Talk:Space elevator/Archive 5

This is an archive of past discussions about Space elevator. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Archive 1

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Archive 3

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lTAPER CALCULATION WRONG

i believe the taper calculation between earth and geo is wrong. it is exp [p/s * (4.8*10^7]] this agrees with the taper calculation on Pearsons paper

Cable base at 40 km altitude / baloon shuttle

The atmosphere is part of the Earth. Earth surface is about 100 to 120 km atop the sea level !!! While living INSIDE the Earth at the interface between the atmosphere and the lithosphere, we very well know how to climb through the atmosphere and reach a fixed point with helicopters and baloons, no need for 100km towers. Gas baloons can easily get up to 40 km in the stratosphere and serve as shuttles for delivery/recovery of payloads to the base of the elevator. 40 km higher base implies very significant reduction in cable masse and width alowing for lower strenghth requierements. sorry for my english and thanks for your time :)

POV, but don't ask me...

I agree that, especially in the political issues section, a lot of time is wasted exposing rather obvious issues like 'we will have to decide who gets to use it and when?' I think everyone knows that already. Furthermore, there is definite leftist POV about togetherness and international cooperation and sustainable technology and other buzz words with far reaching implications. Those implications include the shutting out of the private sector, the use of hard-earned money of citizens who might not want to fund such a venture, the lack of respect for state sovereignty, and the ability of a public venture to needlessly politicize what could potentially be a peaceful, free-market venture. I'mm not saying this debate should take place on this page, perhaps just remove that section or clean it up to make it encyclopedic. Lumano 05:19, 24 October 2005 (UTC)

Hmm... looking over the talk page, I can see this is a somewhat controversial article, so quite frankly, I'd rather not get involved, but an anon just added some content that reads like someone's personal POV essay rather than like encyclopedic information, ie: unqualified statements about government motivations, etc.: http://en.wikipedia.org/w/wiki.phtml?title=Space_elevator&curid=29192&diff=0&oldid=0 func (talk) 21:04, 27 Nov 2004 (UTC)

(Above lgoes to latest edit, but the datestamp and context indicates he is referring to the anon edit of Nov 25: http://en.wikipedia.org/w/index.php?title=Space_elevator&diff=8027958&oldid=7847322 )

I agree with Func that the anon edit of Nov 25 is POV. It is hardly settled what the roles of governmental, inter-governmental, and private organizations should/would/will be. This is perfunctorily acknowledged a few times, yet there is a clear POV here. In some cases this may have been entirely unintended due to basic assumptions made by anon. Examples (admittedly cherry-picked):

made possible because of the savings made by governments in accessing space - many industries and organizations stand to benefit, and only mentioning one implies an special importance. It may well work out that way, but it oughtn't be assumed. Is this even relevant?
At present, only governments are able to spend that sort of money in the space industry - I don't think this can or should be stated as fact. Seems like the Wal-Mart heirs could scrape together US$5B between them, not to mention Gates, Buffett, Allen, M. Dell....I have *zero* interest in resuming the economics debate here, but can we take it as given that all sorts of industries, organizations, and individuals would stand to profit, even indirectly, from low-cost space delivery? This greatly enlarges the pool of potential investors beyond the Forbes list.
from a political standpoint there is a case to be made that the Space Elevator should be an international effort like the International Space Station with the inevitable rules for use and access - Likewise there is a case to be made that long-term international efforts inevitably fail to accomplish anything (ISS indeed!). While my own POV is no more appropriate here than anon's, it is certainly not less so.

From the same edit, the mentions of benefits to health care, education, etc. probably should be de-POV'd and moved to the general overview paragraph, and mentioned again in the Economics section. It is also unclear to a layman what is meant. We know why education might be improved or medicines might be cheaper, but this article isn't just for us.

Other proposed edits to Politics section:

The frequent references to the US military verges on POV, as those statements are really applicable to any space power -- ongoing US space superiority is hardly guaranteed even as things stand today. One might just as well theorize that the US would *back* a space elevator in order to maintain supremacy. I think the military issue should be stated in as general a manner as is possible.
The issue of ownership and political control is not new here. Weapons technology, steam power, nuclear power, etc., it's been dealt with many times before, and history shows that once a new technology becomes viable it will be seized by anyone who is sufficiently determined. That point is even made later in the politics section. I consider this an internal contradiction -- perhaps a result of the reorganization(s)?
There is the notion that opening space to exploration would erode the relevance of national borders anyway. Indeed this is implicit in all of these political issues. Is discussion of a free-market path appropriate here? Or speculation about each space-elevator becoming a wholly separate political entitity? (Remember the Spacing Guild from Dune?) As it stands this is a rather technical article, such speculation may be out of character -- OTOH this *is* the politics section, and such is the nature of the beast. I think the possibilities at least deserve mention.

I have no wish to dominate with my own POV, just seeking balance. I think some of these changes are clearly justifiable, yet with this many I figure I'll bring it up for discussion first.

--EllisWyatt 00:58, 20 Jan 2005 (UTC)

Don't forget that POV is *not* incorrect in Wikipedia (see NPOV). If you have a contrary view and you can back it up with references add your own POV. - Wolfkeeper

On the basis of the above, I've changed the wording from "...and it is becoming ever more obvious that space is a significant military resource" to "...and it is becoming ever more obvious that space is likely to be militarised". I think the use of the phrase "military resource" quietly condones the use of space as a result, wherease the simple statement of likelyhood is more verifiable. Hughcharlesparker 23:19, August 18, 2005 (UTC)

- I have added a couple of novels. Also there was a mistake where it said "to minimize the weight in the middle" that should be "to minimize the maximum stress that experienced at any point per unit area". -Gunjan

To-do

I have restructured the article a bit. I felt it was awkward before, but there are still some problems.
Partially as a result of my structural edit mentioned above, the text needs to be improved (e.g. by adding an overview paragraph at the beginning of each section) so the sections fit together better
In particular, the article seriously needs a good introduction to the design and physics of a space elevator before going into details about the components
The article is too large, so some text should be moved to specialized articles (as was done with the economics section). This might require additional restructuring to the article. Ideas?
External links must be separated from references, and all external links need descriptions
A few diagrams would be nice.

- Fredrik | talk 09:46, 15 Dec 2004 (UTC)

Interesting, by the way: apparently my structural edit got broken into three (check the page history). There must have been some issues with the database, as saving did take a while and I got an error message while previewing. The end result seems correct though. Fredrik | talk 09:50, 15 Dec 2004 (UTC)

I have added one diagram. Did I get the details right? Fredrik | talk 12:31, 15 Dec 2004 (UTC)

Very nice; looks good. I would be tempted to poke around on various NASA sites looking for a view of Earth from the pole to put in, but that's hardly necessary. Is the diagram to scale? Even the longest cable proposals are only about 20 earth radii long; it might be nice to emphasize the size of the project. --Andrew

I tried to find a good shot of the pole, but unsuccessfully. The altitude is not quite to scale (off by a factor of two or so), though I considered the option. I think it would possibly be confusing since the climber and counterweight can't be drawn to scale. Fredrik | talk 15:05, 15 Dec 2004 (UTC)

What about some simple calculations, and best guess numbers, as to journey time, likely weight limits, that sort of thing. The average reader, like me would like to know what this thing would most likely be capable off and what it wouldn't be capable off. Ian —The preceding unsigned comment was added by 162.61.65.5 (talk • contribs) .

