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Space Science

Lunar Space Elevator Instead? 340

Posted by michael from the think-big dept.
koa writes "We have all seen articles on building a Space Elevator on the earth, how about this article about experimenting with the Moon first since the technology we have available to us is sufficient, as the Moon's gravity is 1/6th that of Earth's (the cable weight would require less exotic materials such as carbon nano-tubes). One could make a very good argument for commercialization of Space if getting materials to and from the Moon's surface was vastly cheaper and easier."
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Lunar Space Elevator Instead? More

Lunar Space Elevator Instead?

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  • Interesting (Score:5, Funny)

    by Sv-Manowar ( 772313 ) on Saturday November 20, 2004 @08:08AM (#10874057) Homepage Journal
    This theory has been investigated in depth in a recent book, http://www.amazon.com/exec/obidos/ISBN=014032870X/ 002-2420335-1812868 [amazon.com]

  • The point? (Score:2, Insightful)

    by hfis ( 624045 )
    I thought the point of an elevator was to provide a launch platform removed from the restricitons of Earth's gravity and atmosphere. These don't exist on the moon, so what's the point?

    Waste of money IMO.
    • The point is that it would be easier to build it on the Moon, so we could concentrate on perfecting the technology (on a smaller scale). If we get it working on the Moon first, it'll be easier to do on Earth.

      • Re:The point? (Score:3, Informative)

        by jdray ( 645332 ) *
        Actually, per the article, the point would be to have a no-propultion way to get materials off the lunar surface and into an earth orbit where we can use them for construction.
    • Gravity doesn't exist on the moon?

    • Re:The point? (Score:2, Insightful)

      by cbreaker ( 561297 )
      I was wondering the same thing; the whole idea was to get people in orbit easily and much cheaper (well, once the initial costs are paid..)

      While the moon thing isn't a terrible idea it doesn't seem like it should be an "instead" but rather an "addition to."

      • Re:The point? (Score:2, Informative)

        by Englabenny ( 625607 )
        No, the idea has never really been to put people into space; there are too many problems with this. As noted in the article, the time of the travel and cosmic radiation is a large problem with human transport in elevators. Even more so in the earth case, where we have the van Allen radiation belts. With the elevator in place at the earth, we'd have a tremendous goods shipping facility. Human travel comes much later.

    • Re:The point? (Score:3, Insightful)

      by div_2n ( 525075 )
      I know this is /. and asking people to RTFA is a waste of effort, but just do it and you will have your answer. But since you won't, I will spoon feed you.

      The point of the space elevator is to lower the cost of getting things from the ground to space. Even on the moon, you have to use energy to get things off the ground. The moon has resources that could be utilized in space (or Earth). Instead of having to land spacecraft, risk the dangers and use fuel that you have to get from Earth, you can set up a

  • Lunar Space Elevator? (Score:5, Funny)

    by Anonymous Coward on Saturday November 20, 2004 @08:14AM (#10874087)
    Bah! The idea is pure lunacy.

  • Except.... (Score:3, Insightful)

    by Anonymous Coward on Saturday November 20, 2004 @08:14AM (#10874088)
    Earth is where all the people and materials are. Building a space elevator on the moon would be like building a superfreeway from one point on antarctica to another point on antarctica: pointless as there's noone around to use it, nor anything to transport over it.

    If you are going to just say "move people and materials from earth to the moon, then go from there" - you still have to escape Earth's gravity, which is the f'ing point of the earth-based space elevator to begin with.

    • Re:Except.... (Score:5, Insightful)

      by Garion Maki ( 791172 ) on Saturday November 20, 2004 @08:26AM (#10874122)
      unless...
      you build the expencive elevator on the moon and start up a few mining/refining outposts with self suporting habitats.
      once those are working good, you can start working on space stations/ships/habitats for a cheaper price, since most of the materials don't need to go past earth's gravity well, only the main part of human labor would need to come from earth.
      the big and expencive part of the materials could be cheaply inported from the moon, and in a later stage, when space travel has inproved, you could get that stuff from the asteriod belts etc.

      so even tho it might seem like a big and expencive thing to do, it might be verry usefull in the future.
      • And how technologically accessible is it to actually put something on the moon that would be worth building this? Look at the speed the Space Station is progressing with. Heck, even lifting materials and machine-power to assemble the elevator there would be a lot.

