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The image says that the elevator should be in a geosynchronous orbit. Actually it should be in a geostationary orbit, which is different. Could somebody fix this please? 67.173.108.82 ( talk) 04:30, 8 March 2011 (UTC)
Once it's anchored, I'm not so sure it can be said to be in any type of orbit. It's just an upsidedown pendulum at that point. Only during initial deployment will it need to be in Geostationary orbit. Actually, when you think about it, that's true only during the last 80 miles or so when the bottom dips into the atmosphere. If we have the ability to adroitly maneuver the whole thing when it's fully extended (~100,000 km), then there isn't even a need to be geostationary/geosynchronous at all during deployment. Indeed, we will need at least some kind of maneuverability during deployment, that means some of the time the system won't be exactly geostationary. Skyway ( talk) 00:59, 2 April 2011 (UTC)
I fixed it with the new improved diagram I uploaded about 12 hours ago. It now says "Geostationary". Skyway ( talk) 19:28, 2 April 2011 (UTC)
It seems to me that "skyhook" being an alias for a "Space Elevator" might be a bit of a misnomer, as sky-hook is often used to refer to the apparatus seen in the most recent Batman movie - do we have a reference for "skyhook" in terms of a space elevator? 192.35.35.35 ( talk) 19:44, 17 February 2010 (UTC)
The section that begins as follows has OK analysis but wrong language: "Physical analysis [edit] Apparent gravitational field
In the rotating coordinate system whose origin is at Earth's center and turning with Earth's daily revolution, the acceleration of any static point in the equator's plane is:"
problem 1: if the point is "static" then the acceleration is zero and not the given formula. problem 2: this formula is really referring to the unit force per mass (gravitational force plus centrifugal force). If the unit force is zero then there is no acceleration, so setting this term equal to zero and solving yields the orbital radius at which a free-falling mass is static (in the rotational coordinate frame.) —Preceding unsigned comment added by Burressd ( talk • contribs) 21:35, 2 July 2010 (UTC)
While the physics section is reasonable, it also appears to be WP:OR. This is an encyclopedia, not a physics class tutorial, so the article should just summarise the findings of physicists on its feasibility. There is no need to walk the reader through the equations, step by step. Ashmoo ( talk) 11:52, 24 February 2011 (UTC)
I agree. Even calling it "Physics" is a distraction. "Mechanics" is what people need to understand. While is IS satisfying for one to write that stuff down for one's own understanding, it's more like pedanticism to cram anything more than the basic basics of equations down lay people's throats. All that stuff is really not encyclopedic. Skyway ( talk) 03:37, 2 April 2011 (UTC)
Yeah. I hear ya. And, I think your point of view is valid. I just disagree for all but the most basic of basic equations (like E=MC^2 or F=ma for example). It's a matter of where the line is drawn probably. On WP, so much of the "complete summary", when it includes equations, is done in a way that disengages the reader's otherwise rapt attention and "drinking in" of the material. So much of it really is a pedantic spewing by some 20-something male grad student. Okay, maybe the "spewing" isn't intentionally pedantic, rather it is an "admirable enthusiasm for the material" by the guy, but the style of the material often reads as pedantic and makes eyes glaze over. Expanding on what Ashmoo said, most equations in WP come off looking like a physics tutorial. It can usually be done better. It's often uncited "original research" too.
The "Apparent gravitational field" equations may fall into the category of basic of basic, but they need to be presented better. What better illustrates my point however, is the "Cable section" differential (differential!!) equations. These are not fundamental for a "complete summary". The fact that taper vastly increases the performance of the cable is fundamental, but the arcane details are not. (Actually, I think a small increase in the taper ratio of a simple linear taper has a much bigger effect than the same ratio turned into one of those "optimized" profiles. But I need to confirm that.) It is of greater importance that the cable will need to be fatter in the high micrometeor/spacejunk region than given for that uber-idealized arcane "perfect taper profile". That thicker section isn't mentioned, and it would drastically change the rest of the shape to be quite unlike the ideal form given. In fact, I think those equations and conclusions are indeed dubious for other reasons as well...
-- No mention is made of taper ratio (except for the changes I had made in the first paragraph of the section),
-- "reduces required strength by a third" is ambiguous.
-- No mention is made for the fact that the lower sections will need to be fatter to support climbers with the same safety margin. (With the focus on making perfect little equations, it got the design criteria all wrong.)
-- Actual cross-section design work will be done numerically anyway.
-- It is uncited and likely to be original research of the kind I've described above.
In other words, dubious.
So, now that you've gotten me thinking more deeply about it, I agree the "Apparent gravitational field" equations are good (with some fixes), but those "Cable section" equations really do need to go. Would you be okay with that? I am confident I can come up with something better about cross section that is well cited with reliable references. :-)
Skyway ( talk) 19:06, 2 April 2011 (UTC)
That's pretty tough talk, man. I've given thorough, hopefully tone-free, argument as to why the "Cable section" equations are dubious. They are obviously uncited. The same
WP:OR complaint has also been issued by at least one other. And you respond with a threat to summarily revert? Without justification? I don't think that's the way you work (I've checked). When I asked if you would be okay with it, I wasn't suggesting that you had go-no-go approval privileges. I was trying to be civil and cooperative, hoping to elicit some reasoned argument. You aren't the owner of this article, don't be trying to force your way by throwing weight around. Justify, dude!
There are two arguments here: 1) The applicability of equations in general, and 2) the validity and inclusion of the equations currently in "Cable section". We can disagree on question 1). Although I generally disfavor equations, I'm not hard-over on it, and I'm not on an anti-equation spree. So, don't worry about that. But, on question 2) I have made good arguments for the non-inclusion of those particular equations. I haven't seen any actual backed-up argument for inclusion. I seem to be supported as well by Ashmoo.
Instead of changing them right away, I'll just tag them "Citation needed" or "Dubious" or some such label if you prefer. Then we can let things settle a bit while others hopefully pipe in. Another alternative is to mention the equations as depicting the "idealized" taper form (like an ideal gas), but that a number of factors will require the design to deviate from this, then go on to talk about those factors and their influence on cross section form. If that were done, the equations would still need to satisfy the other criteria for inclusion (reliable references, etc.).
Yours, Skyway ( talk) 22:42, 2 April 2011 (UTC)
My change was reverted. The article currently states: "Once anchored, if the center of mass is moved upward to be above the level of geosynchronous orbit (by adding mass at the upper end or by paying out more cable), it will add a tension to the whole cable, which can then be used as an elevator cable."
This makes no sense. The center of mass is always above GEO once the cable is played out because centrifugal forces will require more mass above GEO to balance the gravitational forces below GEO. The correct term should be "center of weight" — Preceding unsigned comment added by Nydoc001 ( talk • contribs) 23:39, 12 August 2011 (UTC)
I like that this subject has come up and I applaud
Nydoc001 for having the courage to see that we get it right. I myself ponder over the correctness of CG vs. CM (or some other kind of "center") for space elevators. I'm airplane guy, and I'm used to CG and CM being interchangeable. Clearly, for space elevators, they are not. I've adopted the probably-correct convention of using "CM" as the place where, if all the mass of the free-flying very tall satellite (such as during deployment) were concentrated, the relevant orbital parameters (such as period) would be unchanged. But, I am unsure of this because I haven't yet sat down and worked it out for myself. The community of serious practitioners do use CM to describe that point and I have reason to trust them, but I won't have absolute trust in it until I get around to figuring it out myself!
CG vs. CM is important to get right. An actual explanation of the meanings and differences might be off-topic for this article, but the example of a space elevator might be right-on for the CG and CM articles.
Skyway ( talk) 20:49, 18 August 2011 (UTC)
Neato. I've come across Blaise Gassend's site before and found him to be very reliable. Yes, when anchored and operational, the "balance point" (whether it is a "CG", "CM", or other "center" -- "CM" for now) will need to be above GEO to provide "excess tension", or "ultimate lifting capacity", or "pull-down margin" - that 20 ton upward force you mention. So, things are different pre-anchored vs. post-anchored. During deployment, the system is in orbit. While anchored and operational, it is not in orbit, not one bit of it. During deployment, the "balance point" (presumably "CM") will need to be exactly at GEO level and over the equator if the deploying system is to remain over the anchor point. Personally, I'm not sure it needs to be perfectly stationary over the anchor point during deployment. Technically, such positioning is only really necessary during the last 100 km of the lowering of the lower "transponder" end. During deployment, we may want to let it precess East or West or let it increase or decrease it's period for whatever reasons we have at the time.
