Talk:Space elevator

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skyhook is a misnomer?[edit]

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)

Actually, a 'skyhook' is a fictional device that literally hooks onto the sky itself. Often used in humorous folk stories and jokes initiating apprentices at workplaces. In recent years the name has been used for real devices. Ashmoo (talk) 11:50, 24 February 2011 (UTC)
The name “Skyhook” to describe the structure of an object in orbit or near-orbit with a cable (of some sort) to the planet below is the proper name; Giuseppe COLOMBO, an Italian Mathematician and engineer, coined the term. A “space elevator” (the thing that goes up and down) is not requisite to the operation of a skyhook.Wikipedia- Best Source Of Information Since The Weekly World News. (talk) 01:56, 3 July 2011 (UTC)Andering J REDDSON

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 (talkcontribs) 21:35, 2 July 2010 (UTC)

Physics section[edit]

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)

This is not an article in a popular science magazine, it's supposed to be summarising the science according to the literature.Rememberway (talk) 15:05, 2 April 2011 (UTC)
The purpose of an encyclopedia is to be a reference work. You're supposed to be able to find a complete summary of the topic here. Those equations and the physics is really fundamental; not everything in the Wikipedia is easy; if you don't believe me, check out some of the maths articles ;-).Rememberway (talk) 15:05, 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)

We need equations about the cable area more than we need equations on the apparent gravity. If I find that there are no equations on this in the article I will revert to a version that has them again. But other than that if you can improve the article in any other way.Rememberway (talk) 19:38, 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)

With all respect, "tone-free" after "pedantic spewing by some 20-something male" (!?!), and I think the points made at WP:NOTOR need emphasising here (individual equations should not necessarily be citable nor transparent to lay-readers). I do agree the article is a bit of a mess yet, and appreciate your effort, but I also agree with Rememberway that it could never be an improvement to have no equations here. (Personally I think one problem is that certain equations are given excessive explanation in the text; it would be better to rely instead on better linking to other wiki articles for those readers who need the background foundations explained in detail.) If I recall correctly, Arthur C Clark's article (from the external links section) should suffice to demonstrate that the physics isn't original. Cesiumfrog (talk) 02:51, 6 April 2011 (UTC)
Okay, I take back the "... by 20-something males" comment. I was referring (only in my own mind apparently) to some studies I had heard about the demographics of WP editors, and to jokes about the aspergery-like proclivities of that population.
I don't actually advocate "no equations", it's just that equations without (good) explanation are very little communication at all. We technical people understand them (sometimes), but we must put ourselves in the minds of people who aren't inside our own minds. When we don't care about actually communicating, than what results looks a lot like mere showing off. Even E=Mc2 can't sit by itself. If equations must be included (ugh! :-) ), then really good explanation must surround them.
Skyway (talk) 02:25, 3 June 2011 (UTC)
There could be a section dedicated to the deeper understand (the physics at a physicist’s level), with the rest of the article dedicated to layman understanding. Equally, this section itself can be summarized, then linked to a full article (as is usually done in these cases). Wikipedia- Best Source Of Information Since The Weekly World News. (talk) 02:01, 3 July 2011 (UTC)Andering J REDDSON

Image error[edit]

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)

3 options: You can edit it yourself. You can show us some documentation for why it should be this way. You can explain it. Both terms are all over this article and I'm no expert on the stuff. The picture says "geosynchronous" so if someone thinks that's wrong we need to know why and find a better picture. I could easily edit the picture and re-upload it if I had a reasonable expectation not to mess up the science behind this page. Pär Larsson (talk) 11:50, 10 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)

Problems with the main (first) diagram.[edit]

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)

Fixed. 203.122.195.217 (talk) 03:18, 16 August 2012 (UTC)

Strength of materials comparisons[edit]

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)

This isn't such a ridiculous statement as you make it out to be. If we were to assume that the current, nascent, state of CNT production and technology were to be the technical limit, it would be akin to declaring that pearlite and martensite were the best you could possibly do with steel, and deciding you might as well not bother. The article does say that this is new technology, and that these are expected but not extant material candidates. siafu (talk) 23:31, 12 August 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)

That's the wrong question. We don't have the material yet, so technically of course that hasn't been conclusively examined. But if it were going to be a problem, we could simply increase the cross section sufficiently to support just adding an arbitrarily thick layer of shielding to eliminate it. Producing a material of very high strength on a macroscopic scale really is the one and only issue of importance here, everything else is ammenable to trivial work arounds. Cesiumfrog (talk) 03:39, 15 March 2012 (UTC)
I agree that getting the material strength-to-density in the first place is the primary concern, but I wouldn't say it's the wrong question. The answer to the question is "Yes". I would say it's been "adequately examined" for the current state of development. That is, practitioners know it is necessary to design for the environment and that that is one aspect of the environment that's been looked at (see Edwards Westing Phase Two). It's not expected to be too much of a problem. Like Cesiumfrog said, it looks amenable to "trivial work arounds" or as I would put it "routine design to given constraints" (or something like that). Skyway (talk) 17:37, 26 March 2012 (UTC)

Center of mass vs center of weight[edit]

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 (talkcontribs) 23:39, 12 August 2011 (UTC)