        We might actually be closer to building the elevatorhere than to establishing any sort of moon base in terms of technology. Not to mention that a working space elevator on earth would make the Moon a hell of a lot more accessible.
        • The US is willing to spend a lot of money on their military, the war in Iraq costs 150,000,000,000$. For that amount of money, I'm sure you could build a couple of elevators. The only reason we don't get of this rock is because we prefer fighting each other.

          On the positive side, this means that once we achieve world peace, a space elevator on the moon should be no big problem, only an exciting challenge. On the negative side, this means we might never be able to get there (has world peace ever existed in h

      • Re:Except.... (Score:3, Insightful)

        by Mr2cents ( 323101 )
        Indeed, soil is mainly SiO2, I don't think it's difficult to split it into Si and O2. With the silicium you could make solar cells (they are made in a vacuum so the moon is naturally suited for that), and the O2 can be used for breathing or as rocket fuel. The hydrogen is much lighter than the oxygen, so even if you would have to transport it from earth it would still be profitable. And instead of transporting the hydrogen, you might send hydrocarbons like methane, butane or octane. Then you get some carbon
      • "you build the expencive elevator on the moon and start up a few mining/refining outposts with self suporting habitats."

        Better yet just use remote controlled mining + refining equipment and then the people controlling them can sit nice and safe on Earth, and you don't have the massive cost of the self-supporting habitats.

    • Re:Except.... (Score:5, Insightful)

      by TFGeditor ( 737839 ) on Saturday November 20, 2004 @09:21AM (#10874299) Homepage
      "Earth is where all the people and materials are. Building a space elevator on the moon would be like building a superfreeway from one point on antarctica to another point on antarctica: pointless as there's noone around to use it, nor anything to transport over it."

      "Iinsightful" my elbow. Doesn't anybody RTFA anymore?

      FTFA: So, what would you do with a space elevator connected to the Moon? "Plenty," says Pearson, "there are all kinds of resources on the Moon which would be much easier to gather there and bring into orbit rather than launching them from the Earth. Lunar regolith (moon dirt) could be used as shielding for space stations; metals and other minerals could be mined from the surface and used for construction in space; and if ice is discovered at the Moon's south pole, you could supply water, oxygen and even fuel to spacecraft."

      If water ice does turn up at the Moon's south pole, you could run a second cable there, and then connect it at the end to the first cable. This would allow a southern Moon base to deliver material into high-Earth orbit without having to travel along the ground to the base of the first elevator.

    • Re:Except.... (Score:4, Interesting)

      by AndroidCat ( 229562 ) on Saturday November 20, 2004 @12:03PM (#10875042) Homepage
      It would like when they were building the first highways across America. The company would build a "seedling mile" [stuhrmuseum.org] of good highway along a stretch of crummy road near some town. After people tried that mile of good road in the middle of a stretch of washboard, it was a lot easier to get them to vote for the taxes to pave more of it.
    • Actually their point was to be able to use the materials from the moon to build things in earth orbit without the big cost of boosting them all from the Earth's surface. Sure you would still have to bring things up from Earth but if you could cut the amount with lunar materials by say 50-75% that would be a very health savings.

      The space elevator is a wonderful idea, but I'd rather them give it a go on the moon first where it would cost us 10's of billions and be attached to a larger lunar mission instead

    • RTFA (Score:2)

      by p3d0 ( 42270 )
      The article discusses why this elevator would be useful.
  • So you'd also need to built a transport route between the northerly moon base and the equatorial lunar elevator. I suppose that would be a lot less effort than building a bloody lunar elevator though, given that we haven't even been to the place in around 30 years.

    There's a good reason to build a terran elevator. For a start, we live on this damn planet! I think that the logistical problems of building an elevator on the moon will outweigh the material problems of building one on earth.

