Talk:Space elevator/Archive 6

message: Ok, so I did a whole bunch of googles to find out what terms are most popular:
*Results 1 - 10 of about 1,960,000 for beanstalk [definition]. (0.23 seconds)
*Results 1 - 10 of about 482,000 for "space elevator". (0.26 seconds)
*Results 1 - 10 of about 318,000 for beanstalk space. (0.28 seconds) 
*Results 1 - 10 of about 49,900 for beanstalk elevator. (0.21 seconds) 
*Results 1 - 10 of about 35,900 for "space bridge". (0.18 seconds) 
*Results 1 - 10 of about 27,500 for "space elevator" tether. (0.17 seconds) 
*Results 1 - 10 of about 1,210 for "star ladder". (0.07 seconds) 
*Results 1 - 10 of about 743 for "geosynchronous orbital tether". (0.40 seconds) 
*Results 1 - 10 of about 732 for beanstalk "space elevator". (0.42 seconds) 
*Results 1 - 10 of about 594 for "space bridge" "space elevator". (0.39 seconds) 
*Results 1 - 10 of about 560 for "orbital tether". (0.48 seconds) 
*Results 1 - 10 of about 494 for "star ladder" space. (0.69 seconds) 
*Results 1 - 10 of about 370 for "space bridge" beanstalk. (0.28 seconds) 
*Results 1 - 10 of about 272 for "space ladders". (0.26 seconds)
*Results 1 - 10 of about 854 for "space lifts". (0.21 seconds) 
*Results 1 - 10 of about 151 for "star ladder" elevator. (0.26 seconds) 
*Results 1 - 10 of about 134 for "star ladder" space elevator. (0.64 seconds) 
*Results 1 - 10 of about 67 for "space lifts" "space elevator". (0.25 seconds) 
*Results 1 - 10 of about 49 for "space ladders" "space elevator". (0.36 seconds) 
*Results 1 - 10 of about 13 for "star bridge" "space elevator". (0.30 seconds) 
*Results 1 - 1 of about 7 for "space lifts" beanstalk. (0.19 seconds) 
(Note these will vary over time as pages come and go and as google changes their page rank and so Results 1 - 10 of about 65 for "space ladder" geosynchronous. (0.28 seconds) forth.)
Analysis:
Beanstalk is the most popular, but only because of 'Jack and the Beanstalk'. Clearly 'beanstalk' on its own isn't enough; because beanstalk is ambiguous. If you remove that the correct order seems to me to be: space elevator, beanstalk, space bridge, space lifts, star ladder
WolfKeeper 21:23, 14 January 2006 (UTC)
replies: text: Actually, "orbital tether" seems to be the second most popular term, ahead of 'beanstalk'; but it's not clear that it means the same thing as beanstalk- an orbital tether can be a bolus or a rotovator or whatever. Incidentally, I get very slightly different results, I'm using google.co.uk; that might have something to do with it.WolfKeeper 23:23, 14 January 2006 (UTC)

text: I tried "geosynchronous orbital tether" but although google initially looked incredibly promising, the only hits I found on this were actually the wikipedia mentions of it!!! (Try it and see- click to the end of the matches!)WolfKeeper 23:32, 14 January 2006 (UTC)
replies: text: Hrmph. Which means that in accordance with our manual of style preference for the "most common title", the orbital tether variant of space elevator should be under the title "space elevator". Leaving no obvious place to put the stuff from the beginning of the article overviewing the whole concept of running elevator cars up a generic really tall structure. Since "space lift" appears to be not very common at all, perhaps I could hijack that title for this purpose? Bryan 01:36, 16 January 2006 (UTC)
thread_title: Naming Issues

message: There is a section that recognizes sabotage as an area of consideration when planning a Space Elevator, as well as ways to protect against it. But what ARE these anti-terrorism plans? Gigem12 06:32, 1 July 2006 (UTC)
thread_title:  Sabotage 

message: Is there a space in the non-tether solutions for Lofstrom's idea to be mentioned?  I rather like it.Midgley 18:59, 16 March 2006 (UTC)
replies: text: I think the Space fountain article would be a better place for that, since it's closely related to the space fountain concept, but currently only minimally mentioned in that article. KarlBunker 19:12, 16 March 2006 (UTC)
thread_title:  Lofstrom Loop 

