out what is wrong with the article to editors who come here in that spirit. I think the tags are accurate, and I note that there are a few less than when it was first tagged.--User:2008Olympianchitchatseemywork 09:38, 1 November 2008 (UTC)

I don't know the topic, but I know tag grafitti when I see it. "Defacing the article" is good, I'm going to remember that. Editing means writing - or helping writers to write better, which is why there are talk pages. I saw the offending paragraph and thought, "Ah, rhinocerous in a china shop!!" It's just a passive-aggressive way to argue without seeming to. "Who says so?!?!? Where'd ya get that?!?!?  EH,EH?!?!?" Editing is writing, or helping to write better, IMHO. Tagging means nothing - personally I wish they didn't exist at all - they're a lazy way of thinking you're actually doing something. Jjdon (talk) 20:40, 10 March 2009 (UTC)

Vandalism
I have requested temporary semi-protection from the anon IP vandalism. Cosmomancer (talk) 06:18, 11 October 2008 (UTC)

Unclear
The article does now mention that not all plans involve a geosynchronous target, but it still doesn't explain why the most popular ones do; or at least, I didn't see it. Can someone please add, if not in layman's terms then at least with some explanation, why the geosynchronous orbit is so important? Why can't the elevator end at much lower orbits, and just have a mobile or airborne platform at the bottom? Obviously if this were possible the entire materials cost would be reduced enormously, which is why it comes to mind; but like presumably many other readers I am not seeing why this intuitive solution is not practical. Someone help? Leushenko (talk) 12:56, 31 October 2008 (UTC)
 * Most designs call for a stationary cable, whether or not the lower end actually touches down. The only way this can be achieved is with geosynchronous orbit. There are proposals involving much shorter "flyby" cables in a non-synchronous orbit, but this opens another massive book of engineering challenges in terms of transferring cargo to the cable. Stationary cables are the only designs under serious consideration.--Yeti Hunter (talk) 13:48, 31 October 2008 (UTC)

Summary image
A while ago I replaced the current image with this SVG. It seems to have been completely shunned by Verdatum, stating "the vector version of the image is incorrect". Problems cited are: the elevator appears to be stationed at the north pole rather than the equator (which is odd, because the svg uses a rather abstract representation of the globe, without any recognizable continents), and that the SVG does not mention geosychonronous orbit (which just isn't true; it does include that label). I must say I'm rather disappointed at the choice to completely cast this image aside due to some fairly minor qualms. Is there any good reason why it shouldn't be swapped back in? ~ Booya Bazooka 23:14, 24 November 2008 (UTC)


 * I must admit, it does really rather give the impression of orbiting at the North pole. The central continent looks a lot like africa/europe and the bit to the south looks like Australia. Of course it's completely non geographically accurate, but that does seem to be the impression. If you rotate the Earth through 90 degrees or something that might fix it. FWIW in general, I find the use of svg to be rather theoretically better than actually contributing to the project. svg are not significantly more scalable or device independent than gif or anything else for the purposes of the wikipedia, as the latest version of Firefox demonstrates only too well.- (User) Wolfkeeper (Talk) 01:33, 25 November 2008 (UTC)


 * I don't think rotating the planet would help. The current image clearly depicts the pole, while the arrow indicates an equatorial orbit. The SVG might be an abstract depiction of a planet, but it loses the suggestion of a top-down view. I am not opposed to replacing it with an SVG version, as long as the replacement is at least as descriptive as the current image. Wronkiew (talk) 01:49, 25 November 2008 (UTC)
 * I'm the Verdatum of which Booya speaks. My position matches Wronkiew.  I happily would have edited the SVG to add some clarification of the image orientation, but my Inkscape skills are fairly mediocre, and the PNG image still existed and was perfectly acceptable.  I would suggest adding a more accurate representation of the North or South Pole, and/or perhaps add some labels describing the planet's orientation/rotation, etc. and then sure, bring it in. -Verdatum (talk) 03:38, 25 November 2008 (UTC)
 * (Oh yeah, for everyone's info, this issue was originally discussed here.) -Verdatum (talk) 03:46, 25 November 2008 (UTC)
 * MediaWiki turns the SVG into a PNG in the article - the benefit isn't about browser display. Vector graphics are supposed to be easier to edit.  And my main purpose in making it wasn't to change the file format, but to add the text labels. ~ Booya Bazooka 08:45, 27 November 2008 (UTC)
 * In practice though, they're harder to make, because you have to specify rather more information when you generate them. The toolset to manipulate them is also less reliable and advanced right now which doesn't help either.- (User) Wolfkeeper (Talk) 22:41, 30 November 2008 (UTC)