But is this Wikipedia:Original research? -- Zondor 12:46, 8 February 2006 (UTC)

Is NIAC corruption relevant?

Wolfkeeper moved some comments about NIAC from the article body into references. While this may be a good decision, I am not fully comfortable with the article's current position towards Bradley. While I intend in no way to question his qualifications, he is currently called "a leading authority on the space elevator concept", which may not be the most accurate statement. Bolonkin gives a detailed description of corruption in NIAC [1] and also strongly criticises the report by Edwards and Cassanova, saying that "The 42-page report [which costed taxpayers almost 1 million dollars], half of which is mere illustrations, represents a mere explanation of the idea of the space elevator intended for elementary school pupils." [2]. I think that this information should be reflected in the article in some form, and our praise for Edwards should be somewhat limited. Paranoid 18:25, 17 Jan 2005 (UTC)

Well, I think he has done more than this:

he suggested that it might be built in the near future, as in 10-15 rather 50 years
he suggested the technique of installing a seed elevator and building it up from the ground
he suggested ribbon construction techniques, again I've seen that nowhere else

Still, the beanstalk idea has been around for quite a while, and has been worked on by plenty of people. If you have any information to *add* to the article, go ahead. But try not to delete anything as that violates wikipedia's [NPOV].

-Wolfkeeper

First, I don't see why deleting something unneeded would violate NPOV policy. Second, I haven't actually deleted anything from the article, I *added* information. Third, I am not saying Edwards is a fraud. For all I know he might be a genuine space elevator specialist and enthusiast, who has to work within the system, even if that means accepting money on questionable terms.

Even *if* the guy awarding the prize is corrupt, there's absolutely no evidence in the article to suggest that Edwards is.

May be it's so. Still, the fact is that the report for which he got a grant from NIAC was criticised for not being very substantial and not worthy of 1 million.

I disagree. A whole bunch of people now actually think that the Space Elevator can be built in the near future, rather than the far future. And he has come up with a plausible technique and design for doing it. Is that worth $1 million? Who's to say it isn't? He has raised interest in carbon nanotubes, he has very probably created work for material scientists across the globe. There are now yearly conferences on Space Elevators, people are doing conceptual work on what they would look like etc. etc. It seems to me he has created something of value, something worth more than $1 million to all the research scientists.

It was also asserted that this grant proposal was not approved by a real review panel.

I think that that would be much more appropriate under the NIAC entry. Why don't you create the NIAC entry and include it?

It may very well be possible that Edwards is just an opportunist.

My take on it is that NIAC is intended to pay people with interesting ideas money so that they can push the boundary and see where it leads. It's clear that the ideas will mostly *not* pan out. I've worked on R&D. It's a very difficult thing to work on- the difference between an idea that cannot pan out, and can pan out with some careful thinking is very unpredictable. That's partly why the NIAC award process is 2 part.

I also think that of the two stages, Edwards first stage was worth more than he was paid, the second stage he'd run out of ideas. Overall, over the two stages, I don't see that he didn't deserve the money, on the contrary, I think he did.

The NPOV policy suggests that we include Bolonkin's view. I am just trying to determine what would be the best way to do this. Perhaps I didn't state t hat clearly as a question in my previous comment, so I am doing it now. How we should include this information (or why we shouldn't)? Paranoid 09:07, 18 Jan 2005 (UTC)

IMO Criticisms of NIAC should go on the NIAC page. Criticisms of whether Edwards deserved to get that much money or not; it's probably best to only mention in Space Elevator; this piece is about Space Elevators, not Brad Edwards. I do think though that R&D funding is the kind of thing that is extremely easy to criticise and very, very difficult to do well. Personally, I think that the Space Elevator concept *should* have won the awards.

Incidentally, I think that the Space Elevator page could do with much more history, particularly including Konstantin Tsiolkovsky, Clark etc. etc.

I agree that the report would be worth the $1mln even if it turned out both Edwards and Cassanova were frauds and the report was plagiarised from a geocities webpage. The publicity for the space elevator idea is worth the money NIAC paid for it. However, the fact that Edwards was paid 600 thousand for the report doesn't necessarily mean he is a good specialist in this area (especially if the money is awarded in a very questionable way). So why do we call him the "leading authority"? The "most financed scientist"? Sure. But to be a leading authority he needs something more (again, I have nothing against the guy and he may end up being the LA). In the very least it is not justified to call him that. Paranoid 18:42, 18 Jan 2005 (UTC)

some additional ideas

The center of mass of the space elevator must be higher than the geosynchronous orbit, to exploit Earth's angular momentum when the climber goes up. If its center of mass is exactly at the geosynchronous orbit, it becomes unstable as soon as the climber goes up because of Coriolis force.

_{In addition, it is possible to build a space elevator away from the equator, even near the north or south pole. It is good because we can build it in politically and economically better places such as in the U.S. and we can avoid satellites on the equatorial plane. The weather will be worse than that on the equator, though.}

The space elevator involves something that ideally orbits over the same point on the ground. This implies no elevator over the poles. Unless the orbit matches the earth's rotation, the tether will swish over the whole planet.----

  ___|___
 /   |   \
/    |    \______
|    |    |      \---------------O counterweight
|    |    |
|    |    |
\    |    /
 \___|___/
     |
    axis

(Sorry for the poor figure.) The space elevator is stable if it circulates Earth geosynchronously at an orbit where the three forces of centrifugal force, the cable tension, and Earth's gravity cancel. The latter two forces don't have to be perpendicular to the axis, as far as their combined force is perpendicular. This orbit is away from the equatorial plane. - TAKASUGI Shinji 06:56, 9 Mar 2005 (UTC)

Is the "center of mass" really the critical feature? I agree in that it must lie "higher" than geosynchronical orbit, but this results automatically since the crucial concept seems to be the fact that the *sum* of centrifugal force and earth's gravity is zero in any point of the cable. Or am I wrong with this notion? Hochnebel 14:08, 11 Mar 2005 (UTC+1)

if I've understood you correctly... the whole cable is *necessarily* under slightly more tension than the theoretical minimum necessary, so the sums don't quite cancel. And that's because the center of mass is above geo. And if it wasn't, then elevator would lean slightly, pushing the CofM below GEO and then it would actually fall right down to the ground.

-WolfKeeper

Well, center of gravity, technically. And the altitude of geostationary orbit is the only point along the cable where (F_c + F_g) = 0. Otherwise, you wouldn't need the incredibly strong cable to keep things from falling or flying away. The CG of the cable has to be higher than GEO or you've got no payload capacity; the system needs enough buoyancy to support its maximum load, plus a safety factor.

—wwoods 16:59, 11 Mar 2005 (UTC)

No. The center of mass has to be above GEO for the elevator to be stable. Atleast, I'm fairly sure, and see Bertrand Gassende's page at http://www.mit.edu/people/gassend/spaceelevator/center-of-mass/ says the same. The center of gravity can actually be below GEO due to the non linear gravity that the earth and the rotational non-inertial frame of the Earth. WolfKeeper

I wanted to say the center of (gravity + centrifugal force).

The figure below shows a space elevator on the equator seen from the north. Earth's surface is moving eastward.