Skyway ( talk) 21:35, 18 August 2011 (UTC)
I'm starting to suspect you are right. THE reliable reference ("The Space Elevator" by Edwards and Westling) refers to the CM being at GEO during deployment for the system to remain stationary over a spot above the equator. But, I "did the math" last night and it looks like the point that needs to be at GEO is somewhere below CM and above CG. I did this analysis very quickly and I'm still in the process of verifying it, so definitely don't hold me to it! I suggest we keep the article saying "CM" for the time being. Even if you are right, I think the difference is probably small, and the correct idea still gets across. If we took our study and published it here it would clearly amount to original research, which is verboten in WP. It's definitely a cool thing to think about though.
Skyway ( talk) 19:20, 20 August 2011 (UTC)
I just re-read that reference you mentioned ( http://gassend.net/spaceelevator/center-of-mass/index.html) with new eyes. He confirms that the CM is above GEO even for an un-anchored (deploying, synchronous) SE. Now we can carefully review the text with this reference in our back pocket for misuse of "CM" where it implies that CM is at GEO during deploy. We don't need to go on to actually name that point though (unless there is a source for it). As an article about SEs and not a textbook about them, we don't actually have to go into that detail.
Skyway ( talk) 05:41, 21 August 2011 (UTC)
Eureka! I've found the missing link! The trouble we-all have been having is with the common use of "center of mass" in describing what's at geosynchronous orbit level. The modern-day bible (Edwards-Westling, "The Space Elevator") consistently uses this term, but we know that the CM must be above GEO if the period of a deploying system is to be one (sidereal) day. "How could the man get it wrong?" we all wonder. Well, check out the top half of page 72 of that reference:
"In our specific situation the geosynchronous orbit altitude for our center of mass depends on how much ribbon we have deployed."
So, Edwards redefines GEO level in some contexts to depend on the vertical mass distribution of very tall satellites. He is right, and we are technically correct to use "CM", but only if we make it clear that we are also using a variable definition of GEO. The big problem is that this subtlety is lost on most readers and editors, even non-lay readers/editors! So, too frequently, in fact almost always, people end up just describing the center of mass to be at the "normal" GEO level and not thinking about it too much - until someone (like Nydoc001) comes along and says "Hey! the emperor has no clothes!".
I suggest that this article picks only one method of describing the situation and keeps it consistent, lest we continue to confuse readers (and ourselves!).
Method A) Define "GEO" as non-varying and never state or imply that CM is at GEO, but is in fact above GEO for a deploying (yet un-anchored) system. Maybe we should put some hidden notes in the text warning future editors to not misinterpret Edwards' use of "CM at GEO".
Method B) Allow CM to be described as being at GEO for a deploying system as long as it is always clear that the "GEO" referred to in that context is not at the same level as "normal GEO".
I strongly favor Method A because "GEO" not being at the "normal" altitude is only applicable during deployment. In almost all other situations, such as normal use of a SE, GEO is right back at the normal level (where it belongs!). It would be confusing to let GEO move sometimes and not move other times.
Skyway ( talk) 19:08, 22 August 2011 (UTC)
I read Nydoc001's short-term edit with the short-lived new section (2 edits ago?) and it made me realize that there can be confusion as to exactly what objects are included in whatever we are considering the center of mass of. Here is the answer (I do declare! :-) ) :
During deployment the system includes:
1) The concentrated mass at the top, i.e. the spool including the portion of undeployed tether on it. When fully deployed, this mass along with additional mass added to it, is called the counterweight.
2) The thus-far deployed tether.
3) The concentrated mass at the bottom of the tether. I call this the "lower counterweight". It is the smaller spacecraft containing transponder for location, and rocketry for initial deployment (which is necessary until tidal forces can keep the tether taut). The mass of the transponder & rocketry will slightly pre-tension the tether. Additional "dead weight" might be added to further pretension the tether.
At the exact moment the "lower counterweight" is grabbed and affixed to the Earth, it becomes not part of the "system", and instantly the CM moves upward. This is somewhat mere re-definition (!), but not fully because the lower counterweight does transition from being free-flying as a part of a "tall satellite" to not being part of it and being fixed to the ground and constrained in it's movements. At this moment, the rest of the "tall satellite" (upper CW and tether) is no longer "in orbit" either (!), so it is also no longer a satellite because it is also constrained in it's movements (at the bottom) - an important point. At the moment the lower counterweight is grabbed, the tension that was on the tether just above the lower counterweight becomes the "excess tension"/"pull-down margin" of the system. This initial "excess tension" equals the weight of what was the "lower counterweight". After anchoring, as the spool continues with its remaining deployment upward, that initial "excess tension" at the bottom increases until the spool is fully deployed. With this now-greater "excess tension", the lower part of the tether can hold the first climbers.
While anchored to the ground the system includes:
1) The counterweight.
2) The tether.
3) All mass attached to the tether such as climbers, stations, etc.
When anchored, the system doesn't include that "lower counterweight" that was so important during deployment.
There you go everybody. Just wanted to clarify that point of confusion.
Skyway ( talk) 23:12, 18 August 2011 (UTC)
By "the system" I meant the collection of things that we are talking about the center of (gravity, mass, or whatever) of. I should have been more clear about that. Which kind of "center" wasn't my purpose. What "the system" should mean in this context was also not my purpose. I wanted to provide the practical information to you all that, when active modern practitioners say "CM", the control volume (CV) they are referring to is the CV I describe above.
Skyway ( talk) 05:31, 19 August 2011 (UTC)
Hi guys, I composed this while you were "talking", then had an edit conflict. I was responding to Nydoc001's 20:07 comment, but it applies to siafu.20:51 and Nydoc001.21:05 too...
Nydoc001, (your 20:07 comment) is true for the static situation, and true for the situation we are/were talking about with regard to the "balance point" being above GEO and all that. (For the dynamic situation, as in the contemplation of oscillations, any mass attached at GEO will definitely be material. But, dynamics is outside the topic for now. :-) ) Hmmm... let me think about that static (vertical) situation some more... I'm thinking you make a very good mind-expanding point. Now that I think about it, if a very very large mass (order of the whole SE) was just parked next to and not touching a cable at GEO, it is no different statically than if it was attached to the cable at GEO. The "excess tension"/"pull-down margin" will not change (just like you suggested). The CM will still be above GEO, but less so. Hmmm... Dang, you're making me think...
Okay, I have an answer for what it's worth. Here it is:
The distance from GEO upward to the center of mass is not a direct measure of resistance to being pulled down. That distance must be compensated somehow for mass (and maybe other factors) for it to be a measure of pull-down margin.
SO, what we are saying in the article is still true with regard to the CM being above GEO. The (above) descriptions of CV also still hold true. That large mass attached at GEO is in the CV when it is attached and is not in the CV when not attached, just like the CV definitions I described above. The pull-down margin is not changed even though the center of mass is changed (!). It's just that the amount that CM is above GEO is not a direct measure of pull-down margin. In the non-attached case, the distance from GEO to CM is compensated for by a lesser mass. In the attached case, the distance from GEO to CM is compensated for by a greater mass. In both cases, when compensated for mass, the pull-down margin will be the same. This makes sense because, at GEO, attaching adds no vertical force.
I think you've moved the bar, man. Space elevator engineering is a little further advanced today. (Seriously! :-) )
Skyway ( talk) 21:36, 19 August 2011 (UTC)
This space elevator article (and the carbon nanotube article it is partially based on) may be misleading on just comparing the strength of individual carbon nanotubes, atoms wide and defect free, to the aggregate strength of macro scale materials like commercial steel, kelvar, etc. See, for instance, monocrystalline whisker:
Typical whisker materials are graphite, alumina, iron, or silicon. Single-crystal whiskers of these (and some other) materials are noted for having very high tensile strength (on the order of 10–20 GPa). Whiskers are used in some composites, but large-scale fabrication of defect-free whiskers is very difficult. Prior to the discovery of carbon nanotubes, single-crystal whiskers had the highest tensile strength of any materials known, and were featured regularly in science fiction as materials for fabrication of space elevators, arcologies, and other large structures.