I just did a quick automatic trace of the raster planet and put it into the svg. Since the globe seemed to be the only point of discussion, and it is now nearly identical to the original, I'm putting the new version back in. A better globe image would still be welcome (the 2.5-megabyte trace makes me a little sad), and I like the idea of adding some markings (I hadn't even realized it was the pole, which is why it didn't make it into my adaptation in the first place). I just wish the image hadn't been out of commission for a year when the fix was so simple. ~ Booya Bazooka 08:45, 27 November 2008 (UTC)

I recommend an illustration that shows the correct scale of the position of geosynchronous orbit with the diameter of Earth. The current illustration is not to scale. Mydogtrouble (talk) 18:00, 14 January 2009 (UTC)
 * If I'm not mistaken, for the image to be to scale for a geostationary orbit, the length from the the center of the earth to the center of the Center of mass for the elevator would need to be approximately 6.62 times the length from the center of the earth to the outer edge/equator (42,164km / 6,371.0km). I'm not certain if this would look silly or not.  If anyone is interested, I suppose they can try it out, and if it's not unreasonable, it might not be a bad idea. -Verdatum (talk) 19:33, 14 January 2009 (UTC)

Entire Mass of Cable
Estimating the required mass of the entire cabling system would be very useful here. My calculations show an approximation of roughly 1,000,000 metric tons of material required if the strongest estimates of buckytube are used. I would certainly be grateful if someone (preferably several contributors) checked with their own calculations.Mydogtrouble (talk) 19:38, 30 November 2008 (UTC)


 * It depends on the payload size you're trying to lift. IRC a payload to tether ratio of a few thousand is typical, depending on the CNT strength.- (User) Wolfkeeper (Talk) 22:38, 30 November 2008 (UTC)


 * I'm afraid your calculations (and those of any other editors) are Original Research. The mass of the cable should only expressed in this article as figures that can be attributed to reliable published sources. -Verdatum (talk) 19:51, 14 January 2009 (UTC)

Artificial gravity
In the discussion about what could potentially be the anchor for a space elevator, there is mention of locating a space station at the end. It occurred to me that being above GSO, there would be a substantial centripetal acceleration, and thus simulated gravity without the need for a spinning space station. Is this benefit mentioned in the relevant literature, and if so, does it bare mentioning in the article? ce1984 (talk) 09:48, 30 January 2009 (UTC)

Clarification needed re: Equator
It's not really clear from the article that a tether type space elevator must be constructed at the equator. You can sort of deduce it from some of the wording of the article, and from the concept itself, but it's never actually mentioned directly. I wasn't actually sure, until I looked at the Space fountain article, where it is mentioned in the intro paragraph.--Pariah (talk) 00:29, 19 March 2009 (UTC)

Materials strength -- self-length
There's a concept known as self-length, designating how long a strand of a material can be before it breaks under its own weight. That's something that should be included here, because it makes it clear to laymen what sort of strength is required, and enables simple comparisons to available materials. I have no idea what the self-length of a buckytube cable might be; self-lengths of things such as steel cable, hemp, and nylon cab;e are easily available. Not too many people grasp tensile strength, but this is a concept I've had no trouble explaining even to younger teens.

Dismalscholar (talk) 06:47, 7 January 2009 (UTC)


 * You going to tackle the issues of harmonic oscillation which plague any suspension bridge too? Tethers are structurally similar to suspension bridges. Under harmonic vibrations, self-length support gets shorter and length also effects the frequencies and strength of harmonic vibrations. Simple tethers would vibrate like a guitar string on sudden loading -- not to mention effects on any tether that actually dipped one end into the upper atmosphere. The upper atmosphere is thin but still present even if heating from friction is acceptable. Minor vibrations that shuttle crews feel might be entirely different when applied to scores of kilometers of cable instead of the handful of shuttle meters.


 * How about the other issues of loading shock caused to the structure when loads are attached? Instantaneous loads during initial tethering are far higher than sustained loads especially if the object to be picked up is slightly off from the optimal position for attachment (real life affects of weather or minor booster engine performance etc) by a few 100 meters. All you commonly see are the sustained load calculations. But like for real aircraft it is often the few moments of landing or in this case attachment that cause peak stresses and structural fatigue. Engines have fallen off jetliners due to such things when the aircraft industry was much more mature than the tether building industry. And that usually happened with all theoretical equations showing material strength excessing maximum forces by several factors...as many as 10.


