Talk:Space elevator/Archive 6

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Naming Issues

Ok, so I did a whole bunch of googles to find out what terms are most popular:

• Results 1 - 10 of about 1,960,000 for beanstalk [definition]. (0.23 seconds)
• Results 1 - 10 of about 482,000 for "space elevator". (0.26 seconds)
• Results 1 - 10 of about 318,000 for beanstalk space. (0.28 seconds)
• Results 1 - 10 of about 49,900 for beanstalk elevator. (0.21 seconds)
• Results 1 - 10 of about 35,900 for "space bridge". (0.18 seconds)
• Results 1 - 10 of about 27,500 for "space elevator" tether. (0.17 seconds)
• Results 1 - 10 of about 1,210 for "star ladder". (0.07 seconds)
• Results 1 - 10 of about 743 for "geosynchronous orbital tether". (0.40 seconds)
• Results 1 - 10 of about 732 for beanstalk "space elevator". (0.42 seconds)
• Results 1 - 10 of about 594 for "space bridge" "space elevator". (0.39 seconds)
• Results 1 - 10 of about 560 for "orbital tether". (0.48 seconds)
• Results 1 - 10 of about 494 for "star ladder" space. (0.69 seconds)
• Results 1 - 10 of about 370 for "space bridge" beanstalk. (0.28 seconds)
• Results 1 - 10 of about 272 for "space ladders". (0.26 seconds)
• Results 1 - 10 of about 854 for "space lifts". (0.21 seconds)
• Results 1 - 10 of about 151 for "star ladder" elevator. (0.26 seconds)
• Results 1 - 10 of about 134 for "star ladder" space elevator. (0.64 seconds)
• Results 1 - 10 of about 67 for "space lifts" "space elevator". (0.25 seconds)
• Results 1 - 10 of about 49 for "space ladders" "space elevator". (0.36 seconds)
• Results 1 - 10 of about 13 for "star bridge" "space elevator". (0.30 seconds)
• Results 1 - 1 of about 7 for "space lifts" beanstalk. (0.19 seconds)

(Note these will vary over time as pages come and go and as google changes their page rank and so Results 1 - 10 of about 65 for "space ladder" geosynchronous. (0.28 seconds) forth.)

Analysis:

Beanstalk is the most popular, but only because of 'Jack and the Beanstalk'. Clearly 'beanstalk' on its own isn't enough; because beanstalk is ambiguous. If you remove that the correct order seems to me to be: space elevator, beanstalk, space bridge, space lifts, star ladder

WolfKeeper 21:23, 14 January 2006 (UTC)

Ok, so let's append 'geosynchronous' to the different terms to see what we get:

• Results 1 - 10 of about 15,800 for "space elevator" geosynchronous. (0.18 seconds)
• Results 1 - 10 of about 821 for "orbital tether" geosynchronous. (0.52 seconds)
• Results 1 - 10 of about 753 for beanstalk geosynchronous. (0.21 seconds)
• Results 1 - 10 of about 743 for "geosynchronous orbital tether". (0.40 seconds)
• Results 1 - 10 of about 399 for "space bridge" geosynchronous. (0.28 seconds)
• Results 1 - 10 of about 271 for "space lift" geosynchronous. (0.16 seconds)
• Results 1 - 10 of about 65 for "space ladder" geosynchronous. (0.28 seconds)
• Results 1 - 10 of about 62 for "star ladder" geosynchronous. (0.98 seconds)
• Results 1 - 5 of 5 for "star bridge" geosynchronous. (0.22 seconds)

OTOH:

• Results 1 - 10 of about 35,600 for "space elevator" geo. (0.14 seconds)
• Results 1 - 10 of about 18,600 for beanstalk geo. (0.18 seconds)
• Results 1 - 10 of about 255 for "orbital tether" geo. (0.25 seconds)
• Results 1 - 10 of about 250 for "star bridge" geo. (0.33 seconds)
• Results 1 - 10 of about 232 for "space lift" geo. (0.20 seconds)
• Results 1 - 10 of about 133 for "space bridge" geo. (0.14 seconds)
• Results 1 - 10 of about 74 for "space ladder" geo. (0.33 seconds)
• Results 1 - 10 of about 67 for "star ladder" geo. (0.33 seconds)

And the order is much the same. (Note that people that beanstalk geo hits jack and the beanstalk a lot here. Also, 'star bridge' rates unusually highly- that's probably because there are several companies including 'Star Bridge' in their name, and geo itself is also a common name for products.)WolfKeeper 22:41, 14 January 2006 (UTC)

Decision: space elevator, beanstalk, space bridge, space lift, space ladder, star ladder WolfKeeper 22:46, 14 January 2006 (UTC)

Hope you don't mind, I added "orbital tether" to your results above. It didn't rank very highly, though, so it's looking like not the best sort of title. In fact, it's looking like "space elevator" is indeed the correct title for a ground-to-orbit tether as far as Wikipedia is concerned. This now moves my dilemma to coming up with a new name for the generic ground-to-orbit elevator, so that the intro of this current article can be split off to it. I wouldn't want to use Space elevator (disambiguation) because disambig pages generally don't contain article-like information in them - they're supposed to be ignored wherever possible. Hm. Bryan 23:05, 14 January 2006 (UTC)

Actually, "orbital tether" seems to be the second most popular term, ahead of 'beanstalk'; but it's not clear that it means the same thing as beanstalk- an orbital tether can be a bolus or a rotovator or whatever. Incidentally, I get very slightly different results, I'm using google.co.uk; that might have something to do with it.WolfKeeper 23:23, 14 January 2006 (UTC)

I tried "geosynchronous orbital tether" but although google initially looked incredibly promising, the only hits I found on this were actually the wikipedia mentions of it!!! (Try it and see- click to the end of the matches!)WolfKeeper 23:32, 14 January 2006 (UTC)

Hrmph. Which means that in accordance with our manual of style preference for the "most common title", the orbital tether variant of space elevator should be under the title "space elevator". Leaving no obvious place to put the stuff from the beginning of the article overviewing the whole concept of running elevator cars up a generic really tall structure. Since "space lift" appears to be not very common at all, perhaps I could hijack that title for this purpose? Bryan 01:36, 16 January 2006 (UTC)

Sabotage

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

Conservation of energy

Could someone please explain to me why this sort of device doesn't violate the conservation of energy? Why wouldn't a climber, pulling down on the tether, force the satellite into a lower (faster) orbit, thus breaking the geosyncracy? i.e. Where does the potential energy a climber gets while climbing come from? —The preceding unsigned comment was added by 66.240.10.170 (talk • contribs) .

The potential energy comes out of the rotational energy of the Earth itself - when an elevator car climbs the cable Earth's rotation is very very slightly slowed down, like the spinning figure skater who spreads her arms out. The first paragraph of Space elevator#Launching into outer space describes how this comes about, the key point is that a space elevator's center of gravity is actually slightly above geosynchronous orbit and therefore there's tension in the cable keeping it vertical. Bryan 01:36, 16 January 2006 (UTC)

Okay, I now understand that, but what about Newton's 3rd law? You pull yourself up a rope, the rope is pulled down by you. This will pull the counterweight down, yes? Why doesn't it "want" to be pulled into a lower, faster orbit?66.240.10.170 00:06, 18 January 2006 (UTC)

The starter ribbon pulls up on the Earth with a force of about one ton. Starting a climber up the ribbon reduces the pull on the Earth by the weight of the climber plus a bit more while the acceleration of the climber is occuring. The extra tension above the climber stretches the ribbon and the ribbon stretch tension goes up the ribbon at the speed of sound of the ribbon. The climber is most of the way to GEO altitude by the time the stretch tension reaches the counter weight and the counter weight starts to move toward Earth. Typically several other things have happened by this time so the counter weight decends very little. A large decent of the counter weight endangers the entire space elevator, so it is necessary to be sure the decent will be small before lanching a climber. Neil