I was the one who reverted and believe this is a matter of properly formulating (what weights are being described). "Center of weight" is just not used in physics, but center of mass is a standard term. Materialscientist (talk) 23:47, 12 August 2011 (UTC)
I don't think it's the correct term in this instance. A much larger percentage of the cable mass will be above GEO, but if you look at the weight pulling down versus the weight pulling up it will be very close to 50/50. Should the article use "center of weight" if it's the correct term but also more confusing? — Preceding unsigned comment added by Nydoc001 (talkcontribs) 00:13, 13 August 2011 (UTC)
"Center of gravity" is a commonly used term in engineering, perhaps this is more illustrative of the reality. siafu (talk) 00:23, 13 August 2011 (UTC)
I think "center of gravity" would make sense here. If you think the mass below GEO providing "downward gravity" and the mass above GEO providing "upward gravity" then the gravitating sections of cable will be opposed with the center of gravity being slightly above GEO. — Preceding unsigned comment added by Nydoc001 (talkcontribs) 00:57, 13 August 2011 (UTC)
Ah, you mean to include the force direction. Center of gravity is indeed a common term. Materialscientist (talk) 01:02, 13 August 2011 (UTC)
Excellent! I'll make the change now then to say center of gravity. — Preceding unsigned comment added by Nydoc001 (talkcontribs) 01:09, 13 August 2011 (UTC)
By the way, the image at the top should say "Center of gravity for cable (above geostationary level)" instead of "Center of mass for system (above geostationary level)." I could edit the image to fix this, but I don't know how to upload it. Nydoc001 (talk) 01:17, 13 August 2011 (UTC)Nydoc001
No. This isn't a matter of the same term for different things, center of gravity and center of mass are different points. Unless you have a reference, I don't think it should be changed.- Sheer Incompetence (talk) Now with added dubiosity! 01:50, 13 August 2011 (UTC)
In fact, center of gravity isn't always a well defined point, whereas center of mass is easy to calculate.- Sheer Incompetence (talk) Now with added dubiosity! 01:50, 13 August 2011 (UTC)
They're only the same point if gravity is constant, but it's not because it's so big.- Sheer Incompetence (talk) Now with added dubiosity! 01:53, 13 August 2011 (UTC)
Well I'll try to find a reference for you. I'm sure I remember seeing it in either Bradley Edward's or Jerome Pearson's papers, but I know for a fact that we can't be talking about either the center of mass of the cable or the center of mass of the earth-cable system. Those are at different locations than GEO. Nydoc001 (talk) 01:59, 13 August 2011 (UTC)Nydoc001
I found some references:
Space Elevators - An Advanced Earth-Space Infrastructure for the New Millennium
Compiled by D.V. Smitherman, Jr.
Marshall Space Flight Center, Huntsville, Alabama, August 2000.
http://www.spaceelevator.com/docs/elevator.pdf
In this paper, Smitherman does say the GEO station is the center of gravity of the system:
"At the GEO transfer station (fig. 2(d)), passengers and cargo are transferred into the station or to outbound space transfer vehicles. This station is the center of gravity for the total system; consequently, large reels are illustrated to adjust the location of the station, tension of the structure, and the counterbalance mass."
However, Smitherman seems to use the terms "center of gravity" and "center of mass" interchangeably:
"A space elevator is a physical connection from the surface of the Earth to a geostationary Earth orbit (GEO) above the Earth ≈35,786 km in altitude. Its center of mass is at the geostationary point such that it has a 24-hr orbit and stays over the same point above the equator as the Earth rotates on its axis."
Dr. Bradley Edwards comments on the complications of gravity when altering the center of mass:
"A second fact that complicates our calculations is that as the cable is deployed different parts of it experience different gravitational acceleration. This changes our apparent mass distribution and if we want to maintain a geosynchronous orbit during deployment we must dramatically increase our orbital angular momentum. In our specific situation the geosynchronous orbit altitude for our center of mass depends on how much cable we have deployed."
The Space Elevator: Phase I Study
Bradley C. Edwards, Ph.D.
http://www.spaceelevator.com/docs/472Edwards.pdf
If you take a look at the wikipedia article for Center of gravity, there is a section about weighted average which states "Asimov (1988) writes that a body in the earth's gravitational field has a center of gravity that is lower than its center of mass, because its lower portion is more strongly influenced by the earth's gravity." This is exactly what's going on with the space elevator. The center of mass is closer to the counterweight, but the center of gravity is nearly at GEO because of earth's gravity.
As the article currently stands, it contains the terms "center of mass," "center of gravity," and "center of weight." I don't think it should use "center of weight" because it isn't a physics term. The only term that should be used when describing the point slightly above GEO is "center of gravity" because it is most accurate. Nydoc001 (talk) 04:15, 13 August 2011 (UTC)Nydoc001
No, it's actually, categorically, wrong. The centre of gravity is a long way below geo, since most of the gravity is quite near the earth, so the centre of gravity is near there (I've never done the maths on it, but it must be a few thousand kilometres up). The centre of mass is slightly above geo, as Bradley notes.- Sheer Incompetence (talk) Now with added dubiosity! 05:17, 13 August 2011 (UTC)
If you're thinking of the center of gravity of the earth-cable system, it would be almost exactly at the center of the earth. The final mass of Edward's ribbon, including the counterweight is 1500 tons and the mass of the earth is 6.585x10^21 tons so the cable and counterweight masses hardly make a difference. What makes sense to talk about are the centers of mass and gravity of just the cable. Only a quarter of the cable's length is below GEO. The other three quarters are above GEO. This puts the center of mass of the cable far, far above GEO, but because a body that is in a gravitational field has a center of gravity that is lower than it's center of mass, the center of gravity of the cable will be just above GEO. This is the balance point of forces pulling down and forces pulling up, so it's the center of gravity. Nydoc001 (talk) 05:46, 13 August 2011 (UTC)Nydoc001
If the "centre of mass" and "centre of weight" of the cable are at different locations then the article needs to say so. Particularly if the difference has to be allowed for during construction and for safe operation of the space elevator. Include definitions. Andrew Swallow (talk) 20:34, 15 August 2011 (UTC)
They would be at different locations. The balance point of upward forces and downward forces (you said "center of weight" but you could say "the elevator's center of gravity") by necessity needs to be slightly above GEO. The altitude of the center of mass will vary depending on how big the counterweight is. For example:
Assuming a ribbon taper ratio from base to GEO of 1.5 and the ribbon having sufficient length above GEO that it doesn't require a counterweight:
143,800 km - total length of ribbon
35,786 km - height at GEO
250.7 cm - final ribbon thickness at GEO
167.1 cm - final ribbon thickness at base and terminal point
0.002089 * 35786 = 74.756954 km^2 - surface area of ribbon below GEO
0.002089 * 108014 = 225.641246 km^2 - surface area of ribbon above GEO
This means that a cable with maximum possible length would have approximately 25% of it's mass below GEO and 75% of it's mass above GEO. Therefore the maximum possible altitude for the center of mass should be somewhere around 70,000 km.
Blaise Gassend has a page that talks about the center of mass for space elevators: http://gassend.net/spaceelevator/center-of-mass/index.html
Nydoc001 (talk) 05:18, 16 August 2011 (UTC)Nydoc001