 * I have a feeling that all that is too technical for public consumption or even 3rd party authoritative inspection...despite the fact that collapsed bridges prove that engineers can make mistakes of oversight or miscalculation. The "off the record" answers I have heard from some interested but unfunded physics academics are that is more important to get the first tether built first before publicly addressing that issue or other difficult engineering complications. Basically if initial tests show a big problem these folks are in favor of simply de-rating that first tether's load lifting and call it a proof of feasibility project. Yikes! I hope that first tether is in lunar use then. For truly large cost projects the official funding and also the politics of extreme opposition sure make me uncomfortable with Wikipedia rules on authorities. One political side or the other basically controls those accepted voices Wikipedia will accept while fencing out many well-qualified people because they have no officil project involvement nor media selected role as spokesperson for the fanatic opposition. Basically Wikipedia "original research" rules can easily exclude the voices of qualified and unbiased moderates.


 * But people shouldn't be too concerned. I suspect that the disaster scenarios of opponents are a bit ivory tower as well. I doubt that a broken cable or falling tether assembly would repeatedly whip the face of the earth and squirm all about. One impact and it would shatter or embed itself in the crust. So the area of total destruction is unlikely to be more than a kilometer wide even if up to hundreds Kilometers long or just as likely most the tether will follow itself own length to pile up in one relative small area only a few kilometers across. Unfortunately we are unlikely to get good disaster projections from the same place as we get the official construction and safety info. In high stakes projects like this authorities tend to polarize into pro-construction "its as safe as houses" and "we need not specify complete disaster scenaroes" and the anti-construction side that publishes nothing but horrific and unlikely (even impossible) disaster calculations. 69.23.124.142 (talk) 19:37, 8 June 2009 (UTC)

Rotating Space Elevator concept
from PhysOrg.com, May 21, 2009: Rotating Space Elevator Propels its Own Load "The idea of the space elevator just got a little crazier. While the “traditional” concept involved using rocket propulsion or laser light pressure to propel loads up a cable anchored to Earth, a new study shows that a rotating space elevator could do away with engines or laser light pressure application completely. Instead, the unique double rotating motion of looped strings could provide a mechanism for objects to slide up the elevator cable into outer space. The space elevator could launch satellites and spacecraft with humans, and even be used to host space stations and research posts." Seems interesting and something that should probably be reflected in the article. N2e (talk) 13:21, 25 May 2009 (UTC)

The Center of Mass is not at GEO
The first image makes you believe that the center of mass is at GEO which is not the case at all http://gassend.net/spaceelevator/center-of-mass/index.html —Preceding unsigned comment added by 82.225.161.243 (talk) 12:18, 6 January 2009 (UTC)

Good point. I think the idea is that the initial orbital construction station needs to be there, and from there people assume that will stay put. Of course that might well be the case, but the center of mass will not at the end be at that station, then. Dismalscholar (talk) 06:49, 7 January 2009 (UTC)

The first image doesn't only "make you believe" this, it actually states it. If this were true, then there would be no tension at the bottom of the elevator. The image needs to be edited (I've posted a message at the image's talk page). -- Dan Griscom (talk) 21:27, 23 June 2009 (UTC)

Distracting Animated Images
The current image of the rotating carbon nanotube is a serious distraction for someone trying to read the text. The eye will naturally turn toward movement and trying to resist this imposes mental stress on the reader. If someone has an image to replace the animated carbon nanotube, I would suggest using it, instead of the current one. Bruhsam (talk) 12:58, 28 January 2009 (UTC)


 * I agree Cmiych (talk) 16:57, 12 June 2009 (UTC)

Only if you have a source, and it benefits the article, of course.--72.74.112.203 (talk) 22:32, 6 May 2009 (UTC)

Space elevators on Mars or the Earth's Moon
If a space elevator on Mars can be much shorter than an Earth elevator, due to lower gravity, why would an elevator on the Earth's moon be very much longer. The Moon has even lower gravity, so the elevator should be even shorter than a Martian one. This discrepancy should be explained.JohnC (talk) 20:03, 25 August 2009 (UTC)


 * It's because the moon only spins once a month, whereas Mars spins every 26 hours or so.- (User) Wolfkeeper (Talk) 20:24, 25 August 2009 (UTC)