Many materials (iron, carbon graphite, silicon, etc.) can have around an order of magnitude higher strength in submicroscopic test samples than those materials do in practice on large scale for the macro-scale aggregate of quintillions of atoms, defects and all (where, in contrast, strengths drop to a fraction of a GPa to low single-digit GPa instead of the 10-20 GPa for the single-crystal whiskers).
Likewise, google any carbon nanotube composite or even carbon nanotube rope (of fraction of a millimeter or greater diameter) made in the decades since their discovery, and measured strengths range from a fraction of a GPa to single-digit GPa. The up to 50-150 GPa mentioned in the articles for test results is only for individual nanotubes, but very few people will learn the magnitude of the difference. Indirectly encouraging a space policy of waiting for CNT materials to hopefully later in our lifetimes get nearly the same strength on the aggregate macro scale that the best atoms-wide samples do (which has not happened with other materials) may be disadvantageous if the validity of the implicit assumptions behind such is in question.
24.253.194.197 ( talk) 7 May 2011 (UTC)
Has the effect of ultraviolet radiation and exposure to ionized forms of oxygen, nitrogen and NO on ribbon material been adequately examined? 184.66.110.161 ( talk) 03:20, 15 March 2012 (UTC)
Should the phrase "transit times are expected to be long enough where, if unshielded, total exposure would be above levels considered safe." be rather "transit times are expected to be long enough where, if unshielded, total exposure would be above levels considered unsafe."? — Preceding unsigned comment added by 175.39.42.46 ( talk) 10:18, 29 March 2012 (UTC)
Some phrases in the "21st century" section are in a different font and without spaces. For example "which featured US500,000awardsforeachofthetwocompetitions,(US1,000,000 total)". I can't see what it's caused by and do not find manual editing reliable enough to re-type the text without typos. What is the problem here, exactly? -- Gryllida 02:07, 22 May 2012 (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.
Skyway ( talk) 09:37, 2 April 2011 (UTC)
While the length of the cable may be to scale, the size of the chamber and counterweight most certainly aren't. The figure caption should be updated to reflect this. — Preceding unsigned comment added by 203.206.172.171 ( talk) 01:54, 14 July 2012 (UTC)
It would be good to have a section explaining why the orbit (or path) of the counterweight remains stable despite the extra forces acting on it when the climber moves up. This is a central question because otherwise the entire concept of a space elevator wouldn't be feasable. And indeed from a naive perspective one would expect that the horizontal speed the payload gets for "free" when moving up is not only taken from the earth's roational energy but also from the counterweight's kinetic energy which would in turn cause its orbit to decay every time a payload is moved up. — Preceding unsigned comment added by 92.20.87.48 ( talk) 10:11, 28 August 2012 (UTC)
What exactly would the effect be of the space elevator on the orbit of the earth itself (earth's orbit around the sun) ? Could it pull the earth of it's trajectory (similar to a rocket near an asteroid effecting the path of an asteroid, ie see article on impact event) 91.182.27.70 ( talk) 08:17, 12 July 2012 (UTC)
Although this article is fascinating I was intrigued that there was no mention of Earth weather conditions that would be experienced by the tether - say the effects of a lightning strike on the line (yes it may be an opportunity to charge massive capacitors and power the operation of the elevator ... but is there any chance it would survive? ... would the geostationary component need thrusters as a back-up? would multiple separate tethers help?) - or the impact of a tether going through a twister?
Is it worth mentioning as issues to be considered later? WKChris ( talk) —Preceding undated comment added 09:02, 7 September 2013 (UTC)
There may be a stability problem with objects on the space elevator. If the horizontal velocity is reduced they will fall to a lower orbit. To get back to LEO from GEO a free flying object needs a delta-V of 3.9 km/s to slow them down. Objects going above GEO need a gain of delta-v. However if an object is attached to the ribbon then an exchange of velocity can occur. Consequently objects can move with only a small motor providing they follow gravity. Such movement can be unintentional and may enter a feed back loop. The climbers need to be equipped with brakes.
Andrew Swallow ( talk) 19:11, 10 February 2014 (UTC)
..available here LeadSongDog come howl! 16:58, 26 February 2014 (UTC)
Hi guys, I'm seeing a lot of fast reverts in the last few days. I think we should go easy with them. A fast revert carries along with it a slap in the face to the person who is reverted. It shouldn't, but it does (we're all weak human beings like that, especially us males). Some of the edits this has been done to have been trivial ones that could have been better left alone or simply modified with some nice words in the the edit summary. The kick in the nuts that goes along with reverts has been exacerbated by uncivil nasties in the edit summaries. Let's knock it off. Skyway ( talk) 16:37, 6 April 2014 (UTC)
A citation was needed on the formula. How about: [1] Robin.Randall 1:03 9 July 2015 (UTC) — Preceding unsigned comment added by 128.107.163.58 ( talk)
Edit comment: Try this on for size. Made more clear that cable is frame of ref, "accelerate" no longer a tripping hazard. "Up/Down" is more general (not specific to Earth. The term "geosynchronous" is already specific to Earth, so trying to avoid saying Earth in the rest of the description is futile.
The more accurate way to describe this is that an object released from a space elevator below the synchronous orbit point will enter an elliptical orbit with the highest point being where it was released from the cable. An object released from a space elevator above the synchronous orbit point will enter an elliptical or hyperbolic orbit with the lowest point being where it was released from the cable.
Regrettably, the above sentence while general and accurate, is much less understandable. You're better off using earth-centered terminology (perigee, geosynchronous, ect.). Tarl.Neustaedter ( talk) 05:40, 14 May 2014 (UTC)
Take a break, Tarl. How much time did you spend on that bit of "nitpicking"? (eye roll) Skyway ( talk) 06:17, 14 May 2014 (UTC)
I see that some people discussing "What are the Constraints on Building a Tower to Space?" seem to think that the sheer mass of the cable makes it impossible.
Could someone please add to this article the total mass of space elevator? Preferably both the initial "seed cable" mass and the much larger "finished cable" mass?
Would it be relevant to compare that mass to the total mass of all the stuff people have already installed in geostationary orbit, including the stuff that has since been moved to a graveyard orbit? Would it be relevant to compare that mass to the total mass of a recent year's production of natural gas? (Natural gas is the raw feedstock for most recent nanotube production, right?) -- DavidCary ( talk) 08:42, 6 January 2013 (UTC)
I think finding out what confusions or misconceptions people have about space elevators then adjusting the article accordingly is a good thing. This article is the "go to" place where most people get all of what they know about Space Elevators. If there is a prevalent idea out there that SEs would be impossibly massive, we should make sure it's addressed in the article. We should probably cite something showing that reasonably anticipated designs require only a small number of large rocket launches (as DavidCary made a start on).
Skyway (
talk) 03:21, 8 January 2013 (UTC)
It seems to me it would be appropriate to discuss the need for two cables (or a wide web) to be built to efficiently allow an up climber and a down climber to pass each other. Two cables would lower the risk and allow maintenance on one while the other could be productive. The alternative would be to show how an up and down climber could pass at 300mph on one cable. 67.188.92.176 ( talk) 21:19, 01 June 2014 (UTC)
Hi there, I fixed an error here which someone has reverted.
https://en.wikipedia.org/?title=Space_elevator&oldid=612291048&diff=prev
I agree that it may well be going off topic - but the original text without my qualification in the next paragraph gives the false impression that you can return the materials of an asteroid back to Earth using a spinning tether. Instead, if it was, say, a million ton asteroid, you might be able to return one or two hundred tons this way - not worth the effort involved in building a space elevator. It might be worth doing for returning a sample.
So - what's the solution? Perhaps leave out the idea of using a space elevator on a spinning asteroid for mining?