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)

The gravity of Earth is about 100 times stronger at sea level than at altitude 54,000 kilometers (60,000 km from the center of the earth), so it would take more mass beyond GEO altitude to counter balance the mass below GEO altitude.
There is a balancing point. The balancing point is the point for which the total force on the mass above that point (mass times (centripetal acceleration - gravitational acceleration)) is balanced by (equal to) the total force on the mass below that point (mass times (gravitational acceleration - centripetal acceleration)). The balancing point should be slightly above GEO so you could have a natural 20 ton upward force and not pull it out of the sky when you put a 15 ton climber on it. Could you call this point "the cable's center of gravity" or is there really no common physics term for this point?
The only reference I could find talking about this is Blaise Gassend's Paper which is already listed in the article's references: http://gassend.net/spaceelevator/center-of-mass/index.htmlNydoc001 (talk) 21:01, 18 August 2011 (UTC)Nydoc001

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)

If you're going for accuracy, you could say "center of gravity adjusted for centripetal acceleration" (that's a mouthful! CGACA?). I don't think "center of mass" is accurate, but would "center of balance" cause less confusion?Nydoc001 (talk) 21:21, 19 August 2011 (UTC)Nydoc001
This might be a better explanation of why the balance point is not the center of mass:
The "center of balance" is the point at which the net force acting on the elevator mass below that point is equaled by the net force acting on the elevator mass above that point.
Since we want the whole elevator to have a 20 ton pull-down margin, we put the center of balance slightly above GEO (an elevator having a net downward force would have it's center of balance below GEO).
But the center of mass isn't anywhere near GEO! This is because gravity increases faster exponentially as you go downward than does centripetal acceleration as you go upward. A given elevator mass below GEO will have a stronger net downward force than the net upward force acting on an equivalent elevator mass above GEO. You'll have to compensate for gravity by placing a much larger cable mass above GEO, in order to provide yourself with more centripetal acceleration. This is why you end up with your center of mass being perhaps 10,000 km above the center of balance.Nydoc001 (talk) 03:12, 20 August 2011 (UTC)Nydoc001


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)


Center of what?  :-)[edit]

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)

When anchored, the system has to include either the Earth (which it is anchored to) or the force being provided by the Earth extending out of the control volume both as a body force (gravity) and as a point force (tension), otherwise it doesn't really gain much in terms of it's usefulness as an arbitrarily defined system. siafu (talk) 01:14, 19 August 2011 (UTC)
You should consider Earth's gravitational force when locating the elevator's center of gravity, but you wouldn't need to include the Earth's mass into the system when locating the center of mass. Typical skyscrapers have a center of mass (very important when planning for earthquakes) but the Earth's mass isn't included to find a skyscraper's center of mass. The CG and CM of a skyscraper are very close together, but a space elevator is so tall that these points would be very far apart. For an elevator having the longest possible tether and smallest possible counterweight they could be as far apart as 36,000 km. Even for shorter tethers they will still be thousands of kilometers apart.Nydoc001 (talk) 01:27, 19 August 2011 (UTC)Nydoc001

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)

Any spacecraft that attached itself to the elevator would become part of the system, but if they attach at GEO altitude they will be in free fall with zero weight and so not add any additional force or tension to the tether. You could theoretically add infinite mass at GEO altitude without altering the tether's profile.Nydoc001 (talk) 20:07, 19 August 2011 (UTC)Nydoc001
Were I not an astrodynamicist, I would not feel compelled to object, but alas I must point out that a large mass at GEO would be problematic due to its gravitational effects, as well as the more serious effects on the structure's overall oscillatory behavior. siafu (talk) 20:51, 19 August 2011 (UTC)
You have a very valid point. Infinite point mass would be a problem for the universe as a whole. But I'm sure you could get away with attaching something with mass equal to a few dozen times the ISS at a space elevator's GEO without causing too adverse an effect. I think the change in oscillatory behavior would be the most noticeable effect. — Preceding unsigned comment added by Nydoc001 (talkcontribs) 21:05, 19 August 2011 (UTC)Nydoc001


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)

Little mistype?[edit]

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)

In this case 'above' goes with 'safe', and means the radiation is dangerous. Andrew Swallow (talk) 18:14, 29 March 2012 (UTC)

Some phrases in the "21st century" section are in a different font and without spaces. For example "which featured US500,000⁢a⁢w⁢a⁢r⁢d⁢s⁢f⁢o⁢r⁢e⁢a⁢c⁢h⁢o⁢f⁢t⁢h⁢e⁢t⁢w⁢o⁢c⁢o⁢m⁢p⁢e⁢t⁢i⁢t⁢i⁢o⁢n⁢s,⁢(U⁢S1,000,000 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)

Hmmm... I checked and my browser shows it looking normal. I have Firefox 10. Skyway (talk) 03:19, 22 May 2012 (UTC)

Effect of space elevator on earth's orbit[edit]

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)

The effect on Earth would be negligibly small, since a space elevator's mass is tiny compared to Earth's mass. --Roentgenium111 (talk) 17:07, 13 September 2012 (UTC)

Effect of space elevator on counterweight's orbit[edit]

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)

constraints on construction[edit]

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)

As with many discussions on this talk page, this is all either original research or original synthesis. siafu (talk) 14:44, 6 January 2013 (UTC)
I went ahead and added the masses of a few space elevator designs to this article, with references.
Later I see that siafu seems to be warning me that "this" (?) is against policy. Oops. Am I misunderstanding the policy, or misunderstanding siafu, or (most likely) both? --DavidCary (talk) 18:52, 7 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)

Original research equations[edit]

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)