    Of course, it could
    • So you'd also need to built a transport route between the northerly moon base and the equatorial lunar elevator. I suppose that would be a lot less effort than building a bloody lunar elevator though, given that we haven't even been to the place in around 30 years.
      Northerly moon base? The best-argued location I ever saw was for the lunar south pole; permanent sunlight, water, and constant ambient temperatures of -20degC.

      But, yes, a lunar space elevator would have to have an equatorial ground station, and

    • Re:Moonbase would be in the always-lit north (Score:5, Informative)

      by danila ( 69889 ) on Saturday November 20, 2004 @10:38AM (#10874626) Homepage
      RTFA. The logistical problems consist of launching 7 tons of kevlar cable to the L1 point 250 000 km from Earth. I am not saying there are no technological obstacles to overcome, but compared with Cassini probe or Mars rovers this is a piece of cake. There are existing rockets with that launch capacity, it doesn't take long to get there, it's cheap, easy and we get to test the space elevator prototype. There is simply no reason not to do it in the next few years.
    • I think that the logistical problems of building an elevator on the moon will outweigh the material problems of building one on earth.

      I find that hard to believe, considering that the materials needed to build a terran elevator don't even exist yet.

  • Mistake (Score:3, Insightful)

    by sconeu ( 64226 ) on Saturday November 20, 2004 @08:15AM (#10874091) Homepage Journal
    Unless we have a working lunar colony/base, it's useless.

    The whole point of the elevator was to make it easy to get out of Earth's gravity well. To get to a lunar elevator, you still have to do that.
    • Right. This kind of thing doesn't help build a lunar colony, since all of the problems in doing that involve getting things to the moon, not from it. Once we have a viable colony, maybe it could begin exporting, assuming it has anything to export (does the moon have any valuable raw materials? Is lunar rock cheaper for radiation shields than asteroid material?). However, the very things that make it easy to build a space elevator on the moon make the entire thing pointless. A relatively small magnetic
      • But wouldn't that require some form of energy, just to 'jump' into acceleration? This energy, whatever it may be, would also need to be refuelled (i hope no spelling error :)). And doesn't it require much more energy to rid itself of the moon's gravity?
    • Okay, so lets say that we now have a working
      space elevator technology. What possible
      reason could there be for such an elevator
      on the moon (at 1/6th Earth gravity)?

      The whole idea behind such technology is to
      cheaply lift material into orbit. The only
      thing the moon has (right now) is moon dust,
      and once those first samples came back at
      tremendous cost, what's the point? Just how
      much moon dust would be necessary to satisfy
      the demand on Earth? Even marketing the stuff
      on eBay has got to have some limit to dema

  • First things first... (Score:5, Insightful)

    by bani ( 467531 ) on Saturday November 20, 2004 @08:19AM (#10874100)
    ...how about long term stays on the lunar surface? As in months or years.

    How about a lunar colony instead of a freaking space station?

    Would seem to be a prerequisite for anything approaching a lunar space elevator.

    And long term lunar stays would provide valuable practice for something like a martian colony.
    • And what if a lunar space elevator is simultaneously a prerequisite for long term stays, colonies, mining, etc.? You have to do one of them first, why not the elevator?
    • Possibly because humans would be better able to endure a long term stay in a spinning space station with earth-like "gravity" than a long term stay in the moon's low gravity?
    • True. But a colony requires much more resources than the moon could provide, even if they did find ice, i think. With the elevator, one could retrieve small amounts of resources from the moon and put them into earth's orbit. As the article mentions, this is a technology which is well within reach. A colony however would require so many more things. And let's face it. What did we do with the moon once we were there? Collect a few samples and left? Why not try to use this elevator and try to maximize the poss
  • The mass of material required for such an elevator (while smaller than an Earth-centric one) must be pretty large compared to the mass that 1 rocket could launch to the Lagrange point.

    I'm glad I haven't heard many fearful and wildly speculative comments about space elevators. The most obvious one would be 'what if the cable breaks?'. Any Chicken Littles in our society would assume that lengths of the cable will fall, crushing sections of cities.