But a space elevator could be used on a large enough asteroid say Ceres. The thing is you can't use it to mine a significant fraction of the mass of the asteroid or you will despin it completely. But you can use it for a very small scale mining operation of a few tons, or for a large scale mining operation on a very large asteroid.
Anyway don't think I'll attempt to edit again, but maybe someone esle can sort this out, so adding this note here with the information I found out.
I got confused by the statement originally - and actually wrote in one of my own articles that you can use a spinning tether for asteroid mining, without qualification, but couldn't remember where I read it and searching for the reference eventually traced it back ehre - and to the linked article, and then on careful reading of the linked article realized you can only extract a tiny fraction of the mass of an asteroid in this way - so wanted to correct the article so others reading it would not get the same false impression I got . Robert Walker ( talk) 00:17, 11 June 2014 (UTC)
Valid complaint. Check out the attempt to subdue "bulk" without adding too many words supporting what is a fairly minor mention. 100.0.101.252 ( talk) 16:59, 11 June 2014 (UTC)
Whoever wrote the Space Elevator article should update it so that it references William Forstchen's 2014 book, Pillar To The Sky. The book should be read and the imaginings of how this technology could be implemented should be summarized. — Preceding unsigned comment added by 24.2.86.57 ( talk) 02:40, 20 June 2014 (UTC)
The reason Yobot removes <small> tags from image descriptions: Error 66 - The description is already set to 94% in the stylesheet. This causes problems with people who have trouble reading small print. In other words, the fact that it may look nicer to you and I doesn't mean it's accessible to someone with vision problems. Tarl.Neustaedter ( talk) 14:58, 9 July 2014 (UTC)
I believe ksj.mit.edu is a reliable source and demonstrates a brief mention is due. -- Ronz ( talk) 15:13, 1 August 2014 (UTC
The ribbon thickness and material strength equations are labelled as original research. I have seen them on a website. I wish to remove the label. Have the equations occurred in a formal paper or textbook? Andrew Swallow ( talk) 04:42, 9 January 2013 (UTC)
user: Skyway, I assume you can bear the responsibility for maintaining a sign error in that section - not to mention other problems. Well - your problem, not mine, I was just trying to improve that encyclopedia. But, then, when Huns are on the loose, scholars can but hide away. Biem ( talk) 20:05, 21 November 2014 (UTC)
Now, since that integration is but plain calculus and beaten track, is there an objection to move the "section OR" flag down to the sentence "It turns out that between these two points, this quantity can be expressed simply" - in order to point more accurately to the point where it ceases to be beaten track and may indeed be somehow personal development (though neither false, nor reasearch level) ? Biem ( talk) 13:50, 5 December 2014 (UTC)
OK :
Biem ( talk) 19:57, 6 December 2014 (UTC)
OK, I think your objection (though per se legitimate) is out of purpose in this case :
Thus, as I see it,an integration of that differential equation cannot be considered as an original research, it is just in that case a redaction work needed to present to the layman reader facts already known (and used in the article), and understand why the initial equation (documented) relates to other facts presented in the article, and leads to a very strong constraint on the material used for the space elevator tether (which is important for the comprehension of the issue).
Biem ( talk) 22:54, 6 December 2014 (UTC)
Unless you have a stronger argument related to the "original research" problematic, I shall therefore move the "section OR" flag down to the sentence "It turns out that between these two points, this quantity can be expressed simply", and let you flag the equations with whatever "reference needed" you may wish to add. Biem ( talk) 23:15, 7 December 2014 (UTC)
Wikipedia articles must not contain original research. The phrase "original research" (OR) is used on Wikipedia to refer to material—such as facts, allegations, and ideas—for which no reliable, published sources exist. This includes any analysis or synthesis of published material that serves to reach or imply a conclusion not stated by the sources. To demonstrate that you are not adding OR, you must be able to cite reliable, published sources that are directly related to the topic of the article, and directly support the material being presented. (This policy of no original research does not apply to talk pages.)
The prohibition against OR means that all material added to articles must be attributable to a reliable published source, even if not actually attributed. [...]
Your reasoning is going the wrong way : "Published => Not OR" is not equivalent to "not published => OR", you are taking it for an equivalence which is a common mistake. But anyway, as stated above : * The basic differential equations are those published in the paper cited, The physics of the space elevator. They have already been referenced in the article, and cannot be considered as OR. Biem ( talk) 07:29, 8 December 2014 (UTC)
OK, if that equation is part of those published in the paper cited, The physics of the space elevator: is it acceptable to cite them as such, translate the "OR" flag and move forward to the next section?
Biem ( talk) 18:57, 8 December 2014 (UTC)
Guys, the offending uncited and dubious (and pedantic IMHO) text has been been tagged so for more than two years. Any of us would be completely justified in immediately removing it altogether. I am tempted to do just that. Then, according to
WP:burden, it could not be reinstated without the (now) required citations. But, I think removal would be harmful because that idealized cross section curve is indeed historically notable in the development of space elevator designs. I also think removal isn't really necessary because there are lots of refs out there for this. It's just a matter of investing time into going out and getting them.
To start with, it looks to me like that name="aravind" ref (PKASpace Elevators.pdf) could do the job of justifying removal of the larger OR tag. Having perused the ref, it looks pretty good for covering the "constant stress" postulate at least. Someone would have to look at it closer to see if it covers the "pedantic integration" and the resulting curve (though it probably does). I'll put that ref in to cover the integration and the resulting curve as well as "constant stress", then I'll remove the tag and see how it goes. I'd still like to see an additional discussion on the modern cross section shapes, but at least there is some wording saying that the given curve is "idealized", so that will have to do for now.
Skyway (
talk) 20:40, 8 December 2014 (UTC)
You're right. Citations are always better when they give specific pages, paragraphs, etc.. Citing the paper as a whole is more vague, but better than no citation I think. It's also a step, small or large, on the way to betterment. Other sources could be found and cited too. Anyone up for any of that? Until that better state is achieved, the current state (imperfect citing, no section tag) is probably better (less controversial too) than the previous state (no cites, section tag). Eh? Skyway ( talk) 04:04, 9 December 2014 (UTC)
Over the last few hours I've given that paper a closer look too and indeed it doesn't give our equations exactly. A good source should. I agree with Tarl there. One problem is that each source states the same idea or equation almost always somewhat differently than the others. Ultimately, the more equationeering done here, the harder to find exact duplicates in the sources, and making it especially hard to use more than one source. That's (yet) another argument for removing the "pedantic integration" and only mentioning 1) the "constant stress" starting point (easy multiple sources), and 2) the complicated resulting S(r) equation taken from one of the sources. That way we don't have to source "g=GM/r2" or any of the other intermediary pedantic bullshit -- just delete the middle garbage! :-) Still, I'd like to keep that imperfect source there for the time being (to stave off the section tag) while we find better sources and do some other rewording. Skyway ( talk) 07:25, 9 December 2014 (UTC)
Suggestion to replace it with the correct link, http://www.thetimes.co.uk/tto/news/world/article1967078.ece — Preceding unsigned comment added by Katacarbix ( talk • contribs) 16:36, 27 March 2015 (UTC)
A security point. If diamond nanothreads are used in the space elevator do NOT call them diamonds. Otherwise every burglar and mugger within a 1000 miles will try to finance his drug habit by stealing some and fencing it at the local jeweller. Calling it crystalline carbon will fool most of them. Andrew Swallow ( talk) 20:57, 3 April 2015 (UTC)
Anyone mind if I set up this talk page for automatic archiving (MiszaBot)? I'd just create archive_9, but this page gets long enough that it's probably worth automatically archiving discussions which haven't been active for over 30 days. Tarl.Neustaedter ( talk) 04:58, 16 March 2015 (UTC)
somehow by placing a rail around equator to atach it to in both ends — Preceding unsigned comment added by 181.128.21.174 ( talk) 11:16, 17 February 2015 (UTC)
This should be removed. Please link to research not wonder aloud. 2601:5:9380:6E:D955:EC7F:4858:8AAD ( talk) 05:49, 6 April 2015 (UTC)
This page 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. |
The image says that the elevator should be in a geosynchronous orbit. Actually it should be in a geostationary orbit, which is different. Could somebody fix this please? 67.173.108.82 ( talk) 04:30, 8 March 2011 (UTC)