message: I was just wondering, how far one could see the elevator if such a thing would be constructed? —Preceding unsigned comment added by 212.149.214.123 (talk • contribs) 
Depends on a number of factors, really.  Time of day, how refractory the outer layer of the ribbon is, the ultimate dimensions, weather, angle of view, etc.
We think the ribbon - on the first generation SE - is going to be a meter wide (average) and paper thin.  Depending on your angle you'll have a hard time seeing just the ribbon more than a kilometer away under optimal conditions. Bdunbar 21:30, 24 March 2006 (UTC)
replies: text: But of course, there would be at least one time of day when the sun is just right and you'd be able to see the ribbon for hundreds of miles. Val42 17:57, 25 March 2006 (UTC)
replies: text: I think it would oscillate and twist enough that there would be no one unique time and direction.  Only a very small proportion of the ribbon is going to be within hundreds of miles of anything from which it might be seen - except the climbers... Midgley 16:09, 26 March 2006 (UTC)
replies: text: It just occurred to me that from the right viewpoint, the ribbon would catch the light after the sun has set, so it would be lit up against a dark sky. That might make it visible for a huge distance--depending on this, that, and the other thing, of course. KarlBunker 16:16, 26 March 2006 (UTC)
thread_title:  Visibility 

message: At time of writing, the article used 5.294e10 m^2/s^2 as the factor in the taper ratio calculation. However, substituting values in to the equation () seems to give a value of 4.832e7 m^2/s^2.
Also, in (J. Pearson, "The orbital tower: a spacecraft launcher using the Earth's rotational energy" in "Acta Astronautica" vol 2 pp. 788, 1975) Pearson uses the equation:
{A \over A_{0}} = \exp \left[{0.776r_{0} \over h}\right]
where h = {s \over g_{0}\rho}. Substituting h into the equation gives:
{A \over A_{0}} = \exp \left[{\rho \over s}{0.776r_{0}g_{0}}\right] and  gives 4.840e7 m^2/s^2, which agrees with the figure of 4.832 given above (the difference is because the factor of 0.776 is rounded). I shall change it myself and reference Pearson's paper, but I'm placing justification here for future reference. Someone42 12:10, 18 April 2006 (UTC)
thread_title:  Taper calculation wrong 

message: Um, what exactly is "magnetospheric braking of the cable to dampen oscillations"?
--Simonf 05:21, 17 May 2006 (UTC)
thread_title:  magnetospheric braking? 

message: I removed this from the article:
:There are two approaches to having a stable system:  	 
: 	# either the counterweight must be positioned to the west of the tether point on the Earth, and matter must be raised up to orbit at a constant rate for the whole lifetime of the space elevator, so that the cable hangs vertically from the counterweight (see diagram), and all the angular acceleration comes from the Earth 	 
: 	# or the angular momentum of the matter brought down from orbit to the Earth's surface must be exactly equal to the angular momentum of matter taken up into orbit at all times. 	 
: 	If neither of these approaches is followed, the orbital velocity of the counterweight will change with time, which leads to complex (and often unpredictable) motion of the counterweight around the tether point on the Earth. The second approach is the one which is most commonly suggested, usually using mass from the counterweight to compensate for matter lifted into geostationary orbit. Note that a temporary shift of the position of the counterweight just during the lifting process is not feasible, as all approaches which deliver a stable shift to the position of the counterweight during the lift of an object (changing the orbital phase of the counterweight, but keeping the orbit circular, and then changing it back) would require more rocket thrust applied to the counterweight than would be required for a conventional rocket launch of that object from Earth.
::This is just wrong. As the payloads climb the counterweight moves around, but no propellant burn is ever needed. There are some issues due to lack of damping, but timing the payloads can damp out any oscillations that may build up.WolfKeeper 12:31, 12 June 2006 (UTC)
replies: text: The elevator is like a swing hanging off the Earth. If you send a single payload up, you start it swinging; but if you time the next payload correctly the swing cancels out (the elevator has a natural resonance of about 10 hours I believe; so sending another payload up at the 5 hour mark cancels the swing from the first. Sending payloads more frequently than that damps it out even more. You have to control climb speeds and so forth- the coriolis force is proportional to climb speed, careful control of speeds can damp the cable out entirely.WolfKeeper 12:31, 12 June 2006 (UTC)
thread_title: Angular momentum, speed and cable lean

message: "A lunar space elevator would need to be very long—more than twice the length of an Earth elevator, but due to the microgravity of the moon, can be made of existing engineering materials." -- The word was linked to the Microgravity article. If anyone had read it, they would have known that it was the wrong word to use here. Ravenswood 18:30, 23 June 2006 (UTC)
thread_title:  Microgravity 

message: According to The Guardian , NASA will be inviting bids to build a space elevator, during this month (September 2006). If this is true, this is exciting news, however I didn't realise current technology is ready yet. The Guardian didn't state its sources for this report.
:It is just a contest on some of the basic technologies, small-scale climbers, short sections of cables and so on.  No, the technology is not ready for a full scale project. --DevaSatyam 16:38, 3 September 2006 (UTC)
thread_title:  Nasa opening bids to build? 