    A lunar elevator would show that such fears are unfounded.

    It
  • Sounds like one of those ideas that are theoretically possible but utterly impractical to implement.

    Yes the elevator could be built. What exactly are we so desperate for we can only get from the moon? Oh thats right, nothing, at least nothing that makes the expense of this endeavour currently worthwhile. The cable may be inexpensive but who wants to pay to put the lunar base in place and get the heavy mining equipment up there, cos that aint gonna be cheap. Also it conveniently fails to explain how we a
  • This has to be a vastly better alternative to sitting on our backsides contemplating our navels (or starting wars etc).

    Of course, the chance of any nation getting stuck-in is remote due to plain beurocracy. (We're back to contemplating navels)

  • For a second I thought .... (Score:3, Interesting)

    by Gopal.V ( 532678 ) on Saturday November 20, 2004 @08:25AM (#10874121) Homepage Journal
    I thought we were going to use the moon to anchor this to , instead of the typical big bulky sattellite.

    Relocating to the Moon won't help the project a bit if the raw materials (whatever) has to be brought from Earth . A mining/harvesting camp on Moon would be at least a few decades away, until then this can wait on the backburner. An orbital platform harvesting asteroids for heavy metals would rock ! (literally) . Would be nearer to earth and it would put solar sails in the domain of practical rather than as Sci Fi book fodder.

    Hmm... all the differential equations in Rocket Science confuse the hell out of me . I suppose the space elevator doesn't have the rocket's exponentially growing weight problem ?. (Now I know why they say "It ain't rocket science)

    I'd rather vote on the space catapult to launch rockets at Mach 3 (or higher) with something (jet aeroplanes or Maglev rails on mountains) . If the initial acceleration can be supplied by ground based non-moving power equipment, the rocket could go a looong way in reducing weight.

    Sadly the word space Catapult brings into mind unnecessary images of North Elbonia and .....
    • I suppose the space elevator doesn't have the rocket's exponentially growing weight problem ?

      The elevator has a similar problem, but I don't recall if it's exponential or geometric. (Despite common confusion there is a difference.) Each given segment of the elevator must support the segment below itself, plus itself. Thus, as you go "up" the elevator (which IIRC actually means "towards the middle" in this case), the elevator has to get thicker and thicker... at least if "normal" materials are used.

      That's
  • How about an elevator from Earth to the Moon?

  • The point of building on the moon (Score:5, Insightful)

    by Legion303 ( 97901 ) on Saturday November 20, 2004 @08:53AM (#10874202) Homepage
    Tons of people are complaining that this is a useless gesture, as the ultimate point is to transfer material out of earth's gravity well. But they're missing the point of building on the moon first. Think of it as a proof-of-concept. Once we have a working elevator in place, we can then test its performance and learn a great deal about how to eventually build one on earth.

  • Space Solar Power Satellites (Score:5, Insightful)

    by Baldrson ( 78598 ) on Saturday November 20, 2004 @08:56AM (#10874218) Homepage Journal
    Given the geopolitical pressure cooker over energy resources [telegraph.co.uk] there is a lot to be said for Gerard K. O'Neill's proposal [ssi.org] to use lunar materials to fabricate space solar power satellites [space.com]. The Lagrange-point elevator could replace the mass driver [ssi.org] in O'Neill's system and since the mass driver was the most problematic aspect of the proposal it may turn out that O'Neill's proposal just became a lot less risky.