Once it's anchored, I'm not so sure it can be said to be in any type of orbit. It's just an upsidedown pendulum at that point. Only during initial deployment will it need to be in Geostationary orbit. Actually, when you think about it, that's true only during the last 80 miles or so when the bottom dips into the atmosphere. If we have the ability to adroitly maneuver the whole thing when it's fully extended (~100,000 km), then there isn't even a need to be geostationary/geosynchronous at all during deployment. Indeed, we will need at least some kind of maneuverability during deployment, that means some of the time the system won't be exactly geostationary. Skyway ( talk) 00:59, 2 April 2011 (UTC)
I fixed it with the new improved diagram I uploaded about 12 hours ago. It now says "Geostationary". Skyway ( talk) 19:28, 2 April 2011 (UTC)
It seems to me that "skyhook" being an alias for a "Space Elevator" might be a bit of a misnomer, as sky-hook is often used to refer to the apparatus seen in the most recent Batman movie - do we have a reference for "skyhook" in terms of a space elevator? 192.35.35.35 ( talk) 19:44, 17 February 2010 (UTC)
The section that begins as follows has OK analysis but wrong language: "Physical analysis [edit] Apparent gravitational field
In the rotating coordinate system whose origin is at Earth's center and turning with Earth's daily revolution, the acceleration of any static point in the equator's plane is:"
problem 1: if the point is "static" then the acceleration is zero and not the given formula. problem 2: this formula is really referring to the unit force per mass (gravitational force plus centrifugal force). If the unit force is zero then there is no acceleration, so setting this term equal to zero and solving yields the orbital radius at which a free-falling mass is static (in the rotational coordinate frame.) —Preceding unsigned comment added by Burressd ( talk • contribs) 21:35, 2 July 2010 (UTC)
While the physics section is reasonable, it also appears to be WP:OR. This is an encyclopedia, not a physics class tutorial, so the article should just summarise the findings of physicists on its feasibility. There is no need to walk the reader through the equations, step by step. Ashmoo ( talk) 11:52, 24 February 2011 (UTC)
I agree. Even calling it "Physics" is a distraction. "Mechanics" is what people need to understand. While is IS satisfying for one to write that stuff down for one's own understanding, it's more like pedanticism to cram anything more than the basic basics of equations down lay people's throats. All that stuff is really not encyclopedic. Skyway ( talk) 03:37, 2 April 2011 (UTC)
Yeah. I hear ya. And, I think your point of view is valid. I just disagree for all but the most basic of basic equations (like E=MC^2 or F=ma for example). It's a matter of where the line is drawn probably. On WP, so much of the "complete summary", when it includes equations, is done in a way that disengages the reader's otherwise rapt attention and "drinking in" of the material. So much of it really is a pedantic spewing by some 20-something male grad student. Okay, maybe the "spewing" isn't intentionally pedantic, rather it is an "admirable enthusiasm for the material" by the guy, but the style of the material often reads as pedantic and makes eyes glaze over. Expanding on what Ashmoo said, most equations in WP come off looking like a physics tutorial. It can usually be done better. It's often uncited "original research" too.
The "Apparent gravitational field" equations may fall into the category of basic of basic, but they need to be presented better. What better illustrates my point however, is the "Cable section" differential (differential!!) equations. These are not fundamental for a "complete summary". The fact that taper vastly increases the performance of the cable is fundamental, but the arcane details are not. (Actually, I think a small increase in the taper ratio of a simple linear taper has a much bigger effect than the same ratio turned into one of those "optimized" profiles. But I need to confirm that.) It is of greater importance that the cable will need to be fatter in the high micrometeor/spacejunk region than given for that uber-idealized arcane "perfect taper profile". That thicker section isn't mentioned, and it would drastically change the rest of the shape to be quite unlike the ideal form given. In fact, I think those equations and conclusions are indeed dubious for other reasons as well...
-- No mention is made of taper ratio (except for the changes I had made in the first paragraph of the section),
-- "reduces required strength by a third" is ambiguous.
-- No mention is made for the fact that the lower sections will need to be fatter to support climbers with the same safety margin. (With the focus on making perfect little equations, it got the design criteria all wrong.)
-- Actual cross-section design work will be done numerically anyway.
-- It is uncited and likely to be original research of the kind I've described above.
In other words, dubious.
So, now that you've gotten me thinking more deeply about it, I agree the "Apparent gravitational field" equations are good (with some fixes), but those "Cable section" equations really do need to go. Would you be okay with that? I am confident I can come up with something better about cross section that is well cited with reliable references. :-)
Skyway ( talk) 19:06, 2 April 2011 (UTC)
That's pretty tough talk, man. I've given thorough, hopefully tone-free, argument as to why the "Cable section" equations are dubious. They are obviously uncited. The same
WP:OR complaint has also been issued by at least one other. And you respond with a threat to summarily revert? Without justification? I don't think that's the way you work (I've checked). When I asked if you would be okay with it, I wasn't suggesting that you had go-no-go approval privileges. I was trying to be civil and cooperative, hoping to elicit some reasoned argument. You aren't the owner of this article, don't be trying to force your way by throwing weight around. Justify, dude!
There are two arguments here: 1) The applicability of equations in general, and 2) the validity and inclusion of the equations currently in "Cable section". We can disagree on question 1). Although I generally disfavor equations, I'm not hard-over on it, and I'm not on an anti-equation spree. So, don't worry about that. But, on question 2) I have made good arguments for the non-inclusion of those particular equations. I haven't seen any actual backed-up argument for inclusion. I seem to be supported as well by Ashmoo.
Instead of changing them right away, I'll just tag them "Citation needed" or "Dubious" or some such label if you prefer. Then we can let things settle a bit while others hopefully pipe in. Another alternative is to mention the equations as depicting the "idealized" taper form (like an ideal gas), but that a number of factors will require the design to deviate from this, then go on to talk about those factors and their influence on cross section form. If that were done, the equations would still need to satisfy the other criteria for inclusion (reliable references, etc.).
Yours, Skyway ( talk) 22:42, 2 April 2011 (UTC)
My change was reverted. The article currently states: "Once anchored, if the center of mass is moved upward to be above the level of geosynchronous orbit (by adding mass at the upper end or by paying out more cable), it will add a tension to the whole cable, which can then be used as an elevator cable."
This makes no sense. The center of mass is always above GEO once the cable is played out because centrifugal forces will require more mass above GEO to balance the gravitational forces below GEO. The correct term should be "center of weight" — Preceding unsigned comment added by Nydoc001 ( talk • contribs) 23:39, 12 August 2011 (UTC)
I like that this subject has come up and I applaud
Nydoc001 for having the courage to see that we get it right. I myself ponder over the correctness of CG vs. CM (or some other kind of "center") for space elevators. I'm airplane guy, and I'm used to CG and CM being interchangeable. Clearly, for space elevators, they are not. I've adopted the probably-correct convention of using "CM" as the place where, if all the mass of the free-flying very tall satellite (such as during deployment) were concentrated, the relevant orbital parameters (such as period) would be unchanged. But, I am unsure of this because I haven't yet sat down and worked it out for myself. The community of serious practitioners do use CM to describe that point and I have reason to trust them, but I won't have absolute trust in it until I get around to figuring it out myself!
CG vs. CM is important to get right. An actual explanation of the meanings and differences might be off-topic for this article, but the example of a space elevator might be right-on for the CG and CM articles.
Skyway ( talk) 20:49, 18 August 2011 (UTC)
Neato. I've come across Blaise Gassend's site before and found him to be very reliable. Yes, when anchored and operational, the "balance point" (whether it is a "CG", "CM", or other "center" -- "CM" for now) will need to be above GEO to provide "excess tension", or "ultimate lifting capacity", or "pull-down margin" - that 20 ton upward force you mention. So, things are different pre-anchored vs. post-anchored. During deployment, the system is in orbit. While anchored and operational, it is not in orbit, not one bit of it. During deployment, the "balance point" (presumably "CM") will need to be exactly at GEO level and over the equator if the deploying system is to remain over the anchor point. Personally, I'm not sure it needs to be perfectly stationary over the anchor point during deployment. Technically, such positioning is only really necessary during the last 100 km of the lowering of the lower "transponder" end. During deployment, we may want to let it precess East or West or let it increase or decrease it's period for whatever reasons we have at the time.