         O counterweight
         |
         |
         |
         |
 Climber O→ Coriolis force
(goes up)|
         |      
---------+-----------
East     ←     West
       Earth

When the climber goes upward, the westward Coriolis force is produced, which is the same as the force necessary to accelerate the climber's speed eastward to keep the same angular speed. Remember each point of the space elevator has different speed, though they have the same angular speed.

Now, because of the Coriolis force, the whole elevator above the climber is dragged down because of the cable tension.

           O counterweight
           |↓(dragged down by tension)
           |
           |
           |
   Climber O→ Coriolis force
(goes up) /
         /      
---------+-----------
East     ←     West
       Earth

Because of this, the center of (gravity + centrifugal force) must be higher than the geosynchronous orbit even when the heaviest load is on the climber.

The westward shift of the space elevator is automatically recovered because the centrifugal force is stronger than the gravity. See the figure above upside down and treat the elevator like a pendulum. Thus we don't have to accelerate the climber eastward. - TAKASUGI Shinji 03:20, 13 Mar 2005 (UTC)

Conservation of momentum. Initially the elevator has no load and is assumed to be vertical, but a low-momentum load is being raised. The total momentum will be reduced at the end of the process and the elevator will not return to vertical.

Sorry that's not correct. The momentum of the Earth-tether-payload system is conserved. Because the payload has increased in speed, the Earth-tether must have slowed. Since the tether is attached to the ground, the Earth has slowed (minisculely), and because the tether is attached to the ground, it too has slowed).WolfKeeper 20:11, 16 February 2006 (UTC)

If the line is always taut, which is not advisable since this implies the earth is pulling the whole contraption around and around, and if the line breaks the whole thing will just fly off.

The idea is that the tether is always taut. Yes, something like that does happen if the line breaks.WolfKeeper 20:11, 16 February 2006 (UTC)

But there is no pendulum because everything is falling.

No, there is a pendulum because the centrifugal force acts directly away from the center of the Earth, whereas the tension acts away from the attachment point on the Earth. This means that when the cable is tilted, the centrifugal force is no longer inline with the cable, and in fact pushes it back towards the vertical.WolfKeeper 20:11, 16 February 2006 (UTC)

A load plucks the line and causes a wave, but when everything settles down due to heat loss, everything will have sagged. Conservation of energy, i.e., no free lunch, means something needs to be done regularly to lift the whole system back to its original place. ----

No, the energetically most stable position for the cable is vertical, since in that situation the center of mass of the cable is furthest away from the Earth (There's a potential energy field set up by the rotation that opposes the gravity- it goes as r²). It requires *extra* energy to move it away from that position; as that energy is dissipated in various ways the cable returns to the vertical.WolfKeeper 20:11, 16 February 2006 (UTC)

One possible design I thought when I read the article was to use The Quantum theory on how to move the elevator. If you could separate the Elevator's quantas, as quantas come as pairs, to leave one of the two quantas in the elevator, and the other one in the destination; then, by attaching the destination's quantas and making them to not move, you then would make those quantas to "move up" or to move them in the opposit direction than the elevator, so then the elevaotr's quantas will move, making the elvator travel. It's just a thought maybe you could check it.201.155.99.44 04:32, 22 April 2006 (UTC)ANDRES VALENCIA, MEXICO CITY, 2006201.155.99.44 04:32, 22 April 2006 (UTC

space elevator humor

Should we have a "space elevator humor" section in the article ?

- I wouldn't have thought so, it doesn't seem very encyclopedia-like Wolfkeeper 00:35, 6 Apr 2005 (UTC)

Well, that's what talk pages are for! Eh? Right. So, anyway, a rabbi walks into a space elevator with a poodle under one arm and a big feather in his other hand... Beanluc 00:28, 26 October 2005 (UTC)

impact of falling cable?

Section 3.5 reads "the devastation created by thousands of tons of cable striking across hundreds of miles at terminal velocity could have unimaginable effects". Posts on slashdot.org, however, suggest that there might be very little devastation. To quote from this post:

The surviving fragments of an orbital tether would not have the requisite mass to produce the sort of wave disturbances you postulate. Actually, from most accounts, the worst health hazard resulting from a broken orbital tether would be small fragments of nanotube floating about in the atmosphere, eventually drifting to ground level and getting lodged in the lungs (as it turns out, carbon nanotubes are about the same size as asbestos fibers...perfect for getting lodged in the lungs).

Also, to quote from this post:

That's why you don't build it as a cable. You build it as a ribbon, with lots of surface area. If the ribbon snaps, portions high up in the atmosphere will burn up upon reentry. The portions of the cable that don't burn will flutter to the ground - think tickertape parades.

I don't know enough about the issue to make any comments, myself, but the above seems to suggest that a bit more justificiation as to why (or why not) a falling cable would have a devastating impact. TerraFrost 19:59, 13 Apr 2005 (UTC)

You're right, that section greatly overstates the effects (as well as using dubiously scary statements to suggest the effects can't even be predicted). Space elevator#In the event of failure already discusses what sort of impact a break in the elevator would have, so I'm going to trim those bits out of the sabotage section. If someone wishes to dispute it then that's where the text should be disputed. Bryan 01:00, 14 Apr 2005 (UTC)

The falling cable would have a limited (even if high) speed at falling, so there would be time for early warning of affected areas.--Deelkar (talk) 19:35, 30 Apr 2005 (UTC)

Are there any proposed solutions to the failure cascade problem?

The "Meteoroids and micrometeorites" section of the article describes how minor damage would be expected to cause cascading fiber breakage and destruction of the cable. Has this been addressed in the literature, and is there a proposed solution to the problem?

Well, Freeman Dyson's view on the problem is that space elevators will not work because of this problem: "but I am willing to be persuaded wrong". If a man who showed mathematically that it might be possible to use nuclear bombs as a propulsion device to launch from the surface of the Earth thinks it looks tough, IMO it may be a difficult problem to solve. WolfKeeper 00:47, 2005 May 3 (UTC)

Interesting. Can you supply a citation for this?

http://news.com.com/Lets+colonize+space+for+fun,+noted+physicist+says/2100-7337_3-5632246.html

"I am on record in saying that it won't work, but I love to be proven wrong," Dyson said, noting that the elastic energy would have to be equal to the chemical energy required to send a rocket to space. "If it tears in one place, it is likely to be a disaster."

WolfKeeper

An edit and its motivation: In the summary, the sentence

A considerable number of other novel engineering problems would also have to be solved to make a space elevator practical.

has been changed and expanded to:

A range of other novel engineering problems must also be solved to make a space elevator practical, but most have proposed solutions. However, one critical problem, cascading fiber breakage, apparently has no proposed solution (see below, "Meteoroids and micrometeorites").

The change to the first sentence tightens it up and then notes the existence of potential solutions to a wide range of problems. The added sentence notes what is, to the best of my knowledge, a unique issue in that it is potentially fatal and as yet unaddressed, with no proposed solution. I believe that this issue is important to evaluating the space elevator proposal, and should be highlighted in part to stimulate efforts to address it. Note that Wolfkeeper (above) found that Freeman Dyson sees this as a critical issue.

I am sure that this change will be unpopular because it highlights a serious problem in a popular idea. Potential criticisms might be:

1) That the problem does not exist (but it is easy to see that it is real).