    An effect of O'Neill's proposal is the creation of space settlements [aol.com] which could house thousands of times the land area of the Earth from asteroidal materials alone. The creator of the space-settlement FAQ [aol.com], Mike Combs, says in that FAQ to the question "Is space settlement a solution to the overpopulation problem?": [aol.com]

    Probably not. No space transportation system we can imagine (although that might be a significant qualifier) could keep up with the number of babies being born.
    This is ironic since O'Neill himself described just such a transportation system and projected depopulation of Earth to require an infrastructure not much larger than that supporting the commercial airlines.
  • ...the top of the elevator has to be in geostationary orbit, because the entire elevator is attached to the ground. The moon rotates once every thirty days. You can calculate, using this equation:

    orbital_radius^3 = (3,600^2 * surface_gravity * surface_radius^2 * orbital_period^2) / 2*pi^2

    ...the height of the elevator, therefore; for the moon it's 190000km. In other words, five times higher than one on Earth! That's nearly half-way to Earth; the gravitational disturbances from Earth's much greater mass c

    • You know, if this were anywhere but Slashdot I'd suggest that you could try to RTFA if you wonder about a claim in it.

      Then you'd find that the proposal is to put this at the L1 point. The Earth's gravity helps to hold it up, it's not entirely held up by centrifugal force.

    • Re:Sure, you could, but... (Score:5, Informative)

      by ZorbaTHut ( 126196 ) on Saturday November 20, 2004 @09:19AM (#10874294) Homepage
      "A lunar space elevator would work differently than one based on Earth. Unlike our own planet, which rotates every 24 hours, the Moon only turns on its axis once every 29 days; the same amount of time it takes to complete one orbit around the Earth. This is why we can only ever see one side of the Moon. The concept of geostationary orbit doesn't really make sense around the Moon.

      There are, however, five places in the Earth-Moon system where you could put an object of low mass - like a satellite... or a space elevator counterweight - and have them remain stable with very little energy: the Earth-Moon Lagrange points. The L1 point, a spot approximately 58,000 km above the surface of the Moon, will work perfectly."

      In other words, RTFA.

    • Re:Sure, you could, but... (Score:5, Insightful)

      by barawn ( 25691 ) on Saturday November 20, 2004 @10:13AM (#10874519) Homepage
      The moon rotates once every thirty days.

      It also orbits the Earth once every thirty days - in other words, it's locked in a 1:1 resonance with the Earth. This is of great benefit in this case!

      A little background:

      Space elevators need to remain stationary with respect to the body that they'll be attached to. With the Earth, that means you need to be rotating at the same speed as the Earth - in other words, GEO.

      With the Moon, however, you can either be rotating as fast as the Moon, or orbiting as fast as the moon, because the moon rotates at the same angular speed as it orbits! And there are 5 places where that occurs - the Lagrange points [wikipedia.org].

      From any one of those points, the Earth and the Moon are stationary in the sky - that is, you don't see either of them moving with respect to each other. Since the Moon's rotation is defined by its orientation with respect to the Earth, therefore, you don't see the Moon rotating. That is, you're in something that's exactly the same as GEO.

      Of the 5 Lagrange points, obviously L3 is silly - it's on the opposite side of the Earth as the Moon. So that won't work.

      L2 is similarly silly - it's on the opposite side of the Moon as the Earth. Could be useful for sending things to interstellar space, but not for Earth-Moon transits.

      So you're left with L1, L4, and L5. Obviously if you're talking about getting things from the Earth to the Moon, you'd want the one that's deepest into Earth's gravity well - and that's L1, "gravitationally halfway" between the Earth and the Moon. And that's what's being proposed.

      One helpful thing is that L1 is unstable - orbits tend to drift away from there. However, an elevator tethered to the moon at least anchors one of the unstable directions (radially towards the moon/away from the moon), and I'm not sure if the perpendicular direction is unstable as well. So it may be that an elevator in that position is stable, and that unpowered objects will tend to move away from the elevator. You'd have a natural deflection mechanism. Pretty interesting!

      Actually, a combination of an L1 and an L2 elevator could be quite interesting, though you'd have to build something like a railway around the Moon. Once you do that, though, you could go out past the L2 point, and you could sling yourself into interplanetary space. I'd have to work out how much of a boost you could get, but Mars orbit seems quite reasonable.

      It's not as good as a terrestrial elevator (because the Earth rotates so quickly, so you can steal more of the Earth's angular momentum), but it's certainly currently feasible.
      • and I'm not sure if the perpendicular direction is unstable as well.

