Talk:Space elevator/Archive 6

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Contents

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)