Since the tether's center of mass is above geosynchronous orbit there's centrifugal force constantly pulling upward on the cable. As long as the force being exerted by the rising elevator is less than this centrifugal force, the elevator won't get pulled down. Perhaps imagine the elevator being supported by an enormous balloon, as long as you don't add more downward force to the balloon's tether than the upward force of its buoyancy it stays in place. As for Newton's 3rd, perhaps it will help to consider the entire planet Earth to be the reaction mass, like it is for a car accelerating horizontally on a road. Bryan 01:09, 18 January 2006 (UTC)

I don't know. The Earth isn't getting tugged at when someone pulls down on the rope. The climber exerts an outward radial force on itself, there must be an inward radial force exerted on the tether it's touching. Maybe the problem is I'm trying to put this all into an inertial reference frame. We could use the surface of the Earth as the reference frame instead. In which case, I suppose there'll be this vector field for centrifugal force which is altitude dependent, and we're putting something up where the force is stronger, like an anchor, and then pulling ourselves to it. Still, though, before we pull ourselves up, the counterweight is in equilibrium (centrifugal force, tension and gravity), so we increase tension, we throw it out of equilibrium. I'm still missing something.66.240.10.170 23:44, 18 January 2006 (UTC)Joel

When the car climbs, the elevator cable is no longer vertical, it leans slightly because the car is being accelerated slightly as it climbs. At the ground it would be going at 1600 km/h with the rotation of the Earth. When it reaches GEO it is going much faster (~10,000 km/h). So it is accelerating the whole time it is climbing. So the car pulls the cable a degree or two off vertical and the attachment point has to hold the cable in position, and that tugs on the Earth and minutely slows it down.WolfKeeper 00:34, 19 January 2006 (UTC)

And another thought occurs: if the center of gravity is in a higher-than-geosynchronous orbit, it's period will be longer, the counterweight will keep wanting to slow down while the tether drags it along so the cable won't keep vertical.66.240.10.170 23:44, 18 January 2006 (UTC)Joel

The elevator isn't in orbit. It's firmly attached to the ground. If you whirl a stone on a piece of rope does it always want to slow down? No, it doesn't (ignoring wind resistance, which anyway doesn't apply with the elevator since the air rotates with the Earth, that's why you're not sitting in a 1600km/h hurricane!)WolfKeeper 00:34, 19 January 2006 (UTC)

No, no. This is the source of our confusion. I'm not talking about the horizontal component of acceleration and velocity; that's fine. I'm concerned with the Newton's 3rd reaction force to the y-component of force, as it relates to the centrifugal force holding the counterweight up, the tension keeping its motion in a circle and the weight of the counterweight itself.66.240.10.170 04:44, 19 January 2006 (UTC)Joel

With respect to Newton's Third Law - think of it this way. You - the rope puller - are exerting a downward force on the rope that is less than the upward centrifigul force. An analogy (I hate those) would be if you're pulling on a rope that is bolted to the cieling. You could in theory apply enough force to tear the bolts from the mounts and bring the mess down onto your head. In practice you won't. Unless the guys who installed the bolts did shoddy work. I may have not understood the thrust (pun) of your problem ... Bdunbar 17:11, 23 January 2006 (UTC)

The rope to ceiling analogy has a self-adjusting force on the top of the rope. You increase the force pulling down, the rope is being pulled tighter at the top. Suppose you instead have a very buoyant hot-air balloon, tethered to the ground, and you're climbing the rope to get to it. The balloon and the space elevator have upward forces independent of their loads, which is why I can't seen an equilibrium situation if it's inequilibrium prior to the climbing. The climber causes the tension to increase beyond what the equilibrium tension was. Thus increased tension => lower orbit => less centrifugal force. Every time a climber goes up, the centrifugal force will lessen. You'll need some sort of rocket boost to make up the lost altitude. Unless we're saying that the tension below the climber decreases, but the tension above it stays the same, supplmented by the climber's weight. Then everything would stay in equilibrium.67.92.28.66 18:59, 23 January 2006 (UTC)Joel

I'm not able to explain it then - my fault I assure you. If I may - this is a great place to chat up the details of the Space Elevator article, but a poor one to discuss stuff like this. If I may suggest the Space Elevator group at Yahoo or the Liftport Group's Forum at http://www.liftport.com/forums ? The Forum is owned and operated by Liftport but we utilize a hands off approach for discussion there. Bdunbar 04:02, 24 January 2006 (UTC)

Seems obvious to me, and I've not done science since college. The center of gravity is above the middle of the cable, thus keeping the cable tense. So consider the analogy of a hot air balloon attached to the ground with a rope. Someone climbs the rope, the balloon is pulled down slightly, but when the climber reaches the top of the rope, ie the balloon, the balloon will rise again, regaining it's original altitude. Does that make sense? Kind regards, Roger Duprat

Balloons?

The strength of the tether is marginal, particularly in the lowest section. How much benefit could be had from supporting some of that lower section on balloons? --Midgley 22:44, 21 January 2006 (UTC)

Well, the average weight of the cable is under 1kg/km (lower particularly near the earth). A balloon might be able to go up maybe 30km or so I guess. So you'd only be saving 30km worth of cable worth of payload- about ~30kgs.WolfKeeper 23:46, 21 January 2006 (UTC)

Actually, Midgley has a point. Since the centre of gravity of the entire cable must extend beyond geosynchronous orbit, supporting the lower few kilometres by alternative means could drastically reduce the required length of cable. The lower few kilometres effectively weigh the most, and this downward force must be negated by an upward centripetal force. The force of gravity drops of with the square of the distance, while the centripetal force increases linearly.

Airships can travel to a height of up to around 20 kilometres, which means that the lower 20 kilometres could be eliminated, and a great deal more could be eliminated from the top part of the system.

All of this assumes a stable system though, I haven't thought about the system in operation, shuttling payloads and the like. A stable system could be realised using a reduced amount of cable. -- Ec5618 02:41, 22 January 2006 (UTC)

But how do you support it with balloons without overly complicating things? You'll have to find a way to attach the balloons to the tether without interfering with the climbers. You'll have to find a way to keep the balloon away from the tether at other than the connection point. You'll have to find a way to resupply the balloon with bouyancy (heat or lighter-than-air gas) that leaks out. It seems like the counterweight is the easiest way to support the tether. Val42 04:07, 22 January 2006 (UTC)

Objects are heaviest near the surface of the Earth. Using supports for the lower 20 kilometres would mean that the cable would not need to be quite so long, and wouldn't need to be quite as strong. The lower 20 kilomters of payload and cable would be supported, which means that the cable needn't support that mass.