Looks like we are going to have an edit war. An anonymous contributor keeps adding a statement of his opinion that a Lunar Space Elevator is unrealistic. The Moon's geosynchronous orbit may be about the same distance as the Earth but that is only a cost issue. The Moon's rotation is tidal locked to the Earth so any space elevator built on the far side will not hit the Earth. Also as the section on Extraterrestrial elevators says the Lunar elevator will probably use one of the Lagrangian points, making it shorter. Andrew Swallow (talk) 04:53, 3 November 2009 (UTC)


 * Nah, he's got no references. He's wrong anyway of course: lunar space elevator.- (User) Wolfkeeper (Talk) 05:57, 3 November 2009 (UTC)

For missing citation in introduction
Pugno M, 2007, The role of defects in the design of space elevator cable: From nanotube to megatube, in Acta Materialia 55 (Elsevier) pp. 5269-5279 gives required strength to weight ratios of space elevator cable, theoretical s:w of carbon nanotube exceeding this, and actual s:w ratio of this material in laboratory tests /still/ exceeding requirements, even allowing for weakness due to the natural rate of defects in manufacture of carbon nantotube. —Preceding unsigned comment added by 129.96.121.117 (talk) 10:16, 10 September 2009 (UTC)

Usefulness of a Space Elevator?
This article really needs a section on just how useful a space elevator would be. What problems are we currently facing that a space elevator would solve? In what ways are the superior to conventional earth-space travel? How useful do world governments and major aerospace organizations see an elevator as being? Gaiacarra (talk) 21:38, 4 February 2010 (UTC)


 * "What good is a new born baby?" (Ben Franklin). Solving current problems is never a good measure of the value of a new idea.  It's a start, but value is not so cut and dried.  It is the new capabilities, often unforeseeable, that give value.  But mostly, it's the JOY of doing something so new and exciting!  :-)


 * 108.7.8.213 (talk) 19:53, 14 March 2010 (UTC)


 * Is anybody in this group interested in reviewing a pair of October 2009 presentations at the International Astronautics Congress that provides an update on the capabilities of using Colossal Carbon Tubes in a "sling" elevator system (modified HASTOL) and in showing how the payload capability could allow control of global warming and replacement of fossil fuels for most applications within a century. Since I am an author of the papers, I cannot contribute information on this material to the article.Aqm2241 (talk) 15:22, 9 March 2010 (UTC)


 * That would probably be to do with Space Tether not space elevator.- Wolfkeeper  15:27, 9 March 2010 (UTC)
 * Do you have a link to a preview or current copy of the article by any chance?- Wolfkeeper  15:27, 9 March 2010 (UTC)

Unclear
"A newly discovered type of carbon nanotube called the colossal carbon tube may be strong and light enough to support a space elevator. Its tensile strength is only 6.9 GPa, but its density is only .116 g/cm3, making its specific strength sufficient for a space elevator. In addition, it has been fabricated in lengths on the scale of centimeters, a headstart on the thousands of kilometers needed for a space elevator.[38]" —Preceding unsigned comment added by Cmiych (talk • contribs) 16:58, 12 June 2009 (UTC)

In general, the entire article seems unclear and confusing, at least in terms of explaining the technical feasability or lack of such. The language is messy, people have edited the article without reading it properly themselves, and it has citation needititis. The entire Cable section is mostly suitable for confusion, especially if the reader has troubled himself with reading other sections, which seems to contradict the parts that are not themselves self-contradictory. In the section Powering climbers, there is an additionally confusing sentence that I cannot make sense of: "The fuel cell used also for the electric vehicle is expected to be used to the climbers of each ton." --anon 84.215.1.3 (talk) 23:59, 4 January 2010 (UTC)

Certainly, various people's sentences mix, and it doesn't understand well. In the section Powering climbers, The fuel cell that I had written was edited. Azure777 (talk) 12:20, 5 January 2010 (UTC)

Math
There's a nice page that does some quantitative calculations. It would be great if his math could be checked and some information included in this article, which in its current form is pretty lite on science. —Preceding unsigned comment added by 24.16.88.14 (talk) 04:54, 18 August 2009 (UTC)

How would you protect something that fragile from terrorists? —Preceding unsigned comment added by 86.2.71.38 (talk) 16:39, 13 January 2010 (UTC)

Dynamics of tethered satellite motion and control
The article seems to be missing a section on the dynamics of tethered satellites such as this would be. The equations of motion of a tethered satellite are considered to be non-linear differential equations with tendencies towards chaotic behavior. Theoretical analysis suggests that this can be controlled by varying the tension of the tether although the scale of the space elevator may require a different approach (http://www.springerlink.com/content/g7327314v627wm84/fulltext.pdf) and others. It doesn't seem consistent with the idea presented in the article that the tether would just point straight upwards and naturally return to that position.