        Sigh, I could've tried reading the All Knowing Wikipedia : L1 is stable in the perpendicular direction, so an L1 elevator would be completely stable. Interesting!
      • L1 is unstable... I'm not sure if the perpendicular direction is unstable as well

        The instability is only directly along the earth-moon axis. Imagine a triangle based on the earth, moon, and the object. The earth-moon axis is the base of the triangle, and the other two sides of the triangle represent the earth's and moon's gravitational pulls. The two sides of the triangles nearly balance except that they both pull in the same direction back towards the axis.

        So a counter weight on the earth side of the po
  • Anyone else noticed the McDonalds wrappers and crap we leave every day on Earth? Do we really want that on the Moon?

    The human race as a whole is not ready for population of any planet which can't naturally support us. If only takes some bully to smash another kids space suit or some idiotic kids to think it's fun to throw bricks at a glass dome and we have a major emergency.

    This isn't sci fi here, the stupidity involved in the human race would destroy anything we set up.

  • Geosynchronous orbit? (Score:2, Insightful)

    by mowler2 ( 301294 )
    The masscentrum of the elevator must lie in the geosynchronous orbit. Does the moon have a geosynchronous orbit around itself (due to the slow rotation, 1 rotation in 20-something days)?

    I guess earth lies in its geosynchronous orbit, since we always see the same side of the moon, but an elevator from earth to the moon would be a little bit long, eh? :) (likewise if the elevator is placed on the other end of the moon). Seemes like it is best to start with earth after all?

  • Did Anybody RTFA?! (Score:4, Insightful)

    by TFGeditor ( 737839 ) on Saturday November 20, 2004 @09:26AM (#10874317) Homepage
    The comments on this topic make it clear few, if any, RTFA. 90 percent of the comments should be modded "Redundant" since the article answers the very questions posed.

    Geekdom sure ain't what it used to be.
  • In "the Moon is a harsh mistress" (heinlein), they used a great big railgun to accellerate boulders enough to get them into orbit. course, this was later used during the revolution as a threat weapon to declare independance from the earth.

    • Terrorist! (Score:4, Interesting)

      by mangu ( 126918 ) on Saturday November 20, 2004 @10:28AM (#10874584)
      I guess "The Moon is a Harsh Mistress" will be one of the first books to be banished and burned once the revised PATRIOT act goes into effect ;p


      But you are absolutely right. Having no atmosphere, the Moon is the ideal place to put a railgun. Besides Heinlein, many other authors have used that concept, among them Gerard K. O'Neill, who popularized the L5 orbit concept.

  • Geez you guys (Score:5, Insightful)

    by Rhinobird ( 151521 ) on Saturday November 20, 2004 @09:31AM (#10874340) Homepage
    To everyone that says a lunar elevator would be useless right now, did you read the article? He says we can make this thing right now. With current materials, and launch cababilities. All that it needs is money and people to build the flipping thing and it can be done. Now.

    And just because it's on the moon and not earth, doesn't mean it can't be quite useful. Imagine being able to send lunar rovers with return capabilities without having to give them heavy expensive fuel for the return trip. Just hop on the elevator and from L1, just a small thruster push and back it comes.
  • Seems to me that the only way to do this cost-effective is to first build a space elevator on earth in order to get the material needed to the moon cheaply...

    Funny, really.
  • Also good for delivering stuff into the Moon's gravity well... which is something you'll want to be doing from time to time. Delivery vehicle stays well out in space, doesn't have to waste energy getting down and getting up again.
    More efficient than parachutes.

  • Doesn't anyone read the actual article? (Score:5, Informative)

    by Fraser Cain ( 203191 ) on Saturday November 20, 2004 @10:48AM (#10874666) Homepage
    I wrote the article, and now I'm reading through the Slashdot comments, and they're killing me. Didn't anyone actually RTFA?!?

    Let me clear these up...