You don't know that. It critically depends on the failure modes of a material that doesn't even exist yet. The spring energy in the cable is similar to the energy in an explosive. As the cable contracts it may very well vaporise. It is very unclear whether vapour would damage the cable; and anyway it may well be possible to introduce 'fire breaks' at multikilometer distances or something to stop the problem propogating. Don't forget that the cable can be shaped like a hoytether, the entire cable needn't fail due to one impact.WolfKeeper

The speed of motion of a broken fiber end -- very roughly 1,000 m/s -- isn't a matter of speculation, but of simple physics (conservation of energy and momentum). Unlike the situation in an explosive, the energy can't appear as heat without a further step (stopping the motion of the fiber). If the fiber were somehow braked to a stop, the resulting thermal energy would be enough to raise its temperature by (very roughly) 1,000 deg C. (This is a consequence of conservation of energy and of the heat capacity of graphitic carbon.) This is a nasty temperature, but far short of what is required to vaporize carbon.

It doesn't even have to stop to get hot. Merely contracting the cable makes it hot. WolfKeeper

There is a weak effect of this sort, but the increase in temperature is about the same as the decrease caused by stretching, which is very small (it depends on the anharmonicity of the interatomic potentials, which is small in the working-stress range. By the way, a rubber band actually cools when it contracts, because its elasticity comes primarily from changes in the entropy of the polymer chains. It's fun to try it: take a rubber band, stretch it hard, and touch it to your lip. Detension it, touch again. Repeat a few times. You should notice a substantial temperature swing. (By the way, I do know what I'm talking about on this stuff, which may have to do with a graduate degree in aerospace and considerable background in physics.)

By saying that the problem exists, I mean that (unlike, say, the idea that alien brainwaves will break the cable) this is a problem requiring explicit consideration. This means applying basic physics to proposed designs to get some idea of what happens. Until this is done and a plausible case is made that 1,000 m/s debris can be dealt with, the problem remains. I am shocked that I can find no discussion of this issue. The absence of discussion was noted in the entry last January, and no one has reported finding a discussion since.

Maybe a hoytether structure with 'fire breaks' can do the job. I wouldn't be greatly surprised either way. But until someone looks at this very basic question, it's hard to take space elevator designs seriously.

Is there any other basic, potentialy fatal problem that is known, yet hasn't had any visible analysis at all? If so, I'd prefer that it, too, be separated out from the problems that already seem to have good answers. Open questions need to be highlighted, not hidden.

2) That the problem has a known, in-principle solution (which it may, at some point).

3) That the problem -- which questions the proposal as a whole -- should be buried with others that do not.

Protection from meteoric debris

Perhaps a shield of some sort could be constructed after the space elevator becomes load bearing for cargo. Something shaped like an open, windblown umbrella, with the handle being a small diameter shield around the cable ?? meters, and the larger lower section designed to deflect debris coming in from a higher orbit at an angle. These shields would probably have to have manuevering systems built in to move with the tether, which would add a refueling cost to the tether, plus increased maintenance to ensure the tether shield would be reliable. We could use the multilayer shielding ideas that have been used for the space station, with improvements of course. Just a thought...

The Stub Maker - Zotel

The Van Allen Belt's Impact on the space elevator

I moved this material back from Van Allen Radiation Belt (it was moved from here to there, but really is too spcific for that article). However, there is already a section on radiation hazards in the article. So I'm leaving this here.RJFJR 02:45, May 11, 2005 (UTC)

When the Apollo astronauts travelled to the moon the astronauts received about 1% of a lethal dose in the few hours they were crossing these regions of space. By way of contrast a space elevator will spend anywhere from hours to weeks in these regions, and if the final destination is geosynchronous orbit, the length of stay could be indefinite. Without shielding, this could pose a serious risk to passengers.

As with nuclear power, the problem is that the necessary radiation shielding is very heavy - much heavier than the people it protects; having to lift the passengers as well as the shielding may increase the ticket price many times over the equivalent quantity of freight (since most freight wouldn't be affected by radiation issues and doesn't require shielding).

The radiation belts are based on Earth's magnetic field, which is tilted at about 11 degrees from its rotational axis. They are further distorted by the solar wind, giving them a teardrop shape. Due to this, the elevator will encounter varying intensities of radiation; especially concerning is the inner belt.

One proposal for two way elevator systems to deal with the outer belt is to have extra shielding "in-place" along the cable that is carried up by a climbing elevator, and carried back down by a descending elevator to meet the next elevator carrying passengers up. While this adds constant weight to the elevator (as if a "permanent payload"), it adds the weight to the elevator where the cable is thickest and most able to tolerate extra payload. The "weak point" of the elevator is where it meets the Earth, and shielding is not needed there.

Another type of shielding is so-called "active" shielding. One such type involves electromagnetic fields to deflect low-energy radiation. Another type of active shielding is the Multilayer High Temperature Superconductor Protection System, which involves using high-temperature superconducting materials to produce strong magnetic fields for deflection. [3]. In theory, anything that produces a strong magnetic field could be used to deflect the radiation, but the strength of the magnetic field produced given the weight of the materials required can be a limiting factor. Active shielding, in its current designs, is very effective at shielding from protons of energies up to 200MeV, but is largely ineffective against galactic cosmic radiation (GCR) [4]. As the dangerous inner Van Allen belt consists mostly of protons from energies between 10 and 100 MeV, and particles in the outer van allen belts are lower energy (around 1 MeV) [[5]], active shielding is a realistic option for the transit up to GEO. However, since it is ineffective against GCR, long-term human stays at GEO would require physical shielding in the structure they are to stay at.

There is also a proposal by the late Bob Forward called HiVolt which may be a way to drain at least parts of the Van Allen belts to 1% of their natural level within a year.

Mechanical climbers on the space elevator could draw energy from the belts as they travel through it. This would provide some power to the climber, and, after several thousand climbs, the belts would be reduced to a tiny fraction of their original intensity.

Where did you get this bit from? It sounds prima facie implausible, and even if it worked (I doubt it), where does that get you if the power is gone after a few thousand climbs?

So what gives? WolfKeeper

I got this from the article on the van Allen Radiation belt. I just moved the section here. (I suppose we could go through that article's edit history and look for who added this material). I beleive this material was originally here in some form (it was probably edited while it was at that article). Myself, I'm kind of suspicious of the HiVOLT idea, but I'm not quite qualified to say it wouldn't work.RJFJR 01:24, May 12, 2005 (UTC)

Cable Taper Calculations, necessary?

This article is causing a length warning. Looking through it the Cable Taper section looks expendable. I considered moving it to its own page, but I didn't think it would have enough context to make sense. Or we could just delete the whole thing, but I like the 4 points at the end. Anyone have a good idea about this section? RJFJR 02:45, May 11, 2005 (UTC)

We could move it to a new article called "Space Elevator Physics" -- Klafubra 13:09, 17 May 2005 (UTC)

Space elevators as an energy source?

Could a space elevator be an energy source by using the thermal/electrical differential between Earth's surface and cold space/the ionosphere? Ultramarine 19:54, 12 May 2005 (UTC)

I had a similar thought - it also occured to me that an electrical current might be induced from the Earth's magnetic field (or would it's non-motion relative to the earth prevent this?). I suppose in both cases the answer might depend upon the materials used in the construction of the cable.

In any case, a good deal of energy can probably be generated by conventional means on the downward leg - perhaps enough to greatly subsidise the upward trips?

I haven't read anything about thermal. The closest analog I can think of is ocean thermal, but with hot and cold air. You can't use motion through the Earth's magnetic field, because the tether is in geostationary orbit. However, I don't know whether simply connecting the ionosphere to ground gets you current (anybody?). I do know that carbon nanotubes conduct electricity well and that lightning strikes are a concern.