Attaching balloons of airships is an added complication though. They would probably need to be detachable for maintenance and the like. Perhaps remote controled airships would fit; they could take turns holding evrything up. Whether the elimination of hundreds of kilometres of cable is worth such complication is another matter. -- Ec5618 15:32, 22 January 2006 (UTC)

I had not considered removing the bottom bit of cable or the physical connection to the ground/sea, just hanging it off er, well, a skyhook! It seems to me that the piece of cable one eliminates is the thickest piece - albeit it is not heavy, it is certainly massy, and reducing the mass budget to geostationary orbit seems to me arguably worth counting the pennies for. it also reduces the length of free cable, which must affect (I suspect trivially and non-usefully, but again, when doing things on a shoestring every little bit helps). I am just going to wave my arms a bit and assert that the problems of attaching the balloons to the cable are mere detail - one thought is that the lifting structure might be quite tall, and have a tunnel through it. The climbers for the main section would start there, and while they would presumably be starting on a cable even marginally thiiner than they would be at sea level, the transport system to the suggested blob need not be either a the same or b single. Given the continuing connection to the ground or sea, can I leave the problem of getting new gas up to the balloon from which depends the transport structure and a number of hefty tethers (guy ropes not Tethers) unanswered? In another interesting bit of technology proposed, and very much in the blue skies phase at present, there has been a serious suggestion that one can fly a windmill into the jet stream, and return the power down the tethers to the ground and the national grid. Most ideas that I have have been had by other people, but I have not seen that one. This suggests either it is slightly clever, or the numbers simply don't work. But I thought it might amuse the panel. Midgley 18:56, 16 March 2006 (UTC)

A lot of people talking on this page seem a bit confused - even I had to think about it somewhat before I realised what's actually going on. A space elevator is first and foremost a satellite in geostationary orbit. Thus its centre of mass is in that orbit. The forces on the cable extending down to the Earth, and up to any counterweight, are tidal in nature. Consequently they are greatest near to the centre of mass, and that's where the cable is thicikest. In principle the elevator doesn't need to be connected to the earth at all, and should exert no force on Earth. In this case, manoeuvering the elevator eg to avoid satellites is accomplised by rocket thrusters mounted on the elevator itself.

Thus it is wrong to speak of 'supporting' the cable by balloons. If one, for example, terminates the cable at 20km altitude, the elevator will still function provided the payload can be got to the base. Balloons or airships could accomplish this, but a better option might be a tower.

Also, it may be worth mentionning of the possibility of using some sort of funicular system, or regenerative braking, to gain energy from descending loads. It's likely a space elevator _would_ be used for descent, since it would eliminate the heating problems associated with standard reentry. 128.232.250.254 14:15, 23 May 2006 (UTC)

---

I would not think of a balloon just as a means of supporting the cable, I would make it a transfer station, a hotel, an observation tower, a radio repeater and make money out of it, well, at least, cover its operating costs... whatever. People might not care to spend several days (and lots of money) to get to geosynchronous orbit, but many wouldn't mind spending some time, hours or a few days, watching the Earth from above, and specially the trip up and down.

A balloon up there would allow for two separate models of climbers, one from the balloon to the ground and one for the rest of the trip, one atmospheric, the other not. The first would be cheaper (good for bringing tourists to the balloon) the other more expensive, since it has to deal with vacuum and several days of travel.

Moreover, the balloon would allow for two different propulsion methods. Cars in the lower segment would be plain cablecars moved around by a continuous tape. Actually, in this lower segment, the cars might not even use the main cable at all, they would all just grip the moving cable. The taper of the cable, mentioned elsewhere as a problem to this propulsion mechanism for the full trip, is not a problem in such a short length.

The cars above would still use power beams, with an added advantage: there is less atmosphere to dissipate its energy. In this sense, the higher up the balloon can be, the better to avoid as much of the atmosphere as possible (and to give tourists to the balloon the better view).

Also, a hot air balloon big enough is self buoyant, the sun can heat it enough so that it just stays afloat without any fuel or need to replenish helium. Actually, leaks become a minor maintenance problem, not a catastrophe. I still remember reading an article in the IEEE Spectrum magazine about that around 30 years ago (yes, it really impressed me). Based on then current materials a 400m diameter balloon would be self supporting, the larger you made it, the more the payload it could carry, a mile wide balloon could hold 400 tons or thereabouts. Building it and launching it was a big problem then, but not if you have an elevator.

The balloon at that height would also provide a better anchor since several cables from separate ground anchors could converge in it, thus sparing the upper cable from most atmospheric turbulence. --DevaSatyam 09:17, 1 September 2006 (UTC) wolfkeeper gave a good answer. A 30 kilometer altitude balloon supported platform increases the pay load by about 30 kilograms = 0.03 meteric tons. The platform is largely untested, humans would need a space suit at 30 kilometers. The climbers could climb the hold down ribbons for the platform, but it would be nesesatry to transfer the climber to the up ribbon at the platform. In theory robots can be designed to make that transfer, but that technology is also largely untested. The flipping of the ribbon around low earth orbit satelites and space junk is more difficult with the ribbon anchored at a platform instead of an anchor ship. Neil

Science Fiction

Sorry for not being very constructive, but the whole article is a horrible collection of heresay and speculation. The space elevator concept is still largely science fiction. Th article leaves the impression that space elevators will be operational 2018, and if not shortly after.

I acknowledge that space elevators are theoretically sound concepts, but so are generation ships, dysonspheres and cryonic conservation of live humans. The engineering challenges are *vastly* beyond reach of current technology in a number of areas.

You'd think so, wouldn't you? WolfKeeper 23:11, 8 February 2006 (UTC)

The first two paragraphs of the article are really good, no reason for critic here. But then follows a very large list of ideas and concepts concluded by a simplistic speculation why the problems of that approach can be overcome with no substantial evidence for any solution.

I think that the article should be substantially reduced in size, expelling the several wild speculations, especially about the future state of science.

Some examples:

"The primary power methods (laser and microwave power beaming) have significant problems with both efficiency and heat dissipation on both sides, although with optimistic numbers for future technologies, they are feasible."

What reasons exist to believe in an efficiency improvement in power beaming? This section is optimistic without reason.

The issue is to do with the solar panels heating up, and losing efficiency, mainly due to insolation (bizarrely enough). Ways to handle this issue are being considered; and it's not considered to be a hard problem.WolfKeeper 23:11, 8 February 2006 (UTC)

"For higher velocities, the cargo can be electromagnetically accelerated, or ..."

This sentence asserts the possibility of building a *railgun* in *space*, another theoretically sound project with equally epic engineering problems. This section is plainly ignoring problems.

Careful here. No, it proposes to use electromagnetic acceleration; perhaps some sort of coilgun. Coilgun physics is closely related with particle accelerators. Last time I checked, those work fine.WolfKeeper 23:11, 8 February 2006 (UTC)

"He proposes that a single hair-like 20 short ton (18 metric ton) 'seed' cable be deployed in the traditional way, giving a very lightweight elevator with very little lifting capacity."

How is that supposed to happen? Is the cable to be unrolled from space?

Yes. That's easily done.WolfKeeper 23:11, 8 February 2006 (UTC)

What drags it down?

The effect is called 'tidal forces'. The gravity is stronger nearer the Earth, and the centrifugal forces are stronger further away. The net effect is stretching the cable directly towards and away from the Earth. The cable therefore self-deploys. This has been done on the Space Shuttle using a conductive tether as well as other flown experiments. It works.WolfKeeper 23:11, 8 February 2006 (UTC)

Should it be deployed in flight? At 10 km/s without tearing? This section is too unspecific.

Yes, of course it wouldn't tear, tethers have been deployed like that before. In the case of a space elevator the cable would have little or no horizontal speed at any point in the deployment anyway. I actually have no idea where you got 10km/s from.WolfKeeper 23:11, 8 February 2006 (UTC)

"Sabotage is a relatively unquantifiable problem. Elevators..."

The whole section contains commonplace knowledge about sabotage. It refers to no original source.

Well, instead of complaining, why don't you fix it? The examples you give could be corrected/improved with small changes and a little additional text. As near as I can tell, you raise some valid points, with the possible exception of the notion that the challenges are vastly beyond current technology; that's a vague word, and I'm not sure it's supported. Also your last point re. sabotage seems unimportant; the article is only saying "this is something that needs to be considered", and I don't see how an original source would be useful. KarlBunker 13:21, 5 February 2006 (UTC)

"He proposes that a single hair-like 20 short ton (18 metric ton) 'seed' cable be deployed in the traditional way, giving a very lightweight elevator with very little lifting capacity."

How is that supposed to happen? Is the cable to be unrolled from space? What drags it down? Should it be deployed in flight? At 10 km/s without tearing? This section is too unspecific.