Skyway ( talk) 21:35, 18 August 2011 (UTC)
I'm starting to suspect you are right. THE reliable reference ("The Space Elevator" by Edwards and Westling) refers to the CM being at GEO during deployment for the system to remain stationary over a spot above the equator. But, I "did the math" last night and it looks like the point that needs to be at GEO is somewhere below CM and above CG. I did this analysis very quickly and I'm still in the process of verifying it, so definitely don't hold me to it! I suggest we keep the article saying "CM" for the time being. Even if you are right, I think the difference is probably small, and the correct idea still gets across. If we took our study and published it here it would clearly amount to original research, which is verboten in WP. It's definitely a cool thing to think about though.
Skyway ( talk) 19:20, 20 August 2011 (UTC)
I just re-read that reference you mentioned ( http://gassend.net/spaceelevator/center-of-mass/index.html) with new eyes. He confirms that the CM is above GEO even for an un-anchored (deploying, synchronous) SE. Now we can carefully review the text with this reference in our back pocket for misuse of "CM" where it implies that CM is at GEO during deploy. We don't need to go on to actually name that point though (unless there is a source for it). As an article about SEs and not a textbook about them, we don't actually have to go into that detail.
Skyway ( talk) 05:41, 21 August 2011 (UTC)
Eureka! I've found the missing link! The trouble we-all have been having is with the common use of "center of mass" in describing what's at geosynchronous orbit level. The modern-day bible (Edwards-Westling, "The Space Elevator") consistently uses this term, but we know that the CM must be above GEO if the period of a deploying system is to be one (sidereal) day. "How could the man get it wrong?" we all wonder. Well, check out the top half of page 72 of that reference:
"In our specific situation the geosynchronous orbit altitude for our center of mass depends on how much ribbon we have deployed."
So, Edwards redefines GEO level in some contexts to depend on the vertical mass distribution of very tall satellites. He is right, and we are technically correct to use "CM", but only if we make it clear that we are also using a variable definition of GEO. The big problem is that this subtlety is lost on most readers and editors, even non-lay readers/editors! So, too frequently, in fact almost always, people end up just describing the center of mass to be at the "normal" GEO level and not thinking about it too much - until someone (like Nydoc001) comes along and says "Hey! the emperor has no clothes!".
I suggest that this article picks only one method of describing the situation and keeps it consistent, lest we continue to confuse readers (and ourselves!).
Method A) Define "GEO" as non-varying and never state or imply that CM is at GEO, but is in fact above GEO for a deploying (yet un-anchored) system. Maybe we should put some hidden notes in the text warning future editors to not misinterpret Edwards' use of "CM at GEO".
Method B) Allow CM to be described as being at GEO for a deploying system as long as it is always clear that the "GEO" referred to in that context is not at the same level as "normal GEO".
I strongly favor Method A because "GEO" not being at the "normal" altitude is only applicable during deployment. In almost all other situations, such as normal use of a SE, GEO is right back at the normal level (where it belongs!). It would be confusing to let GEO move sometimes and not move other times.
Skyway ( talk) 19:08, 22 August 2011 (UTC)
I read Nydoc001's short-term edit with the short-lived new section (2 edits ago?) and it made me realize that there can be confusion as to exactly what objects are included in whatever we are considering the center of mass of. Here is the answer (I do declare! :-) ) :
During deployment the system includes:
1) The concentrated mass at the top, i.e. the spool including the portion of undeployed tether on it. When fully deployed, this mass along with additional mass added to it, is called the counterweight.
2) The thus-far deployed tether.
3) The concentrated mass at the bottom of the tether. I call this the "lower counterweight". It is the smaller spacecraft containing transponder for location, and rocketry for initial deployment (which is necessary until tidal forces can keep the tether taut). The mass of the transponder & rocketry will slightly pre-tension the tether. Additional "dead weight" might be added to further pretension the tether.
At the exact moment the "lower counterweight" is grabbed and affixed to the Earth, it becomes not part of the "system", and instantly the CM moves upward. This is somewhat mere re-definition (!), but not fully because the lower counterweight does transition from being free-flying as a part of a "tall satellite" to not being part of it and being fixed to the ground and constrained in it's movements. At this moment, the rest of the "tall satellite" (upper CW and tether) is no longer "in orbit" either (!), so it is also no longer a satellite because it is also constrained in it's movements (at the bottom) - an important point. At the moment the lower counterweight is grabbed, the tension that was on the tether just above the lower counterweight becomes the "excess tension"/"pull-down margin" of the system. This initial "excess tension" equals the weight of what was the "lower counterweight". After anchoring, as the spool continues with its remaining deployment upward, that initial "excess tension" at the bottom increases until the spool is fully deployed. With this now-greater "excess tension", the lower part of the tether can hold the first climbers.
While anchored to the ground the system includes:
1) The counterweight.
2) The tether.
3) All mass attached to the tether such as climbers, stations, etc.
When anchored, the system doesn't include that "lower counterweight" that was so important during deployment.
There you go everybody. Just wanted to clarify that point of confusion.
Skyway ( talk) 23:12, 18 August 2011 (UTC)
By "the system" I meant the collection of things that we are talking about the center of (gravity, mass, or whatever) of. I should have been more clear about that. Which kind of "center" wasn't my purpose. What "the system" should mean in this context was also not my purpose. I wanted to provide the practical information to you all that, when active modern practitioners say "CM", the control volume (CV) they are referring to is the CV I describe above.
Skyway ( talk) 05:31, 19 August 2011 (UTC)
Hi guys, I composed this while you were "talking", then had an edit conflict. I was responding to Nydoc001's 20:07 comment, but it applies to siafu.20:51 and Nydoc001.21:05 too...
Nydoc001, (your 20:07 comment) is true for the static situation, and true for the situation we are/were talking about with regard to the "balance point" being above GEO and all that. (For the dynamic situation, as in the contemplation of oscillations, any mass attached at GEO will definitely be material. But, dynamics is outside the topic for now. :-) ) Hmmm... let me think about that static (vertical) situation some more... I'm thinking you make a very good mind-expanding point. Now that I think about it, if a very very large mass (order of the whole SE) was just parked next to and not touching a cable at GEO, it is no different statically than if it was attached to the cable at GEO. The "excess tension"/"pull-down margin" will not change (just like you suggested). The CM will still be above GEO, but less so. Hmmm... Dang, you're making me think...
Okay, I have an answer for what it's worth. Here it is:
The distance from GEO upward to the center of mass is not a direct measure of resistance to being pulled down. That distance must be compensated somehow for mass (and maybe other factors) for it to be a measure of pull-down margin.
SO, what we are saying in the article is still true with regard to the CM being above GEO. The (above) descriptions of CV also still hold true. That large mass attached at GEO is in the CV when it is attached and is not in the CV when not attached, just like the CV definitions I described above. The pull-down margin is not changed even though the center of mass is changed (!). It's just that the amount that CM is above GEO is not a direct measure of pull-down margin. In the non-attached case, the distance from GEO to CM is compensated for by a lesser mass. In the attached case, the distance from GEO to CM is compensated for by a greater mass. In both cases, when compensated for mass, the pull-down margin will be the same. This makes sense because, at GEO, attaching adds no vertical force.
I think you've moved the bar, man. Space elevator engineering is a little further advanced today. (Seriously! :-) )
Skyway ( talk) 21:36, 19 August 2011 (UTC)
This space elevator article (and the carbon nanotube article it is partially based on) may be misleading on just comparing the strength of individual carbon nanotubes, atoms wide and defect free, to the aggregate strength of macro scale materials like commercial steel, kelvar, etc. See, for instance, monocrystalline whisker:
Typical whisker materials are graphite, alumina, iron, or silicon. Single-crystal whiskers of these (and some other) materials are noted for having very high tensile strength (on the order of 10–20 GPa). Whiskers are used in some composites, but large-scale fabrication of defect-free whiskers is very difficult. Prior to the discovery of carbon nanotubes, single-crystal whiskers had the highest tensile strength of any materials known, and were featured regularly in science fiction as materials for fabrication of space elevators, arcologies, and other large structures.