I have read that the space elevator will pay for itself quickly because it makes solar power satellites profitable. So perhaps more as an enabler, rather than a source itself. --noösfractal 06:42, 27 September 2005 (UTC)

Space elevator or Beanstalk

user:Wolfkeeper moved most of the article to Beanstalk, which was previously a redirect here. I changed both back. I didn't care if he moved all the article there, I objected to moving part of the article.

I am of the opinion we should pick one name and have the other redirect to it. I don't care which is which I just don't want part of the text at one and part at the other. They look like synonyms to me so have one article.

They aren't. That's the whole point.

A beanstalk is a cable from geo, whereas a space elevator is anything that is connected to a planetary body that reaches space. That's *not* the same thing. Designs exist for very tall, spindly towers that reach 100km for example, that's space. Or there's a design for a rotating orbital ring that has spokes hanging down off bearings. Or the space fountain idea. The point is that they are *not* the same.

Just like a lion is a cat, but a cat is not a lion, a beanstalk is a space elevator, but a space elevator is not a beanstalk. WolfKeeper

(That is different than the proposal to have a seperate article on the physics of the space elevator, which would result in a more focused article and one that meets the length recommendation. I like that idea.) RJFJR 15:56, May 20, 2005 (UTC)

(If it gets moved then the talk page should go with it. RJFJR 16:02, May 20, 2005 (UTC))

I disagree with moving the article. Your point seems to be that a space elevator is 'any method of lifting cargo into orbit', which is rediculous.

Yes, that would be. Which is why it wasn't my point. My point is that *a* correct name for a geosynchronous orbital tether is 'space elevator', and then listed a number of other concepts that are also space elevators.

The space elevator concept refers specifically to an elevator, with the cable, and the elevator-cabin, and the moving up and down.

But all the tall structures have that. Isn't that the whole point, that there is an elevator, a cable, a car, and it goes to space? The geosynchronous orbital tether is just one example.

A beanstalk, to me, is what you get when you plant beans. -- Ec5618 17:05, May 20, 2005 (UTC)

Yessss. What a shame that the english language doesn't permit more than one definition of a word. Oh! Wait! WolfKeeper

I think Wikipedia must be descriptive of terminology use, not prescriptive. I haven't done a rigorous survey, but it seems to me that when most people these days talk about beanstalks, they use the term "space elevator" to describe it - all ten of the top Google results for "space elevator" are focused on the cable kind (though one's Wikipedia itself so that doesn't really count :). Furthermore, "space elevator" gets 2.3 million hits on Google compared to only half a million for "beanstalk", so I think we should probably go with that. Bryan 23:36, 20 May 2005 (UTC)

Heh heh. I already did much the same thing; I wasn't exactly planning on going through the wikipedia removing 'Space Elevator' and putting 'beanstalk' though. WolfKeeper

Actually, I was only arguing about where to put it in the wikipedia, not trying to redefine anything, I certainly agree that most people do use 'Space Elevator' for geosynchronous orbital tethers and I agree that they are Space Elevators. But there is a structural problem here because the article reads like a Space Elevator is only that; and it looks like half the contributors think that too. Heck, maybe it is, there's nothing that says that a Space Elevator is an elevator that goes to space, if every word or phrase meant exactly what it sounded like we wouldn't need dictionaries, but I'm not aware of any firm definition of it anywhere. WolfKeeper

OTOH, a beanstalk is unequivocally a synchronous orbital tether, so putting it there is correct, but some people evidently absolutely loathe the term. Space Elevator has less precise connotations, but is somewhat more generic and popular. WolfKeeper

We could consider moving the bulk of the article to 'Synchronous Orbital Tethers' but perhaps some people would hate that more than sticking it under beanstalk. WolfKeeper

How about we leave it here, redirect everything to here and add a section to the intro about what redirects in and the subtle (or not so subtle) distinctions? (I did a google on "space elevator" beanstalk' figuring the pages would either tell me they were the same or different...it didn't work.

I still claim that they aren't necessarily the same thing. Unless you believe that a space fountain isn't a space elevator. I considered that, but I decided that it was.

But I did see one claim that trying to build a structure to orbit was impractical and hence the cable down from the top idea.) RJFJR 18:30, May 21, 2005 (UTC)

What? This link you mean: http://umich-web0.everything2.com/index.pl?node_id=1334678 ? If so, yeah, I wrote that :-) Note that there's a distinction between *orbit* and *space*. They are NOT the same thing. Also note that everything2 isn't really an encyclopedia, it lacks precision, and you end up tailoring your articles to what would fly there.WolfKeeper

The intro already has mention of both space fountains and tall compressive structures, with a link to the space fountain article. Are you thinking of making it more like a disambiguation section at the very top of the article instead? Bryan 18:45, 21 May 2005 (UTC)

External links and footnotes

To keep it up to FA level, please remove external links from text, move to references and link back to relevant sections with Wikipedia:Footnotes. --Piotr Konieczny aka Prokonsul Piotrus ^Talk 9 July 2005 18:10 (UTC)

Organizations

I wish to start the practice of showing when the External link was last updated and by whom. On fast changing technology it is a pain to re-visit a web site that has not changed since visited last. If we can keep update dates noted in this section then it may encourage the External site to stay current and updated. I have taken the liberty to do this to an Organization link here. What do others think? (and to note if the link to the site is broken)

Space elevator, Institute for Scientific Research - added -> "Last news item dated July of 2004." --Bobwinmill 16:06, 13 September 2005 (UTC)

Spoken Article

I would personally love to read this and make it into a spoken article, but I'm completely unfamiliar with the process and would require some guidance from a more experienced wikipedian...(although I've been told I have a good voice and would love to use it for the betterment of mankind)...if anyone is interested in assisting me in this endeavor, please contact me...my aim sn is liberty484 and my email is antiantitrust at mail.com. Paul 05:21, 27 July 2005 (UTC)

Economics of Space Elevator

A recent IEEE Spectrum Article had a good article on space elevators.

The main advantage of space elevators would be a large drop in the cost of sending a payloads into orbit. Currently it costs $20,000 (USD) to send a single kilogram into orbit. According to the article, after the first space is elevator is built the cost would drop to only $200 per kilogram. After multiple space elevators are constructed the article predicted the cost could drop as low as $10 per kilogram. In other words a successful space elevator would greatly reduce the cost of getting objects into orbit.

Here's the link for people who want to add to the wikipedia article: http://www.spectrum.ieee.org/WEBONLY/publicfeature/aug05/0805spac.html

That might be better placed over at Space elevator economics. siafu 02:27, 17 August 2005 (UTC)

Obsession with the US Military?

Though this could be true:

"The U.S. military may covertly oppose a space elevator. By granting inexpensive access to space, a space elevator permits less-wealthy opponents of the U.S. to gain military access to space—or to challenge U.S. control of space. An important U.S. military doctrine is to maintain space and air superiority during a conflict. In the current political climate, concerns over terrorism and homeland security could be possible grounds for more overt opposition to such a project by the U.S. government."