message: This really isn't a current event.  We may expect significant updates maybe every few months.  But this doesn't make it necessary to view it as a current event surely?  Barnaby dawson 21:14, 3 September 2006 (UTC)
thread_title: Current event

message: The cable thickness equation is summarized as follows:
This equation gives a shape where the cable thickness initially increases rapidly in an exponential fashion, but slows at an altitude a few times the earth's radius, and then gradually becomes parallel when it finally reaches maximum thickness at geostationary orbit.
As a casual reader (me), the word "parallel" makes no sense.  How can the cable thickness go from "increasing rapidly" to "slows" and then to "parallel?"  Parallel to what?  Please adjust.  JM 216.165.146.161 07:28, 28 September 2006 (UTC)
thread_title:  Equation summary/description 

message: Am I the only who thinks this article is far to long? When it gets to the point that editing gets slow it is well beyond what it ought to be.
Nobody sits down and reads through all this. I would recommend that some sections were moved into their own articles and that there was a much shorter section about them here(as hs happened with Space elevator economics). Elentirmo 00:26, 14 December 2006 (UTC)
replies: text: I think the Space elevator economics example is a bad one, since that article is both disputed and in need of cleanup.  However, I agree that this article is a bit long and excessive at points.  It might be better to try and cut out some of the less important information and tighten up the text before starting new articles about sub-topics within this article. Grant 19:29, 3 January 2007 (UTC)
replies: text: The space elevator economics article came into existence after one editor who had a very strong POV on whether space elevators were practical added large amounts of detail to the article in support of it and other editors started adding "counter-arguments" neutralizing it. It's not surprising that the end result still bears the scars of that dispute. :) I suspect splitting stuff out purely because of size concerns would have a cleaner result. Bryan 20:37, 21 January 2007 (UTC)
thread_title: Too Long!

message: Reference #16 says it's a 404 error at the location it was originally found.  However I found it here, should I update the link even though it's not on a NASA website?  Grant 19:18, 3 January 2007 (UTC)
replies: text: If it's the same source document I don't see any reason why not. A book is the same book no matter which library it's found in. Bryan 20:38, 21 January 2007 (UTC)
thread_title:  References 

message: I wandered away from this article for a while to do other things but I think a major problem I raised in #About this word 'Plausible' is still unresolved. The intro paragraphs for this article talk about how all sorts of structures that reach from ground to space fall under the classification "space elevator", and then there's an "orbital tether" header and everything after that reads like a separate article on just orbital tethers. Basically, there are two separate articles on two different topics that are spliced together in one page. My proposal before was to split off the orbital tether section into its own article (orbital tether), leaving space elevator as a general overview of the various concepts, and although objections was raised they were very nonspecific as to what was wrong with the idea. Does anyone have any other solutions to suggest, or specific details as to why my proposed solution is bad? Bryan 20:13, 14 January 2006 (UTC)
replies: text: Well, we shouldn't decide what these things should be called - that'd be original research. All I'm proposing here is that this article should be split because it's two articles smooshed together, what we ultimately call these things is ambiguous and we'll need all sorts of "also known as"es in the opening line. Bryan 22:37, 14 January 2006 (UTC)
replies: text: Shouldn't the history part head the article ? --Anne97432 06:59, 27 April 2007 (UTC)

text: The terms "bean stalk" and "space elevator" are generally used interchangeably in the engineering literature to refer to an anchored cable or tower extending from Earth/ground to Geosynchronous Earth Orbit and a bit beyond with the counterweight.   "Fountain" is a special elevator, the structure rides a high speed momentum exchange medium (typically iron/steel loops) rather than supporting itself.  An orbital/space tether (also a standard term easily citable in the engineering literature) is a completely different animal from an engineering and operations standpoint.   Merging/leaving these two in the same article makes about as much sense as putting sea ferries in with bridges.  The key difference is that one rides/climbs the elevator/beanstalk/tower like an elevator.  The space tether (skyhook) tosses the cargo on vector planned. In my opinion Wikipedia would be better off with a couple of appropriate stubs or half articles ... assuming they could avoid deletion while they were improved.  Anybody interested could start a discussion of engineering details or approaches at www.wikiversity.org   Perhaps a decent summary of various engineering approaches would eventually result that could be transwikiied/merge back to Wikipedia.  Lazyquasar 02:01, 25 September 2007 (UTC)
thread_title:  Article organization still has a big structural problem 