But you also complained that the article should be substantially reduced in size, expelling the several wild speculations, especially about the future state of science. Going into details you want in this instance would take a few pages of explanation, and might be speculative. Would you be happy with links to off-Wikipedia sites? 64.215.193.254 21:58, 8 February 2006 (UTC)

i always thought and still think balloons will proof to be the solution.

I actually envision a lauching platform for space travel over a cable for a balloon station 20-30km high. transport up though could be with 1 or two stages of balloons on cable. I imagine stages or at least a special construct for the upper platform are neccesarry becus you dont want to loose to much He. Cables if any, would firstly lead to the balloon platform (that should be huge)

perhaps spacecrafts can be launched from (rocket)propulsed balloons upthere, wich would allow for a smaller platform.

Lofstrom Loop

Is there a space in the non-tether solutions for Lofstrom's idea to be mentioned? I rather like it.Midgley 18:59, 16 March 2006 (UTC)

I think the Space fountain article would be a better place for that, since it's closely related to the space fountain concept, but currently only minimally mentioned in that article. KarlBunker 19:12, 16 March 2006 (UTC)

Visibility

I was just wondering, how far one could see the elevator if such a thing would be constructed? —Preceding unsigned comment added by 212.149.214.123 (talk • contribs)

Depends on a number of factors, really. Time of day, how refractory the outer layer of the ribbon is, the ultimate dimensions, weather, angle of view, etc.

We think the ribbon - on the first generation SE - is going to be a meter wide (average) and paper thin. Depending on your angle you'll have a hard time seeing just the ribbon more than a kilometer away under optimal conditions. Bdunbar 21:30, 24 March 2006 (UTC)

But of course, there would be at least one time of day when the sun is just right and you'd be able to see the ribbon for hundreds of miles. Val42 17:57, 25 March 2006 (UTC)

I think it would oscillate and twist enough that there would be no one unique time and direction. Only a very small proportion of the ribbon is going to be within hundreds of miles of anything from which it might be seen - except the climbers... Midgley 16:09, 26 March 2006 (UTC)

It just occurred to me that from the right viewpoint, the ribbon would catch the light after the sun has set, so it would be lit up against a dark sky. That might make it visible for a huge distance--depending on this, that, and the other thing, of course. KarlBunker 16:16, 26 March 2006 (UTC)

Taper calculation wrong

At time of writing, the article used 5.294e10 m^2/s^2 as the factor in the taper ratio calculation. However, substituting values in to the equation ([1]) seems to give a value of 4.832e7 m^2/s^2.

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

magnetospheric braking?

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

Angular momentum, speed and cable lean

I removed this from the article:

There are two approaches to having a stable system:

# either the counterweight must be positioned to the west of the tether point on the Earth, and matter must be raised up to orbit at a constant rate for the whole lifetime of the space elevator, so that the cable hangs vertically from the counterweight (see diagram), and all the angular acceleration comes from the Earth

# or the angular momentum of the matter brought down from orbit to the Earth's surface must be exactly equal to the angular momentum of matter taken up into orbit at all times.

If neither of these approaches is followed, the orbital velocity of the counterweight will change with time, which leads to complex (and often unpredictable) motion of the counterweight around the tether point on the Earth. The second approach is the one which is most commonly suggested, usually using mass from the counterweight to compensate for matter lifted into geostationary orbit. Note that a temporary shift of the position of the counterweight just during the lifting process is not feasible, as all approaches which deliver a stable shift to the position of the counterweight during the lift of an object (changing the orbital phase of the counterweight, but keeping the orbit circular, and then changing it back) would require more rocket thrust applied to the counterweight than would be required for a conventional rocket launch of that object from Earth.

This is just wrong. As the payloads climb the counterweight moves around, but no propellant burn is ever needed. There are some issues due to lack of damping, but timing the payloads can damp out any oscillations that may build up.WolfKeeper 12:31, 12 June 2006 (UTC)

The elevator is like a swing hanging off the Earth. If you send a single payload up, you start it swinging; but if you time the next payload correctly the swing cancels out (the elevator has a natural resonance of about 10 hours I believe; so sending another payload up at the 5 hour mark cancels the swing from the first. Sending payloads more frequently than that damps it out even more. You have to control climb speeds and so forth- the coriolis force is proportional to climb speed, careful control of speeds can damp the cable out entirely.WolfKeeper 12:31, 12 June 2006 (UTC)

Microgravity

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

Nasa opening bids to build?

According to The Guardian [3], NASA will be inviting bids to build a space elevator, during this month (September 2006). If this is true, this is exciting news, however I didn't realise current technology is ready yet. The Guardian didn't state its sources for this report.

It is just a contest on some of the basic technologies, small-scale climbers, short sections of cables and so on. No, the technology is not ready for a full scale project. --DevaSatyam 16:38, 3 September 2006 (UTC)

Current event

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

Airplanes?

In the hazards, there's no mention of the possibility of airplanes or such to crash into space elevators... There should be, shouldn't there be?

Equation summary/description

The cable thickness equation is summarized as follows:

This equation gives a shape where the cable thickness initially increases rapidly in an exponential fashion, but slows at an altitude a few times the earth's radius, and then gradually becomes parallel when it finally reaches maximum thickness at geostationary orbit.

As a casual reader (me), the word "parallel" makes no sense. How can the cable thickness go from "increasing rapidly" to "slows" and then to "parallel?" Parallel to what? Please adjust. JM 216.165.146.161 07:28, 28 September 2006 (UTC)

"Centrifugal" Force

This is seriously disappointing how often the word centrifugal is used in this article, whereas centripetal is used only once. I have neither the time nor the degree of concern necessary to make the appropriate changes to this featured article, but let it be known that there is no such thing as centrifugal force. Look at the first bullet under centrifugal's article and you'll see the words "Pseudo or fictitious." Please, please, please, when talking about matters of science such as the space elevator use the term centripetal. And yes, I am aware of a device called a centrifuge, but it does not use centrifugal force, contrary to what the Wikipedia article may say. Wikipedia is not, after all, the sole responsiblity of the respectable scientific community. It uses centripetal force. The word 'ain't' made it into the dictionary only by frequent batteries of misuse. Those of you responsible for Wikipedia's contents, please find it in your hearts not to let the whole centrifugal situation get any worse than it has gotten.--Spawnofbusey 23:32, 16 October 2006 (UTC)

I noticed this as well, and fixed it in one place, but someone reverted the to the earlier version. Centrifugal force is an illusion caused by the laws of motion - centripetal force is real. I'm planning on fixing this sometime later this week. Phædrus

It's not really that's simple. The elevator is actually really pretty difficult to analyse in a non rotating frame where centripetal forces exist and centrifugal don't. The 'non existence' of centrifugal force is to some degree, just something they tell the newbies in physics lessons so that they get the right answer in exams, because they haven't grokked the difference between inertial and non inertial reference frames yet.WolfKeeper 04:08, 6 November 2006 (UTC)

However, if you are actually doing serious work in a rotating frame of reference, centrifugal force is real enough and nothing bad happens, and the maths gives precisely the right answers. In this article, the earth/elevator is a rotating frame of reference, and thus the centrifugal force appears and opposes the force of gravity. You can get rid of the force by calculating accelerations, and using the term 'centrifugal effect', which fewer people argue with, but nevertherless, you would still have a 'magic' acceleration that appears here since it's a non inertial frame. If you do start using 'centrifugal effect' you will pretty much have to remove the word force from everywhere in the article. It's really a can of worms you are trying to open here, and I cannot recommend against it strongly enough.WolfKeeper 04:08, 6 November 2006 (UTC)

And BTW you can't simply replace 'centrifugal' with 'centripetal'- the forces are in exactly opposite directions so the maths screws up.WolfKeeper 04:08, 6 November 2006 (UTC)