Personally, I wish the equations would go away (I see them as pedantic). But, I know there are other opinions out there. The other trouble with them (besides "pedantic") is they really aren't up to date. Before Edwards-Westling (Phase II) (~2002), the level of detail in people's thinking regarding taper was only at the level of "Gosh, how do we taper it to most efficiently hold itself up?" Those idealized equations did apply before 2002. Since then, with the work of Edwards (~2002) and more recently the publications of ISEC (~2012), the bar has been moved. Nowadays we consider thickening at space-junk altitudes, load concentrations as they vary with the distribution of climbers, distribution of non-structural mass, etc. That equal stress idea is an important principle yes, and it should be mentioned, but it's not so important these days to go into its excruciating details IMHO.
I haven't done a complete search, but my expectation is that those equations (similar to as they appear now) would be found in pre-2002 sources (which are outdated), or "unreliable" post-2002 sources (because they regurgitate pre-2002 sources), or just somebody's intellectual exercise they published on WP as OR. What we're really trying to do is describe taper and constraints on the taper design (right?). I would trust descriptions of taper from Edwards Phase II, or the ISEC stuff. Both refs are already in the reflist. It would be a matter of reviewing them to find the good stuff in them. Skyway (talk) 09:25, 10 January 2013 (UTC)
Will someone please publish the equations in a peer reviewed academic paper or text book so we can reference them. Andrew Swallow (talk) 23:35, 18 November 2014 (UTC)
The basic equations are those published in the paper cited, The physics of the space elevator. They have already been referenced in the article, just before the point where they are introduced...
The calculus and algebra for the development is quite straightforward, and do not qualify as "research" (BTW I corrected a forgotten minus sign). There certainly has been some intellectual work to present these sections, but it is mostly (scientific) redaction, definitely not research. It's the kind of dimensional analysis that Arthur C. Clarke has used decades ago, yielding the same results (see note 33, ,960 km "escape length").
To me, some redaction work is OK as long as it enables the reader to understand some point presented in the article, especially when that point is counter-intuitive, and the explanation is basic physics. A very crucial point, for instance, is that the taper varies exponentially with the free breaking length. I have seen in the discussions above someone saying that a linear growth would do the trick - that is dead wrong, and you can't understand why as long as you've not looked at the basic equation. Another crucial point is that the rotational speed has but a second-order influence in the feasibility of the elevator : I have seen discussions about the Moon elevator saying that since the Moon has no rotation to speak of, no cable could be anchored, since it is the centrifugal force that holds it upward - Once again, dead wrong, but to understand that you need to see the taper expressed with that "x" formula, which shows that the main factors are the ground gravity and the planet radius - not that much the rotational speed.
I don't really care these sections being flagged as "OR", which was apparently the point of this small edition war, though I find it excessive. But they are crucial to understand some developments of the article, and they needed some rephrasing and corrections (which was the purpose of my intervention).
Biem (talk) 06:36, 19 November 2014 (UTC)
Then you win the edit war by adding <ref name="aravind"/> at the end of the paragraphs and can celibate by removing the OR notice Andrew Swallow (talk) 09:29, 19 November 2014 (UTC)
Not so fast. Finding a fair reference is only one factor in includability, and the section has many includability problems. For one thing by the way, that .pdf cited by Biem is not reliable if it doesn't account for point masses, thickening at high space junk altitudes, etc. There's also a big question of undue weight (WP:undue) given to arcane details like this. It's all very sweet to personally get down and dig into idealized equations, and then to want to show the world, but includability in a Wikipedia article asks for more than that. The section as-is is questionable on includability because it's OR, not very communicative, etc.. Biem's self-described "improvements" look more like common pedanticism (forgive me) and only make the section's existing WP:OR, WP:undue, and pedanticism problems worse. I support their rejection for the time being while the pile can be sorted out. Skyway (talk) 21:13, 19 November 2014 (UTC)
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) 20:03, 21 November 2014 (UTC)
Putting aside the nutty "I'm a would-be hero" melodrama, I imagine you do know that there's much more to it than that. If one hides a legitimate correction in a haystack of chaff and then acts bewildered that no one wants to sort through the whole stack to find the single fleck of any value, well I think that's being unrealistic. Skyway (talk) 19:59, 22 November 2014 (UTC)

Safety : Earth Weather[edit]

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)

My read is that terrestrial weather would be effectively irrelevant - forces are orders of magnitude smaller than the ones needed to simply support itself, and passing through the Van Allen belts means higher electrical charges than you'd get from terrestrial storm clouds. As for thrusters, moving cargo up and down the elevator will cause changes in angular momentum, moving the geosync point forwards and back. This would presumably be adjusted by simply pulling in or letting out some of the counterweight to shift the center of gravity. Tarl.Neustaedter (talk) 19:13, 7 September 2013 (UTC)

Climbers section[edit]

The changes which have been whip-sawing back and forth in the Climbers section are getting tiresome. The 66% is simply wrong (it's unreferenced, and my back-of-the-envelope calculations come up with a different height, which isn't a magic number), but the other changes which keep being put in are even worse. If nobody comes up with references for that section, I'm going to delete the entire chunk of text. Tarl.Neustaedter (talk) 02:27, 15 December 2013 (UTC)