Many materials (iron, carbon graphite, silicon, etc.) can have around an order of magnitude higher strength in submicroscopic test samples than those materials do in practice on large scale for the macro-scale aggregate of quintillions of atoms, defects and all (where, in contrast, strengths drop to a fraction of a GPa to low single-digit GPa instead of the 10-20 GPa for the single-crystal whiskers).
Likewise, google any carbon nanotube composite or even carbon nanotube rope (of fraction of a millimeter or greater diameter) made in the decades since their discovery, and measured strengths range from a fraction of a GPa to single-digit GPa. The up to 50-150 GPa mentioned in the articles for test results is only for individual nanotubes, but very few people will learn the magnitude of the difference. Indirectly encouraging a space policy of waiting for CNT materials to hopefully later in our lifetimes get nearly the same strength on the aggregate macro scale that the best atoms-wide samples do (which has not happened with other materials) may be disadvantageous if the validity of the implicit assumptions behind such is in question.
24.253.194.197 ( talk) 7 May 2011 (UTC)
Has the effect of ultraviolet radiation and exposure to ionized forms of oxygen, nitrogen and NO on ribbon material been adequately examined? 184.66.110.161 ( talk) 03:20, 15 March 2012 (UTC)
Should the phrase "transit times are expected to be long enough where, if unshielded, total exposure would be above levels considered safe." be rather "transit times are expected to be long enough where, if unshielded, total exposure would be above levels considered unsafe."? — Preceding unsigned comment added by 175.39.42.46 ( talk) 10:18, 29 March 2012 (UTC)
Some phrases in the "21st century" section are in a different font and without spaces. For example "which featured US500,000awardsforeachofthetwocompetitions,(US1,000,000 total)". I can't see what it's caused by and do not find manual editing reliable enough to re-type the text without typos. What is the problem here, exactly? -- Gryllida 02:07, 22 May 2012 (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.
Skyway ( talk) 09:37, 2 April 2011 (UTC)
While the length of the cable may be to scale, the size of the chamber and counterweight most certainly aren't. The figure caption should be updated to reflect this. — Preceding unsigned comment added by 203.206.172.171 ( talk) 01:54, 14 July 2012 (UTC)
It would be good to have a section explaining why the orbit (or path) of the counterweight remains stable despite the extra forces acting on it when the climber moves up. This is a central question because otherwise the entire concept of a space elevator wouldn't be feasable. And indeed from a naive perspective one would expect that the horizontal speed the payload gets for "free" when moving up is not only taken from the earth's roational energy but also from the counterweight's kinetic energy which would in turn cause its orbit to decay every time a payload is moved up. — Preceding unsigned comment added by 92.20.87.48 ( talk) 10:11, 28 August 2012 (UTC)
What exactly would the effect be of the space elevator on the orbit of the earth itself (earth's orbit around the sun) ? Could it pull the earth of it's trajectory (similar to a rocket near an asteroid effecting the path of an asteroid, ie see article on impact event) 91.182.27.70 ( talk) 08:17, 12 July 2012 (UTC)
Although this article is fascinating I was intrigued that there was no mention of Earth weather conditions that would be experienced by the tether - say the effects of a lightning strike on the line (yes it may be an opportunity to charge massive capacitors and power the operation of the elevator ... but is there any chance it would survive? ... would the geostationary component need thrusters as a back-up? would multiple separate tethers help?) - or the impact of a tether going through a twister?
Is it worth mentioning as issues to be considered later? WKChris ( talk) —Preceding undated comment added 09:02, 7 September 2013 (UTC)
There may be a stability problem with objects on the space elevator. If the horizontal velocity is reduced they will fall to a lower orbit. To get back to LEO from GEO a free flying object needs a delta-V of 3.9 km/s to slow them down. Objects going above GEO need a gain of delta-v. However if an object is attached to the ribbon then an exchange of velocity can occur. Consequently objects can move with only a small motor providing they follow gravity. Such movement can be unintentional and may enter a feed back loop. The climbers need to be equipped with brakes.
Andrew Swallow ( talk) 19:11, 10 February 2014 (UTC)
..available here LeadSongDog come howl! 16:58, 26 February 2014 (UTC)
Hi guys, I'm seeing a lot of fast reverts in the last few days. I think we should go easy with them. A fast revert carries along with it a slap in the face to the person who is reverted. It shouldn't, but it does (we're all weak human beings like that, especially us males). Some of the edits this has been done to have been trivial ones that could have been better left alone or simply modified with some nice words in the the edit summary. The kick in the nuts that goes along with reverts has been exacerbated by uncivil nasties in the edit summaries. Let's knock it off. Skyway ( talk) 16:37, 6 April 2014 (UTC)
A citation was needed on the formula. How about: [1] Robin.Randall 1:03 9 July 2015 (UTC) — Preceding unsigned comment added by 128.107.163.58 ( talk)
Edit comment: Try this on for size. Made more clear that cable is frame of ref, "accelerate" no longer a tripping hazard. "Up/Down" is more general (not specific to Earth. The term "geosynchronous" is already specific to Earth, so trying to avoid saying Earth in the rest of the description is futile.
The more accurate way to describe this is that an object released from a space elevator below the synchronous orbit point will enter an elliptical orbit with the highest point being where it was released from the cable. An object released from a space elevator above the synchronous orbit point will enter an elliptical or hyperbolic orbit with the lowest point being where it was released from the cable.
Regrettably, the above sentence while general and accurate, is much less understandable. You're better off using earth-centered terminology (perigee, geosynchronous, ect.). Tarl.Neustaedter ( talk) 05:40, 14 May 2014 (UTC)
Take a break, Tarl. How much time did you spend on that bit of "nitpicking"? (eye roll) Skyway ( talk) 06:17, 14 May 2014 (UTC)
I see that some people discussing "What are the Constraints on Building a Tower to Space?" seem to think that the sheer mass of the cable makes it impossible.
Could someone please add to this article the total mass of space elevator? Preferably both the initial "seed cable" mass and the much larger "finished cable" mass?
Would it be relevant to compare that mass to the total mass of all the stuff people have already installed in geostationary orbit, including the stuff that has since been moved to a graveyard orbit? Would it be relevant to compare that mass to the total mass of a recent year's production of natural gas? (Natural gas is the raw feedstock for most recent nanotube production, right?) -- DavidCary ( talk) 08:42, 6 January 2013 (UTC)
I think finding out what confusions or misconceptions people have about space elevators then adjusting the article accordingly is a good thing. This article is the "go to" place where most people get all of what they know about Space Elevators. If there is a prevalent idea out there that SEs would be impossibly massive, we should make sure it's addressed in the article. We should probably cite something showing that reasonably anticipated designs require only a small number of large rocket launches (as DavidCary made a start on).
Skyway (
talk) 03:21, 8 January 2013 (UTC)
It seems to me it would be appropriate to discuss the need for two cables (or a wide web) to be built to efficiently allow an up climber and a down climber to pass each other. Two cables would lower the risk and allow maintenance on one while the other could be productive. The alternative would be to show how an up and down climber could pass at 300mph on one cable. 67.188.92.176 ( talk) 21:19, 01 June 2014 (UTC)
Hi there, I fixed an error here which someone has reverted.
https://en.wikipedia.org/?title=Space_elevator&oldid=612291048&diff=prev
I agree that it may well be going off topic - but the original text without my qualification in the next paragraph gives the false impression that you can return the materials of an asteroid back to Earth using a spinning tether. Instead, if it was, say, a million ton asteroid, you might be able to return one or two hundred tons this way - not worth the effort involved in building a space elevator. It might be worth doing for returning a sample.
So - what's the solution? Perhaps leave out the idea of using a space elevator on a spinning asteroid for mining?