Its clearly speculation, and every military in the world have reasons to covertly oppose a space elevator. We could re-write this paragraph to cover the Chinese, Russian, and Indian Militaries, and the Israeli military might very well go bonkers at the thought of their enemies gaining the ability to bombard them from space with material brought up with inexpensive lift capability. In fact a space elevator complicates national defense for everyone, but so does the internet, international trade, and the widespread availability of common household cleansers and cell phones which are now used to make bombs and detonators.

I hesitate to dive in and delete some one else’s work, but it seems to me that there should either be a section speculating about who might oppose the project. This could include just about everyone on earth because who knows what anyone –may- do? Or this one paragraph should be dropped.

This is speculation and original research. Definitely needs to be cut. siafu 17:12, 13 September 2005 (UTC)

Geosynchronous orbit

As mentioned before (but for other reasons) the centre-of-mass of tether isn't at geosynchronous orbit. This is because kepler's laws apply for point masses. Treating extended objects as point masses is only realistic when the gravitational field is uniform.

Also, the tether doesn't really need a counterweight as depicted in the graphic. The tether IS the counterweight.

This pointed out further up on this page. Its easy to show that this must be the case. Infact the CG needs to be quite a long way from Geo. In the case of using a tether as the counterweight, much of the cable would be way past the geo and the dynamics arn't as good. So for the most part there will always be a counterweight. Probably a space station of some sort.

I am going to edit this page to fix the CG issue and replace the graphic. But it won't be untill the weekend.--Delt0r 07:52, 18 October 2005 (UTC)

"Center of mass" and "center of gravity" (CG) mean very different things in this case, be cautious. The center of gravity only needs to be a little way out beyond geosynchronous, and in fact could theoretically be right at geosynchronous if it weren't for the need to lift payloads and provide safety margins. Bryan 08:05, 18 October 2005 (UTC)

Ah, I see the problem now - the diagram uses "center of mass" when it should be using "center of gravity". Changing just that word should fix it. Bryan 08:07, 18 October 2005 (UTC)

Good point. I missed the mixing up of these terms. I think making a clear distinction between these terms may be needed. Most engineers use both terms as equivalent.--Delt0r 08:47, 18 October 2005 (UTC)

Yeah, I've noticed that the center of mass article makes that mistake quite a bit itself. Hopefully to be fixed within the next few days. :) Bryan 00:00, 19 October 2005 (UTC)

Arthur C. Clarke mentions a new material

Hi. Arthur C. Clarke has mentioned the discovery of a new material in a [at Times Online]. Someone with a good background in the subject could consider updating it with this inforation. The text goes as "This situation has now changed, with the discovery of the third form of carbon, C60, and its relatives, the Buckminsterfullerenes. If these can be mass-produced, building a space elevator would be a completely viable engineering proposition." - Yves Junqueira, 2/oct/2005.

Yes, the Buckminsterfullerenes that are potentially useful for SEs are also known as carbon nanotubes. The article already discusses these.WolfKeeper

Don't we have carbon nanotubes?

Recently we have gained the ability to industrialy mass-produce carbon nanotubes. I have read that the cost of construction would be around $10.000.000.000. Why hasn't this new information been included in this page?

Um, because it's unsubstantiated hearsay?

In all seriousness, carbon nanotubes are not mass-produced yet. They are being made in small but increasing quantities, and production process improvements continue to be made. But the ability to produce 1000s of kilometers of 100+ GPa material is not coming along a predictable timeline.

Because the manufacturing process is unknown, these specific cost numbers, be they $10B or the $5B I've read elsewhere, are all nonfactual and should be deleted. At best, we can say that Brad Edwards has speculated that xxx might cost yyy. Iain McClatchie 23:09, 21 October 2005 (UTC)

If I can add a bit to the figure cited? Dr. Edwards has reported (in the NIAC study) a figure of between 4 - 6 billion. No one has worked up a more accurat budget study - possibly because it's hard to assign cost centers to a project we're not sure we can build - Liftport has looked at the budget figures in-house and while we agree it _should_ cost more than 4-6 billion - it's hard to see where the extra money would be spent, or on what.

The 10 trillion figure cited might come from reading earlier estimates from NASA based on asteroid capture and several thousand Shuttle flights. None of which, we think, are required. Brian Dunbar

Tensile Strength

Hi. I noticed that the Space elevator article describes "tensile strength" as being "the limit to which a material can be stretched without irreversibly deforming" but the Tensile strength article states that:

"The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before it breaks."

Upon further reading of the tensile strength article, it looks like tensile strength is divided into "yield" and "ultimate" (the former being the limit of tensile stress which material can endure and retain its elasticity, and the latter being the limit of tensile stress before the material breaks).

Does anybody think that the elevator article should be updated to clarify this issue, and what is the best way to do so? Cheers TigerShark 10:25, 12 November 2005 (UTC)

"the limit to which a material can be stretched without irreversibly deforming" is a poor definition of tensile strength. First of all, "stretch" is a reference to strain, not stress which is the common unit of strength. Secondly, that's a definition of the elastic limit, which is a different concept from yield or ultimate strength. Carbon nanotubes are nearly linear-elastic to failure, which means that the elastic limit and the ultimate strength are quite close, and the concept of yield is not really applicable. Typically for non-ductile materials the ultimate strength is considered to be the limit state, so the usefull definition of tensile strength in this article is the stress (load per unit area) a material can be subjected to without breaking. Toiyabe 23:46, 15 February 2006 (UTC)

Gripes with this article.

The opening section of the article should just focus on what space elevator does, how it works, and stick with the most plausible structure, the tether lowered from orbit held up by centrifugal force. I'd like to rewrite the first couple of paragraphs and move the discussion of space fountains to a later section, or someone else can, here is my list of gripes

The article doesn't open with a clear opening explanation of what a space elevator is... the concept, in plain English
Space fountains aren't that plausible.
Compressive structures aren't defined or linked.

Plowboylifestyle 06:15, 22 November 2005 (UTC)

Beanstalk has to go

I know this has been discussed at length. But face it, the space elevator concept is the geosynchronous orbital tether.Plowboylifestyle 20:16, 26 November 2005 (UTC)

No. Formally a space elevator is a structure that reaches space. space fountains, ultratall buildings etc. etc. WolfKeeper

Incidentally geosynchronous orbital tether is underconstrained- you can have geosynchronous orbital tethers that don't reach the ground. In this context, you can't have a beanstalk that doesn't go through GEO.WolfKeeper

The word beanstalk is nice, it should be mentioned, but it should be replaced by the word tether. Otherwise please proove that beanstalk is in common use. Other names and elevator concepts should be mentioned but not prominent. Plowboylifestyle 20:16, 26 November 2005 (UTC)

Googling beanstalk "space elevator" gives Wikipedia as the first hit, but after that there are numerous other sources that use the two terms together. Removing the term from this article would be inappropriate, and "common use" isn't needed to be listed as a synonym. It's not like the article is at beanstalk, that just redirects. Bryan 20:51, 26 November 2005 (UTC)

You can still have beanstalk in the article. Just don't use it as the main term for a geosynchronous orbital tether. Its not the main term in use. Plowboylifestyle 23:01, 26 November 2005 (UTC)

To put this in perspective, the current first sentence reads: A space elevator, also known as a space bridge or star ladder, is a hypothetical fixed structure from the Earth's surface into space for carrying payloads.WolfKeeper

I did a web search on the term 'space bridge' and I got 50,000 hits. I get 350,000 hits on 'beanstalk space elevator'. As to 'star bridge' I tried a few search terms and got hardly any relevant hits- about 1000. So on that basis we should lose 'star bridge' and replace it with beanstalk.WolfKeeper