I should add - it's absurd to talk about achieving low-earth orbit from a geocentric space elevator. Any object released from a beanstalk (to use the other common name) will be co-planar with the cable and eventually (probably in less than two orbits) impact the structure, destroying it. This is one reason we need references, so we don't have arguments like this - someone writing for a reliable source will have either addressed this issue or responses to it will have been made and we can quote those too. This is very much a case where we should avoid original research. Tarl.Neustaedter (talk) 02:33, 15 December 2013 (UTC)
I already reverted the edits of IP68. We're back where we started, I think were safe now from those efforts by IP68 (I think they really were "good faith", just muddled, digressive, etc.). It's not necessary to delete entire chunks of text IMHO. I think a simple "citation needed" tag would be a less drastic solution for the time being. In the process of mass-reverting IP68's stuff, that recently-added tag got wiped out too. I let it stay removed because I was lazy and I honestly would have preferred it without the tag. But, if it has to be there that's better than wholesale removal :-).
Check your calculation again on the release from 66%. If something is released from that height, it's perigee will be just above the atmosphere. As far as a ref goes, there's one here (http://www.endlessskyway.com/2010/05/space-elevator-to-low-orbit.html). I'd cite it, but I'm not allowed because I wrote it. If you think it's reliable or if others do, it might be okay to cite it I suppose. I'm definitely not looking for links to my essay there, it's been there for three years and I haven't mentioned here until now. I only mention it now because I'm hoping to ease your urge to delete for want of a citation :-). There's also a crude Javascript simulator there to play with real time orbital mechanics and releases from any level of an Earth or Lunar Space Elevator. Again, I only mention it because it might be useful or fun for you to play with, not to promote it.
Also, as far as getting to LEO from a SE, that link discusses how to do it. Basically drop from a height slightly less than 66% so that the perigee dips slightly into the atmosphere for aerobraking. It might take a number of orbits with draggy perigees to gradually knock the apogee from "66%" down to about 350 km. Then at the 350 km apogee a very small delta-V is needed to bring the perigee up so it doesn't dip into the atmosphere anymore. No one is saying it can be done without any delta-V. It's just that the delta-V needed is extremely small compared to the 35,000 fps needed to get to LEO from the surface with a rocket. The delta-V needed to lift the perigee out of the atmosphere is somewhat smaller than a normal de-orbit retro burn from LEO (which is only about 300 fps). In fact, it's the very same thing in concept except it's backwards, the "negative" of a de-orbit burn.
Skyway (talk) 22:07, 15 December 2013 (UTC)
I found another ref for "66%": http://gassend.net/spaceelevator/falling-climbers/index.html
The maximum altitude shown in the graph shows the altitude at which the dropped object does not intersect the Earth. From what I can see, this ref considers intersection with the surface, ignoring the atmosphere. That would put it at a lower end of "about 66%, but it still supports "about 66%" for a perigee just at the top of the atmosphere.
Gassend's work on this site is considered to be very reliable.
Skyway (talk) 01:13, 16 December 2013 (UTC)
Regarding hitting the cable. Yes, this subject is undiscussed (as I recall) in the article and it's probably a good (notable) candidate for inclusion. To summarize it, in a two dimensional world, most free-flying satellites would hit the cable in very short order. In a three dimensional operational world, factors conspire to cause them to miss:
1) "Big sky theory" -- The cable is thin, satellites are small, space is big.
2) Active management -- Collision avoidance is a major factor in SE design and operation. Most designs are able to maneuver out of the way of approaching satellites. Satellites themselves are able to maneuver.
3) Inclination -- Most satellites would have a thrusting phase after release to put them at the desired inclination. This puts them in the 3D world where the frequency of close approach is drastically reduced.
4) The cable itself oscillates like an upside down plumb bob and like a guitar string, meaning that even w/o post release thrusting the satellite would have a small inclination. The cable would also oscillate to somewhere else the next time around. This gives a statistical "fuzz" to how close the encounter would be each time.
Skyway (talk) 01:56, 16 December 2013 (UTC)

Please curb your enthusiasm deleting section about equilibrium at geostatioanry orbit. Everything there is correct, factual, and true. This is Physics 101. — Preceding unsigned comment added by 68.228.67.228 (talk) 21:23, 17 December 2013 (UTC)

Two things. First, it's unreferenced. For inclusion into Wikipedia, being accurate isn't sufficient - you have to cite a Reliable Source saying so. This article has a real problem of Original Research, don't make it worse. Second, it's not relevant. That the geostationary point on a beanstalk is an equilibrium point is (as you point out) obvious, and thus unnecessary. It's simply not relevant, it's an unimportant description. Tarl.Neustaedter (talk) 21:41, 17 December 2013 (UTC)
It's not as obvious as it seems; the scenario described in the text being inserted by the IP relies on a number of unrealistic assumptions, e.g. unrestricted or frictionless vertical motion, in order to be a valid conclusion. Given a small push in either vertical direction, the climber's natural inclination would be to follow a similar (to GEO) orbit per Hill's Equations, and only its constraint to the cable would prevent that. The harder the push, the more elliptic the natural resulting orbit. This is again why OR is so dangerous. siafu (talk) 19:59, 18 December 2013 (UTC)
IP68,
Some of it may be factual and true, but it was and still is so unclearly expressed that we (well, I) couldn't figure out at all what you meant. The words appeared as gibberish regardless of what actual correct Physics 101 ideas you may have in your mind. The adversarial relationship established early on signaled that hand-holding you to figure out what you were trying to say would be a lot of work and would very likely be unfruitful. Skyway (talk) 07:04, 18 December 2013 (UTC)
When converting 2/3 to decimal allow for the error bounds. Mathematically 2/3 may equal 66.6667 but the figures may only be accurate to 3 significant figures, giving 66.7 . The references actually gave the height, which someone removed. Andrew Swallow (talk) 12:57, 18 December 2013 (UTC)
Andrew, Tarl, I think we've got a bigger problem on our hands than refining the way we express that level. Now blocked, it looks like the former IP68 is now IP hopping and making the same changes. I don't recommend semi-protection quite yet unless it has a hard and fast expiration. (Too many other permanently semi-protected articles are now moribund without the efforts of IPs, all with the only very thinly supported justification of "persistent vandalism") This guy is offended and it looks like he's determined. Does anyone know a next step other than semi-protection? Skyway (talk) 17:02, 18 December 2013 (UTC)
I don't think this is the same person - One IP is in California, the other in New York. Just deal with it the way it is, and please, everyone start paying attention to WP:RS and WP:OR. Tarl.Neustaedter (talk) 18:42, 18 December 2013 (UTC)
Yeah, it could be more than one person. I checked the locations too. Still, it's not too hard to proxy around the country by a number of means, such as using friends' computers with remote desktop software. It's hard to say. Skyway (talk) 18:55, 18 December 2013 (UTC)

Possible GEO stability problem[edit]

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)

elevator on pole[edit]

I was reading the article and something popped into my mind. Probably other people already thought of it, but i would like to know if it's a good idea or not.