I'm with WolfKeeper. Some people seem to think that because centrifugal force is a "pseudo" force, that means that the word and the concept are incorrect. They ain't. "Centrifugal force" is a simplification, but not a misrepresentation. It's a very "real" pseudo force. The point of this article is to make the concept of the space elevator understandable, and using this simplification is a great help in doing that. KarlBunker 11:15, 6 November 2006 (UTC)

In any case, centrifugal is used incorrectly in the place of centripetal in a few places, as in this part: "This is because a space elevator must be kept in tension, with greater centrifugal force pulling outward than gravitational force pulling inward," Centrifugal means towards center - Centripetal means away from center. In this case, at least, it should be centripetal. Phædrus 01:38, 7 November 2006 (UTC)

You might want to check your facts on that, I believe you have them switched around.WolfKeeper 09:42, 7 November 2006 (UTC)

Oh, dur. Sorry, got confused. Brain fart. Phædrus 01:20, 8 November 2006 (UTC)

I love this. Centrifugal force is useful in two areas: 1) upper level physics courses on central motion (e.g. writing a differential equation in terms of "r" and explaining why the hell the particle just doesn't fall into the center) and 2) heuristic and intuitive layman explanations for things like this. Both are perfectly legitimate. I mean if you really want to get postmodern... a force is anything causing an acceleration, but acceleration tacitly relies on your choice of interpretting space. Newton's laws even still hold with minor modification.--Loodog 19:58, 21 January 2007 (UTC)

Too Long!

Am I the only who thinks this article is far to long? When it gets to the point that editing gets slow it is well beyond what it ought to be. Nobody sits down and reads through all this. I would recommend that some sections were moved into their own articles and that there was a much shorter section about them here(as hs happened with Space elevator economics). Elentirmo 00:26, 14 December 2006 (UTC)

I think the Space elevator economics example is a bad one, since that article is both disputed and in need of cleanup. However, I agree that this article is a bit long and excessive at points. It might be better to try and cut out some of the less important information and tighten up the text before starting new articles about sub-topics within this article. Grant 19:29, 3 January 2007 (UTC)

The space elevator economics article came into existence after one editor who had a very strong POV on whether space elevators were practical added large amounts of detail to the article in support of it and other editors started adding "counter-arguments" neutralizing it. It's not surprising that the end result still bears the scars of that dispute. :) I suspect splitting stuff out purely because of size concerns would have a cleaner result. Bryan 20:37, 21 January 2007 (UTC)

References

Reference #16 says it's a 404 error at the location it was originally found. However I found it here, should I update the link even though it's not on a NASA website? Grant 19:18, 3 January 2007 (UTC)

If it's the same source document I don't see any reason why not. A book is the same book no matter which library it's found in. Bryan 20:38, 21 January 2007 (UTC)

Article organization still has a big structural problem

I wandered away from this article for a while to do other things but I think a major problem I raised in #About this word 'Plausible' is still unresolved. The intro paragraphs for this article talk about how all sorts of structures that reach from ground to space fall under the classification "space elevator", and then there's an "orbital tether" header and everything after that reads like a separate article on just orbital tethers. Basically, there are two separate articles on two different topics that are spliced together in one page. My proposal before was to split off the orbital tether section into its own article (orbital tether), leaving space elevator as a general overview of the various concepts, and although objections was raised they were very nonspecific as to what was wrong with the idea. Does anyone have any other solutions to suggest, or specific details as to why my proposed solution is bad? Bryan 20:13, 14 January 2006 (UTC)

I more or less did this once already, and people reverted it. I didn't call it orbital tether I called it 'beanstalk'; but otherwise that's what I did. I think there's enough people that think that space elevator == beanstalk/orbital tether that it won't fly.

Besides who says that space elevator really isn't just a beanstalk? Is a space fountain actually a space elevator? Is a space elevator a structure that reaches space or is it just another name for a beanstalk? Near as I can tell wikipedia has a significant chance to define what 'space elevator' exactly means here. It's not totally clear.WolfKeeper 21:03, 14 January 2006 (UTC)

Well, we shouldn't decide what these things should be called - that'd be original research. All I'm proposing here is that this article should be split because it's two articles smooshed together, what we ultimately call these things is ambiguous and we'll need all sorts of "also known as"es in the opening line. Bryan 22:37, 14 January 2006 (UTC)

Shouldn't the history part head the article ? --Anne97432 06:59, 27 April 2007 (UTC)

The terms "bean stalk" and "space elevator"[4][5] are generally used interchangeably in the engineering literature to refer to an anchored cable or tower extending from Earth/ground to Geosynchronous Earth Orbit and a bit beyond with the counterweight. "Fountain" is a special elevator, the structure rides a high speed momentum exchange medium (typically iron/steel loops) rather than supporting itself. An orbital/space tether[6] (also a standard term easily citable in the engineering literature) is a completely different animal from an engineering and operations standpoint. Merging/leaving these two in the same article makes about as much sense as putting sea ferries in with bridges. The key difference is that one rides/climbs the elevator/beanstalk/tower like an elevator. The space tether (skyhook) tosses the cargo on vector planned. In my opinion Wikipedia would be better off with a couple of appropriate stubs or half articles ... assuming they could avoid deletion while they were improved. Anybody interested could start a discussion of engineering details or approaches at www.wikiversity.org Perhaps a decent summary of various engineering approaches would eventually result that could be transwikiied/merge back to Wikipedia. Lazyquasar 02:01, 25 September 2007 (UTC)

Why use power to lift?

Cut the teather... Let the lift fall to space. No energy needed for it to reach space other than the couterweight! Construct a Lift Station in space that controlls the teather so the shipment and the couterweight do not fall into space.

                                   O --- Lifting Couterweight
                                   |
                                   | --- Lifting Cable
                                   |
                             -------------
                             |           |  ------ Lifting Station 
                             -------------
                              |    |    |
                              |    |    |   ------ Station Teathers
                              |    |    |
                              |    |    |
                              | (=====) |   ------ Cargo
                              |         |
                              |         |
                    --------------------------------   

Lifting Station controlls rate of Lifting Cable passed through it. Multiple teathers attach Lifting Station to the ground, station is and acts like its own couterweight. Guides can be attached to station teathers to controll cargo as it heads toward space. In the event of the lifting cable breaking the cargo would not fall to space or earth by safety devices that can be placed in these guides. Station would also be able to assist in getting the cargo going in the direction it needs to be going after it reaches space. —The preceding unsigned comment was added by 71.8.208.173 (talk • contribs) 19:46 UTC, 5 June 2006.

That's an interesting idea, but here isn't the place to discuss it. This talk page is for helping to put together the encyclopedia article, not for general chat about space elevators. If you can provide a reference for that plan, then let us know and we'll add it to the article. If it's more your idea and you don't understand why it isn't done that way then you could ask the reference desk, or if it's your idea and you want to publish your ideas, then you need a web host or a scientific magazine, depending on your level of expertise. --HughCharlesParker (talk - contribs) 19:15, 5 June 2006 (UTC)

Maybe there should be an article for this kind of idea(s)? I mean... wikipedia is a tool for the amassing and pursuit of knowledge, no? "Space Travel Theories" or something. Degen

dont worry about it Degen theres alot of unimaginative white coats on here who's only pleasure is lots of numbers. —The preceding unsigned comment was added by 82.36.32.73 (talk • contribs) 00:55, 4 October 2006.