An object moving up or down the space elevator would not change angular velocity as a simple consequence of is height change as the article seems to suggest. It would need to accelerated or decelerated with additional challenges for the dynamics of the system. (QuietJohn (talk) 02:22, 10 January 2010 (UTC))
 * But it would change angular momentum, and that's where problems arise.96.54.53.165 (talk) 01:40, 13 January 2010 (UTC)


 * The climbers do not go up at exactly 90° but are about 1° off the vertical. That is sufficient to give them the required additional angular velocity, we are talking a distance of 22,300 miles.  Andrew Swallow (talk) 06:21, 14 January 2010 (UTC)

The orbit of the counterweight will become unstable, if the force of the cable is not 90°. 91.65.128.78 (talk) 07:23, 22 April 2010 (UTC)

I saw (skimmed) a few papers out there (Edwards and others, I'll look for them again) that showed the primary oscillation mode to be the one we are all concerned about, the one that is almost entirely undamped, the first mode (zeroth?), the one that is like an upside down pendulum, having a period of about 8 hours. All other modes have good enough natural damping. For example, the first guitar string-like mode has damping because it transfers energy into stretching, which dissipates as heat. All harmonics of the guitar string modes do this. The upside-down pendulum mode is activated (east and west) by climbers moving up and down, but it can be actively damped by the same. North-south pendulum movement (as well as east-west) will be dampable by moving the anchor around in the right phasing. Although, I don't know how much energy can be extracted out with a given amount of "movin' the anchor around". There are other methods of damping the main mode too.

The papers I saw gave a maximum (or typical?, don't remember) deflection of the counter weight (CW) from vertical of about 1/2 degree. That's still very very vertical, though given the length, even large-ish CW deflections make for very small angular deflections. That 1/2 degree deflection equals hundreds of miles at the CW. Max deflection of the main oscillation equates to energy stored in the oscillation and the energy equating to large angular deflections was computed to be some sort of crazy-huge amount (meaning unlikely). Nobody would build a design if the oscillation and damping was not thoroughly considered, but it looks like it won't be an insurmountable problem.

108.7.8.186 (talk) 23:54, 10 June 2010 (UTC)

Does M5 Fiber help the case any?
I read that M5 has a theoretically attainable strength of 8.5 to 9.5 Gpa, is less brittle than carbon fiber, is UV resistant, more fireproof than Nomex, and twice as damage-resistant as Kevlar under ballistic conditions. I don't know enough about M5 to estimate its specific strength / gravity.


 * Nah. You need a minimum of about 45 GPa to stand any chance.- Wolfkeeper  06:16, 11 February 2010 (UTC)

"GPa" as a measure of required breaking stress assumes a density - the density of carbon nanotubes. CNT's need to have at least 45 GPa breaking stress (given their density). But, the figure varies for other materials depending on their density compared to CNTs. If the other material's density is one half CNTs, the required breaking stress would be 22.5 GPa (half of 45). So, the density of those other materials must be considered. To meet the 45 GPa (at CNT density) given by Wolfkeeper, the materials would need to also be about 9/45 (20%) the density of CNTs. They may or may not be lower in density than CNT, but they are not likely to be as low as 20% of the CNT density. So Wolfkeeper is right, but for incomplete reasons.

108.7.10.185 (talk) 02:52, 1 September 2010 (UTC)

"Cable material" section is flakey, mostly off topic.
The section seems to assume density to be the same for all materials, then goes further to suggest that the required free breaking length for a planet is roughly the same as its radius. Those two estimates, both wild imho, may be roughly true, but to justify them would require way more explanation and would be even more off topic.

I didn't delete the section because it mentions free breaking length, which is an important material property for SE cable materials. Still, the other stuff needs to go.