If you place the elevator on the pole, and let it rotate 1 revolution per day, in the same direction as the earth rotation, you already need a considerable lower elevator. You need an additional 6000 km since you are connected to the pole instead of the equator, but you save 27000 km because the new stationary orbit is 4 times lower due to the rotating and thus increased centrifugal force. (86.93.56.137 (talk) 10:55, 16 February 2014 (UTC))

Where is the pole? If the pole is at the North or South Pole something like that may work but will require enormous amounts of energy to move the entire elevator. Outside of about the Arctic and Antarctic Circles the elevator will crash into the Earth. Andrew Swallow (talk) 13:02, 16 February 2014 (UTC)

Yes, it must be the north or South Pole. The amount of energy needed is not that much. Only overcoming friction. The rotational kinetic energy is always there, just like the international space station. It has the kinetic energy but is not lessening it. 77.168.45.146 (talk) 13:20, 16 February 2014 (UTC) Sorry I see my ip 77.168.45.146 (talk) 14:25, 16 February 2014 (UTC) is changed since I'm now on my smartphone.

Do you have a citation? Your description defies rotational dynamics as I understand it. Where does that figure of 27000 km come from? Tarl.Neustaedter (talk) 04:13, 17 February 2014 (UTC)
F=rw^2 if w is halved then r quadruples. therefor radius goes from 36 Mm to 9 Mm. Thats how i got to the 27 Mm. Anyways it is a lot easier to just build a 100km tower since then you're already in space (according to definition) 194.105.120.70 (talk) 15:22, 18 February 2014 (UTC)
Do you have a citation? As best I can tell, this is a complete misunderstanding of orbital and rotational dynamics. Tarl.Neustaedter (talk) 20:48, 18 February 2014 (UTC)
What orbit is it in? Midgley (talk) 19:06, 18 February 2014 (UTC)


There would be no way to transfer angular momentum back and forth between Earth and the climbers. That's the key thing that separates a space elevator from all those other cutesy little space tethers (rotorvators, skyhooks, whatever). Off-equator anchor points would conceptually work, but only in a small range about the equator (+/-10 degrees or so). The vibration dynamics are much more complicated too. The other issue with a polar anchor point is that the cable would run horizontal to the ground for many hundreds of miles, it might not even be lifted off the ground for many degrees away from the pole.

Off-equator anchor points have been discussed in the literature, but more as a novelty. I don't think it's important enough to include except for a small mention of the possibility of moderate off-equator anchor points. An anchor point at the pole should not be mentioned IMHO. It would be a distraction.

The moon could handle larger latitudes for the anchor point because the elevator is held up not by centrifugal (pseudo)force as for an Earth elevator, but with the center of mass being well on the other side of L1. This could potentially be a notable mention.

Skyway (talk) 07:23, 21 February 2014 (UTC)

Please add nothing of the above speculations without a reliable source discussing it. There are so many things wrong in the above conversations I don't even know where to start. Tarl.Neustaedter (talk) 19:03, 21 February 2014 (UTC)

Placed over the pole, either north or south, the payload will gain absolutely NOTHING from the earth rotation, because the effective radius of rotation there is ZERO....so how can it be advantageous over equatorial placement where radis of rotation is 4000 miles just standing on the ground? — Preceding unsigned comment added by 68.228.67.228 (talk) 04:58, 26 February 2014 (UTC)

The pole is a rival to the equator. All the rotation has to be provided by an engine. Countries may have access to one of the poles but not the equator. Andrew Swallow (talk) 05:58, 26 February 2014 (UTC)

New report[edit]

..available here LeadSongDog come howl! 16:58, 26 February 2014 (UTC)

Cool reference, thanks. Formal title "Space Elevators: An Assessment of the Technological Feasibility and the Way Forward". I would suggest to other editors that when citing from this report, please use section numbers, since the page numbers are probably going to change as formatting errors in the document are fixed (e.g., equation 6.82 on page 172 is almost unreadable, so needs a fix - and that will probably change the length of that page moving text around). Tarl.Neustaedter (talk) 18:18, 26 February 2014 (UTC)

The problem with fast reverts[edit]

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)

Apparent gravitational field[edit]

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)

Oh, and may I suggest that nitpicking wording on obscure cases is not the most productive use of editor's time? Wordsmithing and re-wordsmithing the same paragraph over and over just leads to edit wars. Tarl.Neustaedter (talk) 05:42, 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)

Attempt to fix error in description of spining asteroid reverted[edit]

Hi there, I fixed an error here which someone has reverted.

https://en.wikipedia.org/w/index.php?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)

needs updating[edit]

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)

There are many science fiction novels with references to space elevators, no need to add anything to this article about a more recent novel. Tarl.Neustaedter (talk) 04:17, 20 June 2014 (UTC)
Agree. (with Tarlneustaedter) 100.0.101.252 (talk) 18:30, 20 June 2014 (UTC)

Yobot errors[edit]

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)

Okey Dokey. Skyway (talk) 23:42, 10 July 2014 (UTC)

Space shaft[edit]

I believe ksj.mit.edu is a reliable source and demonstrates a brief mention is due. --Ronz (talk) 15:13, 1 August 2014 (UTC

Ksj.mit.edu being a reliable source does not make SpaceShaft noteworthy for inclusion. The ksj.mit.edu article only tells the story as told by the primary source—the head or spokesperson of the SpaceShaft team. SpaceShaft itself is patent pending, and other than its public presentation, its claims has not been validated or scrutinised by any expert or professional body—WP:FRINGE. Thank you. —JOHNMOORofMOORLAND (talk) 22:55, 1 August 2014 (UTC)
I'm not sure I understand. Are you saying it is not an independent source? --Ronz (talk) 23:09, 1 August 2014 (UTC)
It looks like he's doing this to make a point after his own edit was backed out. I suggested WP:POINT, he riposted with WP:AGF. Tarl.Neustaedter (talk) 00:13, 2 August 2014 (UTC)
Let's try to focus on content here please. --Ronz (talk) 02:04, 2 August 2014 (UTC)

Bradley C. Edwards nominated for deletion[edit]