It's not that I'm only interested in numbers. I'm here to further the wikipedia project, as we all are, and wikipedia is about building an encyclopedia. Two useful pages to read if you want to gain some insight into how the project works are our policy page and our page about what wikipedia isn't. Particularly, wikipedia isn't for original research - material we use must be verifiable by citing a source. --HughCharlesParker (talk - contribs) 09:18, 16 May 2007 (UTC)

Discussion of engineering details or concepts are welcome at http://en.wikiversity.org/wiki/School:Engineering Any applicable information or summaries are easily ported back to Wikipedia as both currently use the GFDL. Lazyquasar 02:06, 25 September 2007 (UTC)

Carbon nanotubes

I was at a talk about carbon nanotubes a while ago and the speaker mentioned that they would be a likely material to be used if a space elevator was ever built. This is already mentioned in the article. Can anyone back this up with a published source? savidan^{(talk) (e@)} 17:09, 14 June 2006 (UTC)

Well, who was the speaker at your talk, and was the lecture recorded? We could use that. siafu 19:14, 14 June 2006 (UTC)

No, they would not be a likely material. It just makes no sense at all, somebody just like s the sound of "carbon nanotubes". UHM (Ultra-High-Modulus) Carbon Fiber is at least two orders of magnitude more reasonable as a material for the cable, since it's component monocrystalline domains are two orders of magnitude longer. It's still ridiculous, but at least it pretends to make sense, where as the "carbon nanotube" idea only *sounds* good. I tested short lengths (~ 1 cm) of carbon fiber with a modulus of 130Mpsi to failure at nearly 1% strain, or 1.2 million psi. Still you couldn't make a space elevator cable out of it...

—Preceding unsigned comment added by 131.215.115.31 (talk) 15:13, 10 July 2007

Center of Mass?

I believe the diagram is incorrect. It labels the point on the cable which intersects the imaginary line of "geosynchronous orbit" as "center of mass". But wouldn't the center of mass, by necessity, be at an altitude higher than geosynchronous orbit? I would think that no matter how heavy the counterweight is, if the center of mass of the entire system (cable + counterweight + any climbers) falls below the height of geosynchronous orbit, then the entire thing would collapse. Ravenswood 17:12, 21 July 2006 (UTC)

I don't think it would collapse. By conservation of angular momentum, if the COM fell below GEO, it would increase in angular velocity relative to the Earth, which would greatly incrase the tension on the cable and potentially sever it. siafu 17:27, 21 July 2006 (UTC)

Assuming it didn't snap, it would increase the angular velocity for a while- the cable would swing eastwards until the tether point slowed and then stopped it. At that point the cable would begin to fall more. It would then swing backwards the other way, and then fall more, eventually it would end up at ground level or burn up in the atmosphere, or a mixture..WolfKeeper 05:22, 2 September 2006 (UTC)

Odd orbital mechanics... The centre of mass will be sufficiently above the geostationary orbit to provide the tension in the cable. If the tension is small, and the mass is large (both reasonable assumptions) then the equipment needed to measure the difference in altitude may be more like a microscope than a ruler.

The question was what would happen if the centre of mass did go below Geo though. I still think if it was modestly below, it would rock back and forth a few times. However as it starts to fall, coriolis force kicks in and pushes it to the East, and it ends up wrapping itself around the Earth/burning up.WolfKeeper 16:43, 2 September 2006 (UTC)

In considering the mechanics, I think one has to avoid saying "If it falls below..." becuase there will be a reason why it is depressed - an applied force. WHen the centre of mass descends, it speeds up, potential energy being converted to kinetic. It won't swing back and forth and drop on teh floor. Midgley 16:07, 2 September 2006 (UTC)

The thing is that the length of the cable is roughly constant, so if it rocked back and forwards the altitude varies depending on the angle from the vertical. If it was to move far enough (and there are a number of drivers, such as tidal forces, and coriolis force due to climbers) it could in principle fall over.WolfKeeper 16:43, 2 September 2006 (UTC)

The diagram is incorrect, and most of the language involving the center of mass is as well. The center of mass is nowhere near GEO. It is not expected to, because different parts of the structure experience widely different gravitational and centrifugal acceleration (in the rotating frame). The gravitational acceleration near the surface is much greater than the centrifugal acceleration beyond GEO, meaning the part of the elevator beyond GEO altitude is much more massive than the part below. If you don't believe me, take a close look at the Cable Taper Plot. What needs to balance on both sides of GEO altitude are the forces, not the mass, and less acceleration means more mass. It does not matter, though, because center of mass is not a useful concept for extended objects in an inhomogeneous field anyway. To say "the center of mass is in geostationary orbit" is plain wrong. If I get some consensus, I will edit the text, but I do not know how to edit the diagram. Andreas 20:00, 13 June 2007 (UTC)

Pretzel logic

The article currently contains the following paragraph:

A possible complication not mentioned in most of the literature is the potential 'pretzel-effect' of a carbon nanotube ribbon which would, without wind mitigation, ultimately twist into a pretzel shape in the areas of the ribbon exposed to the atmosphere. The added tensile stress from these forces could break the ribbon and it admits of no simple solution. If the constant minimum load tension in the ribbon is sufficient (some have suggested 20 tons) such twisting may be mitigated by this tension alone. A cylindrical, cable shape eliminates this concern entirely as the twisting need only be mitigated at the end points.

I had to read this three times before I understood what it was trying to say, and that only because the vision of a paper streamer in the wind suddenly popped in my mind. This is screaming for a visual illustration... linas 04:49, 11 December 2006 (UTC)

Linas, if you understand what this is trying to say, you're doing better than I am. To my thinking, a "pretzel shape" is an overhand knot, and there's no way that wind could "twist" a ribbon cable into that shape. I think this passage needs rewriting. KarlBunker 11:55, 14 December 2006 (UTC)

[Later] Okay, I guess I should have looked at the article for pretzel, or perhaps an actual pretzel. A pretzel twist isn't an overhand knot and doesn't require that one end be free, so it could happen to a wind-blown cable. Still, this could use some better description; maybe "twisted into a pretzel-like loop"? KarlBunker 14:44, 14 December 2006 (UTC)

This paragraph makes no sense whatsoever. It has no sources, and should be deleted.

In fact, I think I will go ahead and do so. Andreas 02:58, 13 June 2007 (UTC)

Good move, especially since "wind mitigation" is discussed in almost source. siafu 03:13, 13 June 2007 (UTC)

Insignificant Slowing of the Earth

How can the slowing of the earth caused by the existence of the lift only 'insignigicantly slow' the Earth's rotation? Surely any slowing of it's rotation is a very bad thing and would need some form of countermeasure? The fact that this topic was skimmed over in the wiki gave me cause for concern. 129.11.76.215 09:04, 1 March 2007 (UTC)MrLaister

The same way that whenever you walk towards the west the earth is insignificantly slowed (and insignificantly sped up when you walk to the east). The great disparity of mass of the earth versus your body (or indeed a space elevator and payload) means that the actual slowing experienced is so infinitesimal as to not warrant worry, but does deserve a breif entry into the physics section of the Space Elevator wiki. Also, presumably an operational space elevator would have mass coming down as well as going up, so there's your countermeasure. ABVS 01:58, 3 March 2007 (UTC)

Or it may be the other way around - east slows, west speeds up... sun rises in east.. earth rotates to east... yes I think I was wrong the first time.ABVS 01:10, 4 March 2007 (UTC)

The angular momentum of the Earth is: 7.06 x 10^33kg m^2/s[7][8]. The angular momentum of an object weighing 1000 kg (1 tonne) in Geosynchronous orbit is 42,164,000m[9] * 3071 m/s * 1000 = 1.296^14 km m^2/s. So to add 1 second to a year we would have to decrease the angular momentum of the Earth by a fraction of 1/(365.25*24*3600) = 1/31557600. Multiply that by the angular momentum of the Earth and divide by the angular momentum of the object and we get 1.726 e 12. In other words you would have to launch a million, million tonnes into Geosynchronous orbit to slow the rotation rate by 1 second per year (if I haven't messed up my arithmetic.) But even if we did that, the normal variation of the rotation of the earth is about 1 second a year anyway (see leap second), due to weather and other effects, so nothing bad would happen(!) Hope this helps.WolfKeeper 03:23, 3 March 2007 (UTC)

Any English info on the hanging tether idea?