In fact it seems to me that there's a strong case for writing A space elevator, also known as a beanstalk or space bridge.WolfKeeper

The point is that beanstalk is actually a correct and reasonably well used term. Many people have an issue with this term for whatever reason, but an encyclopedia has an obligation to reflect the world, not to try to censor it or engage in wishful thinking.WolfKeeper

The most recent revision after my reversion, before the addition of "The term space elevator is usually synonymous with beanstalk" was better than the earlier revision that occurred today; but no amount of colloquial use is ever likely to make "beanstalk" synonymous with "Space elevator" — beanstalk remains primarily a term for a portion of a plant. I actually like the term, but there is too much over-emphasis on it, as if it was already the generally preferred term for the device — which I do not believe to actually be the case. ~ Achilles † 00:28, 27 November 2005 (UTC)

syn·on·y·mous adj.- Having the same or a similar meaning: synonymous words.WolfKeeper

It's not about popularity.WolfKeeper

If I, or a few people I might converse with, were to call a person an idiot, a fool, or use even more generally harsh and insulting terms, or conversely laud someone, sincerely or sarcastically, calling them a "genius", a "hero", or even "the god", then in those contexts I might argue that such a person's name was synonymous to those words for me, or a few others, but that hardly makes any such word or name a synonym in any absolute or general sense.To say something can be synonymous does not carry quite the same connotations as the flat statement that a word is synonymous with another, which implies to many people that the words are primarily synonyms, and not merely incidentally so, in specific contexts, within specific groups.

The statement which was added, and which I objected to, flatly states : "The term 'space elevator' is usually synonymous with beanstalk", and I state flatly that this is usually NOT the case. I have therefore substituted this: "Space elevators have also sometimes been referred to as space bridges, beanstalks or space ladders."

This is closer to the statement previously there: "A space elevator is also referred to as a space bridge or star ladder" but I have dropped the term "star ladder" which I found to have about 800 google hits but primarily in the context of a "ladder towards stardom", or some sort of graphic design; there were only about 119 when "star ladder" & "space elevator" were both included, and even for less ambiguous terms there were only about 155 for a joint search of "space ladder" & "space elevator" and only about 747 for "space bridge" & "space elevator". There were only 635 for a joint search of both "beanstalk" & "space elevator". ~ Achilles † 14:31, 27 November 2005 (UTC)

Achilles † 23:22, 28 November 2005 (UTC) : I am restoring the cohesion of my previous statement by removing four interjections into it which occurred, and placing them below. I believe that it goes against standard Wikipedia etiquette to break up a person's statements in this way, and to someone coming upon the page it could even seem like I had been the rude one, not signing sporadic comments that no longer cohere well. Please stop this practice, as it is extremely annoying. Make your arguments in a coherent way, rather than snipping apart cohesive statements with your sniping.

The interjections that I removed from my statement were as follows — as some ask either rhetorical or sarcastic questions of me I will respond to them, immediately after the question:

1) First, there was a simple comment on the word "beanstalk":

The term is in widespread use though, it's not just a small group, and so I don't feel your argument to be sound here. But that wasn't the point I was making; 'space elevator' is a more general concept. Beanstalk is a precise word for geosynchronous tether to the Earths surface, as is space bridge or star bridge.WolfKeeper

2) The statement which was added, and which I objected to, flatly states : "The term 'space elevator' is usually synonymous with beanstalk", and I state flatly that this is usually NOT the case.

Really? Do you have a reference for that extraordinary claim? WolfKeeper

To this, I must respond that it is hardly an extraordinary claim that most speakers of the english language do not immediately think "space elevator" when you declare the word "beanstalk" ~ Achilles

3) I have therefore substituted this: "Space elevators have also sometimes been referred to as space bridges, beanstalks or space ladders."

That implies that this is incorrect. Do you have a reference for that claim that this usage is unfounded?WolfKeeper

Again: to, flatly state : "The term 'space elevator' is usually synonymous with beanstalk" is blatantly false. It is usually no such thing, for most speakers of the english language. ~ Achilles

4) I have dropped the term "star ladder" which I found to have about 800 google hits but primarily in the context of a "ladder towards stardom", or some sort of graphic design; there were only about 119 when "star ladder" & "space elevator" were both included, and even for less ambiguous terms there were only about 155 for a joint search of "space ladder" & "space elevator" and only about 747 for "space bridge" & "space elevator".

FWIW I only get 622 today. Clearly it will vary, but I have personally never seen a score above beanstalk. Google do experiment, and have been known to return different responses to different parts of the internet for their research purposes.WolfKeeper

To this I can only respond that a few hundred occurrences on the entire Web is hardly an overwhelming endorsement of the widespread or prevalent use of the term. ~ Achilles † 23:22, 28 November 2005 (UTC)

I also wish to make clear that I never argued that beanstalk had to be removed entirely, merely that I agreed with others that it was overused at the point this discussion began. That is no longer the case at this point in time. ~ Achilles † 23:31, 28 November 2005 (UTC)

About this word 'Plausible'

I guess part of the reason I'm down on emphasizing space fountains and compressive structures so early in the article is because they are very much the subjects of fiction, plausable yes, feasable probably not. Where as orbital tethers are the subject of numerous active research projects and one commercial venture, they could very possibly become as real as the space shuttles in our lifetime. I think there needs to be some way of pointing this out early. Plowboylifestyle 21:32, 27 November 2005 (UTC)

On the other hand, "space elevator" is a generic term that can encompass all of those possibilities. Perhaps if there's to be an article specifically about the tether option, this article should be moved to that title (to preserve the article history) and then the first couple of paragraphs cut-and-paste back to space elevator to serve as a general overview and disambiguation page instead. How's that? Bryan 02:10, 28 November 2005 (UTC)

Is there any wikipedia guidelines that describe how to deal with naming conflicts like this. The problem as I see it is that no one has ever really defined the term. So it's whatever someone feels about what is appropriate. I think its fine to refer to a space elevator and mean only an orbital tether. I think most people looking for orbital tethers will look up space elevator. So I think its fine for the space elevator article to be mostly about orbital tethers. Since the other concepts are still mentioned and linked. My issue is with calling them "plausible". I'm not sure that they are. Plowboylifestyle 04:45, 28 November 2005 (UTC)

Google's define function defines 'plausible' as "apparently reasonable and valid, and truthful". I submit plausible in this context means something like "will this work" as opposed to "is this economical to build and operater". I contend that an SE is a plausible system in that it can be shown that nothing about the thing violates known physics, and it will generally do what proponents say it will do.