Bradley C. Edwards was first prodded without discussion on this page, the article is now on Wikipedia:Articles for deletion/Bradley C. Edwards, please express your opinion.Mion (talk) 22:43, 18 August 2014 (UTC)

Obstruction to any correction by Skyway[edit]

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)

I dimly recall there was a sign error (or something small) some time ago that someone corrected that wasn't an error and so it was corrected back. Yours might be the same, or it might not be. Can you point it out here? Skyway (talk) 19:34, 22 November 2014 (UTC)
The integration of
dS/S =  \rho/\sigma \cdot ( G \cdot M/r^2 - \omega^2 \cdot r ) \cdot dr
is incorrect, it should yield
\Delta\left[ \ln (S)\right]{}_{r_1}^{r_0}  = -\rho/\sigma \cdot \Delta\left[ G \cdot M/r + \omega^2 \cdot r^2/2 \right]{}_{r_1}^{r_0}
(with a minus sign) and should actually be written from ground (r_0) to geostationary (r_1), not the other way around (though the result is of course the same) :
\Delta\left[ \ln (S)\right]{}_{r_0}^{r_1}  = -\rho/\sigma \cdot \Delta\left[ G \cdot M/r + \omega^2 \cdot r^2/2 \right]{}_{r_0}^{r_1}
I hope this kind of elementary calculus can be corrected without being accused of unpublished research work...
Biem (talk) 15:07, 27 November 2014 (UTC)
So make the change and see what happens. I'd suggest making a single change in a single edit with a straightforward AGF edit summary like "Corrected sign error in equation (integral of dr/r^2 is *negative* 1/r). See talk page.". You'll either get complaints, or refinements, or reversion, or you'll get completely ignored. Getting ignored means the peanut gallery looked it over and didn't have enough of a problem to complain or anything else -- and that's pretty high praise here in WP! It's a good idea to make just the one (presumed) correction. The more changes one makes in a single edit, or in multiple edits in a short period of time, or the greater the "snoot content" in edit summaries -- then the more opportunity for consternation in the peanut gallery, the less likely any of the edits will be accepted happily (regardless of merit). Skyway (talk) 09:16, 28 November 2014 (UTC)
I've just re-read the above and I want to assure you that I was sincere, I wasn't trying to "challenge" you or dare you. I just wanted to give you the opportunity to make the correction you found, which if done by itself w/o other changes, would probably result in a more rewarding experience for you. I reviewed the math too and I think you are probably correct with regard to what should follow from that initial postulate of constant-stress. I just (personally) think the constant-stress idea is an outmoded one given modern (post Edwards) thinking. I also think that math details are generally off topic and distracting. I would try to improve/correct way the math is stated, but since I think the postulate is outmoded anyway, for me that would be like "putting lipstick on a pig" - so I've avoided it. But, if you want to make the math correction, you should I think. Skyway (talk) 18:48, 4 December 2014 (UTC)
Math detail is important in that case, as stated above, and even if a strictly constant-stress is outmoded it still is relevant for a dimentional analysis (what is feasable or not). And scientific readers may be interested in that.

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)

The problem is that the original differential equation is unsourced and presumably original research. If you can find somewhere that's published and reference it, then we can move the section OR flag. Tarl.Neustaedter (talk) 21:52, 5 December 2014 (UTC)
Right. It's the premise of constant stress that's the main unsourced "OR" part. It would probably be easy to find a ref, but reliability is the key thing here. Any ref that says "constant stress" is unreliable (!) IMHO as outdated and/or naive. The problem is that, since Edwards, there are more requirements on cable design than just the need to hold itself up. That's my issue. "Constant stress" is dubious in the modern age, yet many seem to like to focus on it (and then "digress pedantic" about the integration :-) ). Some time ago, some qualifiers were added to skirt the issue ("For such an idealized design without climbers attached..."). "Constant stress" is a start, but a better description would mention it and it's resulting cross section curve fairly briefly (no intermediate math), then focus on the variations on that in modern more fully fleshed out designs. By the way, the Edwards Phase 2 report is a great ref for that, ISEC might also have some even more recent papers. Skyway (talk) 04:54, 6 December 2014 (UTC)

OK :

  • The differential equation in itself definitely is not original research, since it is the equation that (for instance) yields the result given by Arthur C. Clarke in 1979.
  • I understand that the hypothesis "constant stress" is not the reference one at present (which would need to be explicated in the article, that is not my problem).
  • Would it be acceptable to mention somehow that "constant stress is a start" - which is the main point in this section, if "constant stress" cannot be achievable there is no way a space elevator can be realized. Of course, if sufficient material is available, other designs may be realized, but this is not the point discussed here.

Biem (talk) 19:57, 6 December 2014 (UTC)

That equation is still original research, unless you can find a reference where someone has published and discussed it. Whether someone else has derived it or not isn't the issue - it's whether we can reference a reliable source describing it. You may think it's trivially derivable, but Wikipedia is a tertiary source - the articles here are supposed to be no more than summaries and pointers to articles published elsewhere. If you have something interesting to say, this isn't the place to say it - this is only the place to point out where something else has published something interesting. Tarl.Neustaedter (talk) 21:15, 6 December 2014 (UTC)

OK, I think your objection (though per se legitimate) is out of purpose in this case :

  • 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.
  • The integration of these equation is a trivial calculus exercise (and is verified by Arthur C. Clarke statement of the escape length needed, which is quoted in the article).
  • The policy Wikipedia:No original research that you point out states that "The phrase "original research" (OR) is used on Wikipedia to refer to [...] any analysis or synthesis of published material that serves to reach or imply a conclusion not stated by the sources." This is not the case here, since the result of the integration of that differential equation is common knowledge, and may be found in various sources (including the previous one authored by Arthur C. Clarke).
  • On the other hand, that integration is needed in order to wikipedia:Verify the assertions of "4,960 km escape length" (calculated by Arthur C. Clarke in 1979), quoted on note 31. Verifiability is not just an "accepted standard" on Wikipedia, it is a Wikipedia:Core content policies : we are bound to verify the assertions found in the articles.

