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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)
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)
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 The article was changed to reflect the later date but has been changed back to the out of date value.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: [1]
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)
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)
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)
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)
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)
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)
(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.
(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)
"[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)
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)
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)
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)
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)
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)
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
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)
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)
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)
Space elevators don't exist, therefore nothing happens when they have an (imaginary) shift change! Yobmod ( talk) 17:56, 11 August 2008 (UTC)
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)
" 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 — citation needed 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. citation needed
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. citation needed 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. citation needed"
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)
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 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)
The links to http://www.isr.us/Downloads/niac_pdf/ chapters are dead but they were available on the Internet Archive. This appears to be self-published, hence is not a reliable source. 59.167.37.230 ( talk) 13:30, 24 September 2008 (UTC)
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)
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.
Mech Aaron ( talk) 19:18, 29 September 2008 (UTC)
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.
Comments? Cosmomancer ( talk) 08:33, 27 September 2008 (UTC)
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 chitchat seemywork 02:26, 28 September 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 citation needed 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:2008Olympian chitchat seemywork 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)
I have requested temporary semi-protection from the anon IP vandalism. Cosmomancer ( talk) 06:18, 11 October 2008 (UTC)
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)
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 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)
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)
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)
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)
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)
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. [4]
Seems interesting and something that should probably be reflected in the article. N2e ( talk) 13:21, 25 May 2009 (UTC)
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)
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)
Only if you have a source, and it benefits the article, of course.-- 72.74.112.203 ( talk) 22:32, 6 May 2009 (UTC)
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)
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)
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)
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)
"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)
There's a nice page that does some quantitative calculations [5]. 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)
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))
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)
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.
"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)
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)
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)
This article needs to be brought under the umbrella of Wikipedia talk:WikiProject Space. Tom Haws ( talk) 15:30, 2 November 2010 (UTC)
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)
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.
This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 | ← | Archive 5 | Archive 6 | Archive 7 | Archive 8 | Archive 9 | Archive 10 |
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)
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)
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: [1]
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)
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)
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)
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)
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)
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)
(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.
(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)
"[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)
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)
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)
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)
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)
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)
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
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)
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)
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)
Space elevators don't exist, therefore nothing happens when they have an (imaginary) shift change! Yobmod ( talk) 17:56, 11 August 2008 (UTC)
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)
" 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 — citation needed 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. citation needed
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. citation needed 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. citation needed"
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)
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 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)
The links to http://www.isr.us/Downloads/niac_pdf/ chapters are dead but they were available on the Internet Archive. This appears to be self-published, hence is not a reliable source. 59.167.37.230 ( talk) 13:30, 24 September 2008 (UTC)
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)
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.
Mech Aaron ( talk) 19:18, 29 September 2008 (UTC)
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.
Comments? Cosmomancer ( talk) 08:33, 27 September 2008 (UTC)
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 chitchat seemywork 02:26, 28 September 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 citation needed 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:2008Olympian chitchat seemywork 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)
I have requested temporary semi-protection from the anon IP vandalism. Cosmomancer ( talk) 06:18, 11 October 2008 (UTC)
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)
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 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)
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)
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)
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)
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)
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. [4]
Seems interesting and something that should probably be reflected in the article. N2e ( talk) 13:21, 25 May 2009 (UTC)
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)
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)
Only if you have a source, and it benefits the article, of course.-- 72.74.112.203 ( talk) 22:32, 6 May 2009 (UTC)
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)
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)
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)
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)
"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)
There's a nice page that does some quantitative calculations [5]. 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)
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))
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)
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.
"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)
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)
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)
This article needs to be brought under the umbrella of Wikipedia talk:WikiProject Space. Tom Haws ( talk) 15:30, 2 November 2010 (UTC)
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)
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.