The open question is; can SE can be built with real-world materials and economics. Jury is still out on that one. 'No' it can't be built today, but 'yes' one can be built given some not unreasonable advances in materials. I'm biased of course, but I think I'm more right than not.brian dunbar 14:17, 28 November 2005 (CDt)

I think the orbital tether is plausible, I think ita going to be built in the next 20 years. I don't think space fountains and compressive structures are in the same category for the simple reason that they are not the subject of actual research. Famous scientists throwing around ideas doesn't count. They are the subject of science fiction. I just think the article should point out this difference. Plowboylifestyle 22:48, 28 November 2005 (UTC)

I think there's still the problem of the two different meanings of "plausible" that Brian mentioned above. You're using plausible to mean "I think the strucutre will be built in the near future", whereas I interpret it to mean "I think the structure could work if humanity actually went ahead and built one." The second meaning is more amenable to objective analysis, one can mathematically model the structure in question and both the assumptions and results are clear. The first one, on the other hand, requires one to make judgements based on economics, politics, social factors, etc. - much harder to make an objective argument about. In both cases a standard NPOV solution to potential dispute would be to state who it is that finds these cases plausible and who it is that finds them implausible, and explain what "plausible" means in each case. Who's analysis do you get that 20 year figure from, for example? If this is too much to put in the intro then the issue of plausibility should be deferred until later in the article where there's space to present all sides. Alternately, we can go ahead with my suggestion to split the article into a generic "space elevator" article covering all of the options and an "orbital tether" article to focus on the beanstalk option. What's now an intro section would become an entire article and it could afford as much space as necessary to compare and contrast things. Bryan 01:00, 29 November 2005 (UTC)

In fact, now that I consider the article a bit more, I'm going to be bold and just go ahead and do that (in a few hours, though, since there's a limit to boldness for something big like this :). The addition of that top-level "orbital tether/beanstalk" header has gone unchallenged for two days now and that's a clear step in this direction already. Any objections? Bryan 01:04, 29 November 2005 (UTC)

Don't do it, you'll just open a whole new can of worms. Space fountain has a great article and a link in the third paragraph of space elevator, the other space elevators would so far be stubs. Try this revision. Plowboylifestyle 02:15, 29 November 2005 (UTC)

I agree here. There is no need or advantage that I can see to such drastic re-working. ~ Achilles † 02:23, 29 November 2005 (UTC)

But the article as it currently stands is already two articles in one thanks to that top-level "orbital tethers" header. The four paragraphs in the intro section talk about all the various types of "really tall structures that go from ground to orbit", and then the remaining 95% of the article is about just one specific type of space elevator. When 95% of the article is about just one sub-portion of the article's topic there's something wrong with the article's structure. As Plowboylifestyle points out, the space fountain material is already off in its own article and I don't think anyone would agree that merging it into here would make sense. Splitting would just do the same thing with the orbital tether stuff that's already done with the space fountain stuff. Bryan 05:34, 29 November 2005 (UTC)

Graphics

Generally speaking I avoid making direct edits to this article, wanting to avoid even the appearance of a conflict of interest. However, some of the graphic images - used with our after-the-fact permission - could stand to be updated. I can do this readily enough by substituting an updated image for ones in place - or would it be better to let a wiki user not affiliated with Liftport do this? See www.liftport.com/gallery for imagery. brian dunbar 14:17, 28 November 2005 (CDT)

Brian, I'm not sure why its a conflict of interest. If one of the other space elevator companies wants to use there images on the page, they are welcome too right? ;) Just remmember NPOV and I think your fine. Plowboylifestyle 21:17, 29 November 2005 (UTC)

Yeah, it would seem kind of odd if there was a problem with people submitting material to Wikipedia that they explicitly have the right to submit, requiring other third parties to step in and submit it instead. If worst comes to worst the old image can be reverted to, just like with old revisions of article text. Out-of-date images might still be useful for illustrating historical concepts. Bryan 06:41, 30 November 2005 (UTC)

Plouwboylifestyle, you asked on my personal page which images from the Liftport gallery were okay to use to update the Space Elevator entry - use any images you want. We're open about re-using those images as long as attribution is made to Liftport Group and they are not re-used for commercial purposes Bdunbar 12:35, 2 January 2006 (UTC)

Base Location

I've just finished reading Clarke's Sunstorm, and in it, as in many of his other books, he mentions the beginnings of a space elevator. However, this one is situated near Perth, and Clarke makes the point of stating that, contrary to earlier beliefs, such an elevator need not be based at the equator. Now in one of his earlier works of fiction, he went so far as to rename and relocate his beloved Sri Lanka onto the equator, so that it could be the base of such a structure.

My question is, how could a space elevator be built other than on the equator? If one was built, say, at Perth, would it pull perpendicular to the tangent of the earth at that point (thus defining a sort of truncated cone), or would it be perpendicular to the earth's axis? I mean, at the equator, these two are one and the same. But how would it be at a higher latitude? And why has thinking changed on this? I scanned the article and seemed to find confirmation that the space elevator does not need to be at the equator, but I still have my questions.

I am, by the way, without any significant scientific education, so feel free to talk down to me. Unschool 00:48, 26 December 2005 (UTC)

Clarke might not have been thinking about weather. I believe the primary reason that Liftport Group wants to put their space elevator off the coast of Peru is because there is a zone around the equator that is between the two main convection cycles of the earth. Very litte clouds there and very little lightning. I think it has less to do with the mechanics of where you place a tether on a rotating sphere. Personally I'd like to see one in Antartica, then you could maybe walk up it. Stairway!!! Plowboylifestyle 05:07, 26 December 2005 (UTC)

I don't know. I remember reading an old article in World Book (this would have been around 1968-70), and it stated that geosyncranous orbit needs to be over the equator--that an attempt to do the same thing elsewhere would result in a figure-8 shaped orbit that would stay roughly on the same side of the planet, but not in one place. The article even had a diagram showing this. Unschool 06:43, 26 December 2005 (UTC)

That too. It's both. Plowboylifestyle 06:50, 26 December 2005 (UTC)

It can be built in locations other than the equator; however you sacrifice lifting capacity and require a stronger cable. In a perfect world you could built on at Antarctica; in the messy real world we think once you move past 15 degrees lattitude it's past the bounds of workable. There was a whitepaper on this very topic at one of the space elevator conferences hosted by ISR - it should be online. brian dunbar

'A satellite orbits an --'

A question regarding language and writing for this intelligent, creative (capable even of creating new physics) responsive forum: What is a generic term for the object a satellite orbits? In other words finish this sentence: A satellite orbits an ----. Do not say heavenly body! Therealhrw 19:30, 28 December 2005 (UTC)

I'm sorry, but I have no idea what you're saying, most of the time. 'This intelligent, creative responsive forum'? What? Who? Where?

In response to your question though, a satellite orbits any object. Two satellites may orbit eachother, and the Earth is just as much a satellite of the Moon as vice versa. -- Ec5618 21:21, 28 December 2005 (UTC)

The wikipedia article on satellites says that when a smaller body orbits a larger body, the smaller is called a satellite and the larger is called the primary. If the tow bodies are of unknown size or near equal sze the two objects are called a binzry system as in binary star system. I am looking for a less confusing word than 'primary' becuse most of my personal axquintainces are super un-educated and are sorely confused if you use a general word like 'primary'. Therealhrw 03:29, 29 December 2005 (UTC)

The satellite article does indeed state that. I don't think there is a less confusing word. If there was, the article would most likely mention it ("which is known as its primary or .."). And I still say that any two objects orbiting eachother could be seen as satellites, so you could just call all objects satellites and distinguish between size in some other way, perhaps by calling the larger object primary satellite, and the smaller object secondary satellite. -- Ec5618 10:45, 29 December 2005 (UTC)

Ec dude's last sentence good answer. Thanks. Ec: Satellite article also says satellite called 'primaey' when center of mass of system is inside said 'primary'. Center of mass of Earth-Moon system is hundreds of miles below Earth's surface. Which is weird, but whatever. Therealhrw 09:30, 30 December 2005 (UTC)