message: How can the slowing of the earth caused by the existence of the lift only 'insignigicantly slow' the Earth's rotation? Surely any slowing of it's rotation is a very bad thing and would need some form of countermeasure? The fact that this topic was skimmed over in the wiki gave me cause for concern.
129.11.76.215 09:04, 1 March 2007 (UTC)
replies: text: The same way that whenever you walk towards the west the earth is insignificantly slowed (and insignificantly sped up when you walk to the east). The great disparity of mass of the earth versus your body (or indeed a space elevator and payload) means that the actual slowing experienced is so infinitesimal as to not warrant worry, but does deserve a breif entry into the physics section of the Space Elevator wiki. Also, presumably an operational space elevator would have mass coming down as well as going up, so there's your countermeasure. ABVS 01:58, 3 March 2007 (UTC)
replies: text: Or it may be the other way around - east slows, west speeds up... sun rises in east.. earth rotates to east... yes I think I was wrong the first time.ABVS 01:10, 4 March 2007 (UTC)

text: The angular momentum of the Earth is: 7.06 x 10^33kg m^2/s. The angular momentum of an object weighing 1000 kg (1 tonne) in Geosynchronous orbit is 42,164,000m * 3071 m/s * 1000 = 1.296^14 km m^2/s. So to add 1 second to a year we would have to decrease the angular momentum of the Earth by a fraction of 1/(365.25*24*3600) = 1/31557600. Multiply that by the angular momentum of the Earth and divide by the angular momentum of the object and we get 1.726 e 12. In other words you would have to launch a million, million tonnes into Geosynchronous orbit to slow the rotation rate by 1 second per year (if I haven't messed up my arithmetic.) But even if we did that, the normal variation of the rotation of the earth is about 1 second a year anyway (see leap second), due to weather and other effects, so nothing bad would happen(!) Hope this helps.WolfKeeper 03:23, 3 March 2007 (UTC)
thread_title:  Insignificant Slowing of the Earth 

message: Like the title says, I'm wondering if there is any information on the hanging tether idea. It's basically the same idea as the normal elevator, but is only 4K long (with COM at 2km), and the Earth end of the cable has a sky-hook/platform for rockets to transfer cargo to the elevator. I understand that it's being developed for the next X-prize, but I only have Japanese language sources on it so I don't want to add it to the article. Anyone know anything about it? -- Bakarocket 17:01, 6 March 2007 (UTC)
replies: text: The idea was discussed extensively by Robert Zubrin in an article in Islands in the Sky: Bold New Ideas for Colonizing Space ().  I don't know anything about it being part of the next X-prize, though. siafu 17:57, 6 March 2007 (UTC)
replies: text: Should it be added into the article as an alternate version in 4.3, or is there another article already available? For the X-Prize part, I just did an interview on a guy involved with the project, which is why I came here looking for some back-up. It would be intellectually dishonest for me to use my own print article as a source though, which is why I was looking for other English sources. I've never touched this article, so I thought I'd ask the regulars first. -- Bakarocket 18:30, 6 March 2007 (UTC)
replies: text: Where is your article published? siafu 16:43, 10 March 2007 (UTC)
replies: text: It won't be out until next month, and it'll be in an English newspaper in Japan. I'm not going to add anything until I can source it from Zubrin's piece, though. I'd feel dirty.-- Bakarocket 05:04, 11 March 2007 (UTC)
thread_title: Any English info on the hanging tether idea?

message: I'm intrigued by the idea of a space elevator. But surely there are similar applications that would cost far less to implement and should be mentioned in this article. Off the cusp, I can imagine a space pump for ridding the world of gaseous, solid, and nuclear waste. We could pipe all our waste to a network of regional pipes that could then be ejected through a central space pump into outer space. Obviously, the harmful waste would have to be ejected with a sun-bound trajectory so it would be incinerated. Bet that would put a significant dent in our polution and waste problems. Moto 02:31, 10 March 2007 (UTC)
replies: text: SOrry, what? Are you suggesting a new form of transport?--Bakarocket 12:00, 10 March 2007 (UTC)