Like the title says, I'm wondering if there is any information on the hanging tether idea. It's basically the same idea as the normal elevator, but is only 4K long (with COM at 2km), and the Earth end of the cable has a sky-hook/platform for rockets to transfer cargo to the elevator. I understand that it's being developed for the next X-prize, but I only have Japanese language sources on it so I don't want to add it to the article. Anyone know anything about it? -- Bakarocket 17:01, 6 March 2007 (UTC)

The idea was discussed extensively by Robert Zubrin in an article in Islands in the Sky: Bold New Ideas for Colonizing Space (ISBN 0-471-13561-5). I don't know anything about it being part of the next X-prize, though. siafu 17:57, 6 March 2007 (UTC)

Should it be added into the article as an alternate version in 4.3, or is there another article already available? For the X-Prize part, I just did an interview on a guy involved with the project, which is why I came here looking for some back-up. It would be intellectually dishonest for me to use my own print article as a source though, which is why I was looking for other English sources. I've never touched this article, so I thought I'd ask the regulars first. -- Bakarocket 18:30, 6 March 2007 (UTC)

Where is your article published? siafu 16:43, 10 March 2007 (UTC)

It won't be out until next month, and it'll be in an English newspaper in Japan. I'm not going to add anything until I can source it from Zubrin's piece, though. I'd feel dirty.-- Bakarocket 05:04, 11 March 2007 (UTC)

similar applications?

I'm intrigued by the idea of a space elevator. But surely there are similar applications that would cost far less to implement and should be mentioned in this article. Off the cusp, I can imagine a space pump for ridding the world of gaseous, solid, and nuclear waste. We could pipe all our waste to a network of regional pipes that could then be ejected through a central space pump into outer space. Obviously, the harmful waste would have to be ejected with a sun-bound trajectory so it would be incinerated. Bet that would put a significant dent in our polution and waste problems. Moto 02:31, 10 March 2007 (UTC)—The preceding unsigned comment was added by Teeroy (talk • contribs) 02:21, 10 March 2007 (UTC).

SOrry, what? Are you suggesting a new form of transport?--Bakarocket 12:00, 10 March 2007 (UTC)

How is that different to a space elevator? Wouldn't that in fact be orders of magnitude more difficult, what with having to build a pipe instead of a cable, not to mention designing a pump that could handle a head of several thousand kilometres...ABVS 00:10, 11 March 2007 (UTC)

It's different in that Space Elevators are being researched and Space Garbage Disposals aren't. --Bakarocket 05:04, 11 March 2007 (UTC)

Poisson ratio and elongation?

Partly as a matter of interest and partly because maybe it should be added to the page, does anybody know how elongation and deformation from tension (and maybe even tidal forces) would affect the calculations? —The preceding unsigned comment was added by 207.112.60.14 (talk) 00:01, 29 March 2007 (UTC).

Given that the loading is purely axial, the poisson ratio is not so important as the cable taper can easily be designed to account for the stretching effects. According to our article on carbon nanotubes, the elastic modulus of the material is on the order of 1 TPa; just back-of-the-envelope assuming a length of 42,164 km (GEO), an average thickness of two meters (a convenient cross-sectional area of pi meters), and a loading at the "end" of ~70 MN (this one is just a guess), the total elongation would be about 940 m. This is about 0.0022% the entire length of the cable (i.e. the strain is 22E-6). This would affect the caculations only very slightly, but would be more important in calculating the oscillating behavior of the structure, which is much, much, more complicated. siafu 01:00, 29 March 2007 (UTC)

Ok, I looked into a little more. If you look at the Pearson article (reference number 7 i tihnk), on pg. 10 he has a discussion on elongation. When the tower stretches, more of it is passes geosynchronous orbit which, in turn, stretches it more. For a tensile strength/Young's modulus of .0482 he gives a stretch of 5%. Nanotubes have ~.06 which would give an even higher stretch. Unfortunatly I didn't see this mentioned in any of the other article so I'm not sure what the deal is. 207.112.60.14 04:08, 29 March 2007 (UTC)Yonni

You are right. The Young's modulus (1TPa) and required tension (50-60 GPa) fix the elongation at 5%-6%. The 0.0022% number above must be a mistake. Andreas 14:20, 13 June 2007 (UTC)

The calculation is right enough; it was a guess based on faulty data. siafu 14:26, 13 June 2007 (UTC)

Wouldn't The Counterweight change the earth's orbit and kill everyone

Anyone? —The preceding unsigned comment was added by 24.168.30.85 (talk) 01:25, 29 March 2007 (UTC).

No. siafu 01:45, 29 March 2007 (UTC)

Citation needed

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

• One rather recent discovery is that high wind speeds can flatten the elevator cable horizontally across the surface of the Earth perhaps a hundred kilometers. Surprisingly, the stress on the cable is not significantly increased (since the elevator is tens of thousands of kilometers long the percentage increase is tiny) and no major damage is predicted.

• It is also possible that a private entity (risks notwithstanding) could provide the financing — several large investment firms have stated interest in construction of the space elevator as a private endeavor.

A few comments on the article

Good article overall, but in reading through it I think that certain areas are in need of improvement. Firstly I thought there wasn't really enough explanation of why it would be preferable to build a Space elevator. The economics section has info on costs and all, but this is rather brief and comes towards the end of the article, I would think that explaining the perceived necessity of such a device would be one of the first things to state.

There were some things about the specifics of the engineering which I think need a lot more explaining, for one, is it proposed that the cable be a single thick wire or many tiny thin ones? It seems to be talked about at various points as if it could be either, so I think that needs more clarity.

Something quite important that I don't think was addressed at all (or at-least I couldn't see it) was the issue of how exactly the cable (or the whole structure) actually gets up into space in the first place. Are we to assume that the cable will be towed up by a rocket or something? If not that, then how?

Several times in the article it is mentioned that the "Counterweight", could be an asteroid or a space station. But these two things are very different aren't they? I mean in terms of mass, an asteroid probably weighs millions if not billions of tons, whereas a manmade space stations would be only a few hundred or thousand tons (unless some gargantuan station is proposed). So how can these to things be comparable? And what kind of actual weights will be involved?

Finally the article doesn't give much information on how the climbers are proposed to move. It is mentioned further down that Magnetic levitation might be used, but is that the norm, is that what they all propose? Or are there different plans, like just mechanical wheels, etc?

Well that's about all I can think of for now, I hope the article can be improved with some of these suggestions. --Hibernian 00:00, 13 June 2007 (UTC)

It's been a while since I posted this, so can no one provide any answers to the questions I was asking? I think it's needed, if not for myself, then for the article. --Hibernian 23:22, 14 July 2007 (UTC)

I am not an expert on the subject but seeing as no one else has adressed your questions I will try. I assume it will get into Space like the ISS, in pieces and assembled in space. An asteroid can be any size at all. For the third, you might want to read the source.10max01 23:31, 14 July 2007 (UTC)

The plan being put forward by Liftport involves the cable being sent into orbit before deployment, in pieces; the plan you find in many sci-fi/futurist sources involves snagging a small asteroid and building the cable out it. The former is rather more realistic.

The two types of counterweight are equivalent due to conservation of angular momentum. The "space station" type counterweight requires much more cable, placing the counterweight a distance of 4-5 times further out than geosynchronous orbit. A large mass, like an asteroid, could be located closer to GEO. Again, using an asteroid is much science fiction than realistic possibility, but they do come in many sizes as noted by 10max10.