But a space elevator could be used on a large enough asteroid say Ceres. The thing is you can't use it to mine a significant fraction of the mass of the asteroid or you will despin it completely. But you can use it for a very small scale mining operation of a few tons, or for a large scale mining operation on a very large asteroid.
Anyway don't think I'll attempt to edit again, but maybe someone esle can sort this out, so adding this note here with the information I found out.
I got confused by the statement originally - and actually wrote in one of my own articles that you can use a spinning tether for asteroid mining, without qualification, but couldn't remember where I read it and searching for the reference eventually traced it back ehre - and to the linked article, and then on careful reading of the linked article realized you can only extract a tiny fraction of the mass of an asteroid in this way - so wanted to correct the article so others reading it would not get the same false impression I got . Robert Walker ( talk) 00:17, 11 June 2014 (UTC)
Valid complaint. Check out the attempt to subdue "bulk" without adding too many words supporting what is a fairly minor mention. 100.0.101.252 ( talk) 16:59, 11 June 2014 (UTC)
Whoever wrote the Space Elevator article should update it so that it references William Forstchen's 2014 book, Pillar To The Sky. The book should be read and the imaginings of how this technology could be implemented should be summarized. — Preceding unsigned comment added by 24.2.86.57 ( talk) 02:40, 20 June 2014 (UTC)
The reason Yobot removes <small> tags from image descriptions: Error 66 - The description is already set to 94% in the stylesheet. This causes problems with people who have trouble reading small print. In other words, the fact that it may look nicer to you and I doesn't mean it's accessible to someone with vision problems. Tarl.Neustaedter ( talk) 14:58, 9 July 2014 (UTC)
I believe ksj.mit.edu is a reliable source and demonstrates a brief mention is due. -- Ronz ( talk) 15:13, 1 August 2014 (UTC
The ribbon thickness and material strength equations are labelled as original research. I have seen them on a website. I wish to remove the label. Have the equations occurred in a formal paper or textbook? Andrew Swallow ( talk) 04:42, 9 January 2013 (UTC)
user: Skyway, I assume you can bear the responsibility for maintaining a sign error in that section - not to mention other problems. Well - your problem, not mine, I was just trying to improve that encyclopedia. But, then, when Huns are on the loose, scholars can but hide away. Biem ( talk) 20:05, 21 November 2014 (UTC)
Now, since that integration is but plain calculus and beaten track, is there an objection to move the "section OR" flag down to the sentence "It turns out that between these two points, this quantity can be expressed simply" - in order to point more accurately to the point where it ceases to be beaten track and may indeed be somehow personal development (though neither false, nor reasearch level) ? Biem ( talk) 13:50, 5 December 2014 (UTC)
OK :
Biem ( talk) 19:57, 6 December 2014 (UTC)
OK, I think your objection (though per se legitimate) is out of purpose in this case :
Thus, as I see it,an integration of that differential equation cannot be considered as an original research, it is just in that case a redaction work needed to present to the layman reader facts already known (and used in the article), and understand why the initial equation (documented) relates to other facts presented in the article, and leads to a very strong constraint on the material used for the space elevator tether (which is important for the comprehension of the issue).
Biem ( talk) 22:54, 6 December 2014 (UTC)
Unless you have a stronger argument related to the "original research" problematic, I shall therefore move the "section OR" flag down to the sentence "It turns out that between these two points, this quantity can be expressed simply", and let you flag the equations with whatever "reference needed" you may wish to add. Biem ( talk) 23:15, 7 December 2014 (UTC)
Wikipedia articles must not contain original research. The phrase "original research" (OR) is used on Wikipedia to refer to material—such as facts, allegations, and ideas—for which no reliable, published sources exist. This includes any analysis or synthesis of published material that serves to reach or imply a conclusion not stated by the sources. To demonstrate that you are not adding OR, you must be able to cite reliable, published sources that are directly related to the topic of the article, and directly support the material being presented. (This policy of no original research does not apply to talk pages.)
The prohibition against OR means that all material added to articles must be attributable to a reliable published source, even if not actually attributed. [...]
Your reasoning is going the wrong way : "Published => Not OR" is not equivalent to "not published => OR", you are taking it for an equivalence which is a common mistake. But anyway, as stated above : * The basic differential equations are those published in the paper cited, The physics of the space elevator. They have already been referenced in the article, and cannot be considered as OR. Biem ( talk) 07:29, 8 December 2014 (UTC)
OK, if that equation is part of those published in the paper cited, The physics of the space elevator: is it acceptable to cite them as such, translate the "OR" flag and move forward to the next section?
Biem ( talk) 18:57, 8 December 2014 (UTC)
Guys, the offending uncited and dubious (and pedantic IMHO) text has been been tagged so for more than two years. Any of us would be completely justified in immediately removing it altogether. I am tempted to do just that. Then, according to
WP:burden, it could not be reinstated without the (now) required citations. But, I think removal would be harmful because that idealized cross section curve is indeed historically notable in the development of space elevator designs. I also think removal isn't really necessary because there are lots of refs out there for this. It's just a matter of investing time into going out and getting them.
To start with, it looks to me like that name="aravind" ref (PKASpace Elevators.pdf) could do the job of justifying removal of the larger OR tag. Having perused the ref, it looks pretty good for covering the "constant stress" postulate at least. Someone would have to look at it closer to see if it covers the "pedantic integration" and the resulting curve (though it probably does). I'll put that ref in to cover the integration and the resulting curve as well as "constant stress", then I'll remove the tag and see how it goes. I'd still like to see an additional discussion on the modern cross section shapes, but at least there is some wording saying that the given curve is "idealized", so that will have to do for now.
Skyway (
talk) 20:40, 8 December 2014 (UTC)
You're right. Citations are always better when they give specific pages, paragraphs, etc.. Citing the paper as a whole is more vague, but better than no citation I think. It's also a step, small or large, on the way to betterment. Other sources could be found and cited too. Anyone up for any of that? Until that better state is achieved, the current state (imperfect citing, no section tag) is probably better (less controversial too) than the previous state (no cites, section tag). Eh? Skyway ( talk) 04:04, 9 December 2014 (UTC)
Over the last few hours I've given that paper a closer look too and indeed it doesn't give our equations exactly. A good source should. I agree with Tarl there. One problem is that each source states the same idea or equation almost always somewhat differently than the others. Ultimately, the more equationeering done here, the harder to find exact duplicates in the sources, and making it especially hard to use more than one source. That's (yet) another argument for removing the "pedantic integration" and only mentioning 1) the "constant stress" starting point (easy multiple sources), and 2) the complicated resulting S(r) equation taken from one of the sources. That way we don't have to source "g=GM/r2" or any of the other intermediary pedantic bullshit -- just delete the middle garbage! :-) Still, I'd like to keep that imperfect source there for the time being (to stave off the section tag) while we find better sources and do some other rewording. Skyway ( talk) 07:25, 9 December 2014 (UTC)
Suggestion to replace it with the correct link, http://www.thetimes.co.uk/tto/news/world/article1967078.ece — Preceding unsigned comment added by Katacarbix ( talk • contribs) 16:36, 27 March 2015 (UTC)
A security point. If diamond nanothreads are used in the space elevator do NOT call them diamonds. Otherwise every burglar and mugger within a 1000 miles will try to finance his drug habit by stealing some and fencing it at the local jeweller. Calling it crystalline carbon will fool most of them. Andrew Swallow ( talk) 20:57, 3 April 2015 (UTC)
Anyone mind if I set up this talk page for automatic archiving (MiszaBot)? I'd just create archive_9, but this page gets long enough that it's probably worth automatically archiving discussions which haven't been active for over 30 days. Tarl.Neustaedter ( talk) 04:58, 16 March 2015 (UTC)
somehow by placing a rail around equator to atach it to in both ends — Preceding unsigned comment added by 181.128.21.174 ( talk) 11:16, 17 February 2015 (UTC)
This should be removed. Please link to research not wonder aloud. 2601:5:9380:6E:D955:EC7F:4858:8AAD ( talk) 05:49, 6 April 2015 (UTC)