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

message: Partly as a matter of interest and partly because maybe it should be added to the page, does anybody know how elongation and deformation from tension (and maybe even tidal forces) would affect the calculations? —The preceding unsigned comment was added by 207.112.60.14 (talk) 00:01, 29 March 2007 (UTC)
replies: text: Given that the loading is purely axial, the poisson ratio is not so important as the cable taper can easily be designed to account for the stretching effects.  According to our article on carbon nanotubes, the elastic modulus of the material is on the order of 1 TPa; just back-of-the-envelope assuming a length of 42,164 km (GEO), an average thickness of two meters (a convenient cross-sectional area of pi meters), and a loading at the "end" of ~70 MN (this one is just a guess), the total elongation would be about 940 m.  This is about 0.0022% the entire length of the cable (i.e. the strain is 22E-6).  This would affect the caculations only very slightly, but would be more important in calculating the oscillating behavior of the structure, which is much, much, more complicated. siafu 01:00, 29 March 2007 (UTC)

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

message: Anyone? —The preceding unsigned comment was added by 24.168.30.85 (talk) 01:25, 29 March 2007 (UTC)
replies: text: No. siafu 01:45, 29 March 2007 (UTC)
thread_title:  Wouldn't The Counterweight change the earth's orbit and kill everyone 

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

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

message: I am aware of No Original Research, though I reckon that it must be the case that someone has already published what I am stating here, and hence that the information is citable.  But, would strategically placing Helium Balloons at certain points along the tether aid the feasibility of creating the elevator?  I believe that this might be so as the tension along certain points of the tether would be reduced via the use of such balloons (they would relieve the tension of the tether from under it's own weight at several strategic points along the tether).  However, this is only something that could be done up to a height of about 20 miles up (the height to which most helium balloons will go.  You might be able to squeeze out some more height using Hydrogen.  It may even be possible to create several mile high rigid `floating structures' attached to helium/hydrogen balloons that could support the tether 30 miles up or so by attaching so structures to such balloons.  Nevertheless, I remain pessimistic that the (600 mile?) barrier for fully fledged space access is traversible from such meagre heights (though, in actuality, this outlined approach might be more feasible than the space elevator AND overcome a significantly large proportion of the energy costs requires for getting into space).  
If I have made an error in my reasoning, I would sure like to know.  
Also, perhaps (solar powered?) magnetic sails (that force against the Earth's magnetic field) could be used to reduce the weight induced tension along several points of the tether?  Perhaps more conventional thrust generation methods would relieve the tension allowable for a greater flexibility in material utilisation?  
A general point could be that the space elevator doesn't really need to take up into space at all in order to be economically viable – it just needs to get us 10% of the way up (aren't most of the energy hurdles in relation to leaving the Earth's gravitational field used up in making the first small proportion of the distance?).  
I have not done any calculations when making this post – though I do believe that the approximate figures given are unlikely to be terribly incorrect in principle at least.  
ConcernedScientist 01:22, 30 June 2007 (UTC)
replies: text: It's a reasonably good idea, but this isn't the place to discuss it.WolfKeeper 17:47, 14 July 2007 (UTC)
replies: text: I concur.  Though, with hindsight, I would refer the reader to Talk:Space elevator/Archive 6.  Here, the balloon idea was already mentioned.  I am not aware of any mention having been made concerning using high current conductors attached to the tether to induce a force due to the Earth's magnetic field (I know, the earth's magnetic field is probably only (0.3/16) Tesla's at any real appreciable distance from the surface - but it should still be feasible to generate a decent force capable of reducing tension within the tether so that carbon nanotube material isn't needed at all.  
(Consider F=BIL, and a long superconductor on a moving air based platform to see that Carbon Nanotubes might not be absolutely necessary).  
Anyhow, forgive my rambling, all of this is probably WP:NOR bound, so I'll stop making a mention of these ideas (though I doubt that they're Original Research as they are so obvious that someone must have posted them some time ago...).  
ConcernedScientist 00:59, 15 July 2007 (UTC)
thread_title:  Helium Balloons.  

message: I replaced the SVG diagram of the elevator with the original PNG one, because the SVG showed the elevator to go up from the north pole, which is nonsense. Many people don't intuitively understand why it has to go from the equator, because many don't understand the idea of an orbit. 79.120.55.7 07:01, 20 September 2007 (UTC)
replies: text: I'm glad I wasn't the first person to catch this mistake.  But it looks as though it's been reverted to the SVG.  The caption mentions a geosynchronous orbit but the picture does not reflect it.  I was so surprised I had to go back and check my physics ;) -Verdatum (talk) 18:21, 27 November 2007 (UTC)

text: OK, I fixed it, as well as various other places that were linking to the same image. -Verdatum (talk) 18:50, 27 November 2007 (UTC)
thread_title:  Image incorrect 

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

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