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)

If you find those equations published elsewhere, then cite them. Adding citations is what this article needs. In essence, every sentence and every equation should have a citation (don't just say "it's somewhere in that 1000-page PDF". Specify page/section number). Then you can move the OR tag.
The key here is that Wikipedia articles should be maintainable by a librarian who does not have expertise in the subject matter. Being able to follow references and differentiate between reliable and unreliable sources should be sufficient. Saying "it's a trivial exercise" is not sufficient - if you can't find it published anywhere, either it's not as trivial as you say, or it's not interesting enough for anyone to write down. The key again, this isn't the place for you to write something interesting - it's the place for you to point out where someone else has published something interesting and provide enough of a summary that it can be found. Tarl.Neustaedter (talk) 23:18, 6 December 2014 (UTC)
Tarl.Neustaedter, You seem to be badly mixing the problematics.
  • The policy we were refering to is that of Wikipedia:No original research - My point is that this passage is definitely not original research (see above, no need to repeat myself). In that context : The "section OR" is intended to flag original research as defined, and is therefore inappropriate, when the statement cannot be qualified as OR. It must therefore be moved or suppressed.
  • Your point seems to be that some assertion laks citation. This may be the case, but this is not my point (and, basically, I don't care). If an assertion laks citation, just add the "reference needed" flag to it, but it is not per se a OR problem. Please do not use a "cite" policy to discuss a "OR" prohibition - cases are different.
Biem (talk) 23:15, 7 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)

Maybe we're not talking about the same text. Where is the citation for:
\sigma \cdot dS = g \cdot \rho \cdot S \cdot dr
If you can find a reference which describes the entire group of equations, then you can reference that. Otherwise, you need to put a citation on each equation before you can move away the section original research flag. That flag cannot move away until we can track down these equations to a reference which someone not expert in this subject matter is able to verify. Tarl.Neustaedter (talk) 23:37, 7 December 2014 (UTC)
Further, let me quote from WP:OR:

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. [...]

Until that equation can be attributed to something, it is OR as above. The fact that you can conclude that someone else must have come up with this sometime in the past doesn't suffice - you have to show where it's been published. Tarl.Neustaedter (talk) 23:49, 7 December 2014 (UTC)

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)

The problem is that nobody knows it isn't OR until they see it in the reference. If it is hard to find in a reference, the OR tag may stay simply for the practical reason of verifiability. Adding citation needed tags could be done, as well, but the section tag usually stays until the issues are at least mostly resolved in that section. —PC-XT+ 08:12, 8 December 2014 (UTC)
I strongly disagree with that formulation.
A lot of people can read the equations, and verify them - engineers, physics majoring university fellows, and so on ; and any one of them can verify that the equation is a basic one, that it has obviously been used by quite a number of authors, including Arthur C. Clarke in his address on the space elevator. This, in itself, shows that it can't be WP:OR. Now, of course, the layman-level-internet-reader may not understand why the equation is basically correct and not a magic formula (As it would appear to my daughter, I'm afraid, which is not a scientist), but that is not the point: your claim that "nobody knows it isn't OR" is blatantly false. The problem is not for anybody to see by itself whether it's OR or not, the problem is to trust the Internet users that go through the equations and assert that it is basically correct.
As far as wikipedia:verifiability is concerned, we have all we need. It's OK, there is no problem.

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)

I did not mean nobody to be taken literally as no person. I was referring to readers who could not determine it for themselves. There are many who could determine it, but they are not cited, so nobody else knows it is not OR. Apologies for the confusion. I didn't mean to offend you or suggest that the formulas are actually OR. —PC-XT+ 02:47, 9 December 2014 (UTC)
I have formally challenged three of those equations, with the addition of {{citation needed}} tags in the article. Let's simply see if someone wants to supply citations to support those assertions over the next few weeks. Cheers. N2e (talk) 20:18, 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)

Which equations in Aravind are you citing? There are only 15 equations in that paper, it shouldn't be difficult to specify which equation you say is being referenced. Tarl.Neustaedter (talk) 22:45, 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)

The differential equation is n°6 and its integration is n°7. Biem (talk) 05:15, 9 December 2014 (UTC)
Claiming that is the same equation presented in the Wikipedia article is a long stretch. The article should be fixed up to present the equation as cited, and then describe whatever "obvious" transformation produces the simplified version used in the Wikipedia article. Again, present it in such a way that it can be maintained - so when an argument arises (as a few weeks ago) about wrong variables or wrong order, it can be sanity checked by an editor not expert in the material. (Wikipedia articles need to be written by people expert in the material but left in a state that they can be maintained by those with less expertise after the original authors have moved on). Tarl.Neustaedter (talk) 06:15, 9 December 2014 (UTC)
I would be strongly against that. A reader interested by the formula necessarily has a scientific background, and will be able to figure out the "translation" needed between the formulaes in the paper and those of the wikipedia article. And if such an argument rises about "wrong variables", it can only be raised by contributors that lack any scientific background, which disqualifies them to discuss the point in the first place. For a non-scientist to pretend maintaining such a section would be pure folly - like trying to edit Seifert fiber space without any proper mathematical background. Biem (talk) 15:29, 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)

I think the section is just about fine now with that introduction. Biem (talk) 15:29, 9 December 2014 (UTC)
I disagree that the section is just fine. And I disagree with the thrust of Skyway's comment that a good source should match our equations. To the contrary, this article should match the sources we have. If we aren't summarizing the sources we are using, we're trying to be a primary source instead of a tertiary source. Again, this isn't the place for us to demonstrate our acumen and come up with new equations. It's a place for us to summarize what's published elsewhere. Tarl.Neustaedter (talk) 19:10, 9 December 2014 (UTC)

its posible to atach it directly to a moon instead of a counterweight?[edit]

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)

No. Tarl.Neustaedter (talk) 16:23, 17 February 2015 (UTC)
Off the top of my head, I expect the tether would need to be able to extend when the moon is farther away from the planet, since orbits tend to be elliptical, rather than circular. Also, the planet or moon would most likely wobble too much for rails to work, even if their equators were in line. There would probably be other problems, as well. —PC-XT+ 21:14, 17 February 2015 (UTC)