108.7.163.81 (talk) 00:33, 24 August 2010 (UTC)
 * I saw your edits. Looks good to me. Go ahead and be WP:BOLD  SPLETTE &#32;:]&#32;How's my driving? 00:38, 24 August 2010 (UTC)


 * Certainly, the cable material is the most important part of the article. (Whilst plenty of publicity goes into the like of crawlers, the material technology is the greatest physical impediment to even contemplating a time scale for getting the project off the ground.) How does Graphene ribbon compare? Cesiumfrog (talk) 11:59, 17 November 2010 (UTC)

Why ride all the way up?
With the time estimates given (e.g. 85 days) the article suggests that the elevator needs to ride all the way up the cable. But if the elevator is sent up with 1/2 the supportable weight, then once it's out of the atmosphere it can simply apply the force needed to support twice its mass. This 2g acceleration would support its weight with a 1g acceleration left over. Within minutes the elevator would reach escape velocity and could simply detach from the cable. Wnt (talk) 23:22, 27 August 2010 (UTC)


 * I'm not sure I know what you are trying to say, but I'll try. "Simply apply the force..." is not so simple for one thing.  Getting power to the climber at all is a technical challenge, let alone the power for such constant acceleration.  Also, most of the energy a vehicle has at GEO on a SE came from slogging the climber against gravity over that long long distance, BUT about 10% (if i recall) comes from the cable providing horizontal speed by way of Coriolis forces.  As the cable pushes eastward on the climber to give it the horizontal speed, the climber pushes BACK (westward) on the cable.  The faster the climber goes up, the harder it pushes westward on the cable.  You can imagine the bending and flopping and breaking the climber can do at your proposed speeds.


 * That's not to say a significant improvement in speed won't happen as the systems mature over the decades.


 * I corrected that 85-day figure in the article. It was for really really early "garage-built" prototypes that are unrelated to an operational system. An operational system would design an ascent speed according to profitability (or other) requirements.  I think (if I recall) the transit times I saw for early systems were about 5 days (not 85 days).  A 5 day transit has an average speed of 186 mph, which is on the order of the things I've read.  However, maybe the construction climbers will go slower as they build up the cable during their climbs.


 * Skyway (talk) 03:32, 1 September 2010 (UTC)

WikiProject Space
This article needs to be brought under the umbrella of Wikipedia talk:WikiProject Space. Tom Haws (talk) 15:30, 2 November 2010 (UTC)
 * The article has already been tagged with the WikiProject Space banner.. maybe you had something more in mind? Mlm42 (talk) 21:13, 6 November 2010 (UTC)

Spindle extraction system
Why use a permanent system of transportation? Apply the mechanics of a reel on a fishing rod, on a bigger scale, and combine that with whatever cable would be used or invented for almost any other space elevator and use these simple too;s to extract things from Earth. The Basic principles of a stationary elevator without the commitment, or dangers of being stationary, are applied, the only change is in the propulsion. —Preceding unsigned comment added by JDMONTY (talk • contribs) 23:18, 25 September 2010 (UTC)
 * Find us some documentation or reliable sources on that. Wikipedia generally doesn't use original research and theories. Pär Larsson (talk) 11:57, 10 March 2011 (UTC)

Problems with the main (first) diagram.
The main picture/diagram has a few flaws:

1) The scale isn't right. It is easy to get the ratio between the GEO level height above the surface and the Earth radius correct.  That ratio is about 5.62 by the way.  It should be a simple matter to make the Earth a little smaller.

2) The center of mass of the system at all times must be at least somewhat above the GEO level. The diagram shows the center of mass to be at GEO level.  The arrow pointing to GEO needs to be scooted up a bit.

3) Modern (post Edwards-Westling) concepts don't use an asteroid as a counterweight. The diagram shows something that looks like an asteroid.

If no one makes the fixes in the next week or so, I will have a go at it. It is pretty important I think. The association of space elevators with GEO isn't as significant as most think. We tend to frequently invoke the idea of "dropping a massless line from a satellite at GEO" to explain, but that misleads people to give undue significance to GEO in the idea of space elevators. It also leaves the idea of "pulling a space elevator down" nagging in the minds of novices, as if that really could happen in a properly managed system. It would happen immediately however, in the system illustrated in that diagram. The CM being above GEO, even when under load, and providing a margin of "excess tension" is an essential element of the concept. That's why it should be correctly illustrated in that diagram.

Skyway (talk) 06:58, 1 April 2011 (UTC)

I couldn't wait a few days. I went ahead and made the above changes along with the relabeling of "Geosynchronous orbit" to "Geostationary orbit" as was also suggested. I still need to correct an error I made with regard to the Name header. I had incorporated it into the picture then saw that it was a part of the infobox and taking up space even if I nulled it out. I will edit the diagram to remove the name, then restore the Name as part of the infobox as it was before.

Skyway (talk) 09:37, 2 April 2011 (UTC)