Lastly, different types of climber propulsion have been proposed. The Tether Challenge, one of NASA's Centennial Challenges, involves coming up with an effective way propel climbers using beamed power. Magnetic levitation sounds nice, but is rather pie in the sky, as evidenced by the fact that none of the Tether Challenge robots have used it. More likely very large rollers or somesuch would provide propulsion. siafu 00:32, 15 July 2007 (UTC)

Your answer seems pretty adequate.10max01 00:37, 15 July 2007 (UTC)

Ok thanks for the responses. So is any of this going to be put into the article? As my main compliant was that the article didn't explain these things adequately. --Hibernian 02:42, 17 July 2007 (UTC)

86.137.107.103 19:18, 29 September 2007 (UTC)== Cable taper plot ==

The cable taper plot shows a wildly different area ratio at GEO to that quoted in the text for steel (about 1.8 versus about 10^14). What assumptions is the plot is making about the type of material used? Are these in any way reasonable? I think that this discrepancy needs to be explained in the article. Matt 13:06, 6 August 2007 (UTC).

Using a value of 2GPa for the tensile strength of steel and density of 8000kg/m3, the equation says that the area at geostationary orbit should be on the order of 10^80 (area at ground level of 1cm2). Unless my arithmetic's gone wrong, I think that the thickness at GEO for steel should be changed. Concerning the taper plot, the inverse strength-density scale isn't all that useful - most materials seem to have inverse strength density ratios of orders of magnitude lower than this, so the ratio Area/Ao would be orders of magnitude higher for most materials. Essentially, the cable taper plot is correct, but not particularly useful - if anyone knows how to extend it for other materials, that'd be very useful.

86.137.107.103 19:18, 29 September 2007 (UTC)

Towers

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

Helium Balloons.

I am aware of No Original Research, though I reckon that it must be the case that someone has already published what I am stating here, and hence that the information is citable. But, would strategically placing Helium Balloons at certain points along the tether aid the feasibility of creating the elevator? I believe that this might be so as the tension along certain points of the tether would be reduced via the use of such balloons (they would relieve the tension of the tether from under it's own weight at several strategic points along the tether). However, this is only something that could be done up to a height of about 20 miles up (the height to which most helium balloons will go. You might be able to squeeze out some more height using Hydrogen. It may even be possible to create several mile high rigid `floating structures' attached to helium/hydrogen balloons that could support the tether 30 miles up or so by attaching so structures to such balloons. Nevertheless, I remain pessimistic that the (600 mile?) barrier for fully fledged space access is traversible from such meagre heights (though, in actuality, this outlined approach might be more feasible than the space elevator AND overcome a significantly large proportion of the energy costs requires for getting into space).

If I have made an error in my reasoning, I would sure like to know.

Also, perhaps (solar powered?) magnetic sails (that force against the Earth's magnetic field) could be used to reduce the weight induced tension along several points of the tether? Perhaps more conventional thrust generation methods would relieve the tension allowable for a greater flexibility in material utilisation?

A general point could be that the space elevator doesn't really need to take up into space at all in order to be economically viable – it just needs to get us 10% of the way up (aren't most of the energy hurdles in relation to leaving the Earth's gravitational field used up in making the first small proportion of the distance?).

I have not done any calculations when making this post – though I do believe that the approximate figures given are unlikely to be terribly incorrect in principle at least.

ConcernedScientist 01:22, 30 June 2007 (UTC)

It's a reasonably good idea, but this isn't the place to discuss it.WolfKeeper 17:47, 14 July 2007 (UTC)

I concur. Though, with hindsight, I would refer the reader to Talk:Space elevator/Archive 6. Here, the balloon idea was already mentioned. I am not aware of any mention having been made concerning using high current conductors attached to the tether to induce a force due to the Earth's magnetic field (I know, the earth's magnetic field is probably only (0.3/16) Tesla's at any real appreciable distance from the surface - but it should still be feasible to generate a decent force capable of reducing tension within the tether so that carbon nanotube material isn't needed at all.

(Consider F=BIL, and a long superconductor on a moving air based platform to see that Carbon Nanotubes might not be absolutely necessary).

Anyhow, forgive my rambling, all of this is probably WP:NOR bound, so I'll stop making a mention of these ideas (though I doubt that they're Original Research as they are so obvious that someone must have posted them some time ago...).

ConcernedScientist 00:59, 15 July 2007 (UTC)

I believe balloons will not significantly improve the economics of the Earth/GSO cable configuration. Cable materials can be characterized by the length of a uniform cable that can just sustain itself against gravity without breaking, essentially l = (T/(g*rho)), if l is the characteristic length, T is breaking tension, g is acceleration of gravity, and rho is cable material density. For a tapered cable near the surface, the area must grow by a factor of e every time you go upwards by l. If I recall, l is on the order of 10 km for ordinary steel cable.

Unfortunately, the effective potential height of the Earth's gravitational potential well is about 5,500 km (again "if I recall"). So for steel we get an awful factor, of exp(5500/l) = exp(550) or so. This effective potential is the depth of the gravitational energy well of the Earth (which is just the radius -- about 6380 km for Earth -- for any spherical planet, since the 1/R^2 force's potential is -1/R) after taking into account the opposing centrifugal force, integrated from the surface to GSO. So, it reduces the problem from about 6380 km to ~5500 km, not a huge effect.

Near the surface, the gravitational acceleration is g ~ 9.82 m/s^2, so the potential height is essentially the same thing as the geometric height, 1 km per km. Thus what kills you is the region between the surface and 1 radius or so, where you have the bulk of the effective potential height that has to be overcome. Because the atmosphere is thin, scale height ~10 km, balloons won't work high enough (50 km is about their limit) to have much of an effect (just as shortening the cable by say, 50 km, so that the end dangles above the atmosphere, does not really help either).

The good news in the horrible exponential is that, IF you can find a material with a much better l, you can get a colossal reduction in the mass and a corresponding improvement in the economics. As far as I know, single-wall carbon nanotubes have the best l known to date, I believe the figure is over 1,000 km. Unfortunately, they are not yet available in quantity with uniform quality and sufficient length. I believe spinning such fibers into multi-strand yarns or cables is probably the way to go, but as far as I know it is still just an exciting possibility.

A comment here from someone in July 2007 attacked carbon nanotubes, but (while I am by no means an expert) the theoretical l numbers measured for some of them seem to make them the material of choice. I will try to provide better documentation from the literature as soon as I can, if it has not already been done by someone else. (Being new to this article I need to read it all carefully, and the discussion too.) Wwheaton (talk) 08:15, 18 December 2007 (UTC)

Image incorrect

I replaced the SVG diagram of the elevator with the original PNG one, because the SVG showed the elevator to go up from the north pole, which is nonsense. Many people don't intuitively understand why it has to go from the equator, because many don't understand the idea of an orbit. 79.120.55.7 07:01, 20 September 2007 (UTC)

I'm glad I wasn't the first person to catch this mistake. But it looks as though it's been reverted to the SVG. The caption mentions a geosynchronous orbit but the picture does not reflect it. I was so surprised I had to go back and check my physics ;) -Verdatum (talk) 18:21, 27 November 2007 (UTC)

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

Failed verification tag for Smitherman

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

Possible typo

"In an ideal cable, the actual strength of the cable at any given point would be no greater than the required strength at that point (plus a safety margin). "

Shouldn't it say less than?

It's correct this way, but perhaps not obvious. Strength in excess of the minimum comes at the cost of mass, and excess cable mass is a killer in a space elevator design. Keith Henson (talk) 14:45, 18 November 2007 (UTC)

Clearly the actual strength can't be less than the required strength at a given point! So taken together, "no greater than," and "not less than," means "equal to".

Missing discussion of technical problems

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