    1. The cable would be 58,000 km long. This is the distance from the Moon to the L1 point, which is the balance point of gravity between the Earth and Moon. The Earth pulls the elevator straight using its gravity. If you looked at the Moon from the Earth, the space elevator would always be at exactly the same place on the Moon, always pointed directly at us, like we're tugging at it with the Earth's gravity. This has nothing to do with centrifigal force, like an Earth-based elevator where the counterweight keeps the cable taut.

    2. Because of low gravity on the Moon, you could build the elevator with commercially available materials on the market today, like Kevlar or M5. The cable would be light enough that it could be launched on a single heavy lift rocket available from Arianespace, Boeing or Lockheed Martin.

    One launch = one lunar space elevator

    3. You could connect a second cable to the Moon's south pole, so the two cables form a V, and then bring up water ice from the south pole. This would put water, air and rocket fuel into high Earth orbit at a fraction of the price of bringing it up from Earth.

    4. As you make the cable longer, it allows you to kick objects into high-Earth orbit. You could transfer materials from the Moon into orbit for relatively little fuel.

    • I am not a physicist or rocket scientist, but a few questions pop out:

      The cable would be 58,000 km long. This is the distance from the Moon to the L1 point, which is the balance point of gravity between the Earth and Moon.

      Wouldn't the cables center of mass need to be at L1 or slightly above (relative to the Moon), rather than the end of the cable? If one end of the cable were at L1 and the other end on the moon, the moon's gravity would have a greater effect than the Earth's gravity, so the cable woul

    • Re:Doesn't anyone read the actual article? (Score:5, Insightful)

      by Jetson ( 176002 ) on Saturday November 20, 2004 @01:23PM (#10875520) Homepage
      The cable would be 58,000 km long. This is the distance from the Moon to the L1 point, which is the balance point of gravity between the Earth and Moon.

      The cable would have to be much longer than that. As the cable is extended toward the surface of the moon, a counter-weight would have to be extended toward the earth so that the elevator's center of gravity would stay at L1 (or else the whole structure would fall to the moon's surface). Once the elevator reached the curface of the moon, the counter-weight would have to be extended yet further in order to offset the weight of the objects traversing the cable. The total length would have to be more than 120,000km.

      The concept also doesn't mention coriolis force. The shortest cable would be one that anchors to the lunar surface direcly below L1, however objects travelling on the cable will impart a force onto the cable at 90 degrees to their direction of travel. The base would therefore be best located east or west of the ideal point depending on whether the net traffic on the cable is upward or downward.

      • Re:Doesn't anyone read the actual article? (Score:5, Insightful)

        by trixillion ( 66374 ) on Saturday November 20, 2004 @06:11PM (#10877151)
        Actually you would want the center of mass to extend just past the L1 point. Assuming the tether is secured to the Moon, then the tether will hold taught because the saddle equilibria about L1 will always being pulling towards the Earth. Surprisingly, this extra tension is all that is necessary to make L1 a point of stable equilibria because the other two dimensions were stable to begin with. I had done very similar research a few years ago on my own and was unaware of Pearson's work, but came to the same conclusions. The Corialis force has to be taken into consideration but so long as this force is kept below certain limits then it has no effect on the overall stability of the system.
    • This has nothing to do with centrifigal force, like an Earth-based elevator where the counterweight keeps the cable taut.

      Sigh. This has everything to do with centrifugal force. It is exactly the same as a terrestrial space elevator. That's why you could build a cable to L4, or L5, even though gravity doesn't appear to balance there at all. It's all about solving the 3 body problem in a rotating frame.

      When we talk about a space elevator for Earth, we're talking about building a cable to geosynchronous orb
  • I hope some kind of alien doesn't mistake our two planets connected with a cable to eachother, for a giant bola.
  • Hmm. A horrible idea popped into my head. Somehow this scheme looks like a grand plan to deorbit the moon (grinning). Well, it *is* a satellite, and that *is* a tether, and there *is* a magnetic field.

    For sure, it's the solar rather than the earth's field that bothers me, but since the earth-moon system is orbitting the sun I'd expect some kind of generator effect. Not to mention the fact that nobody really has a clue about the dynamics of the solar field.

    So, even after somebody does some calculations to
  • (Yes, some of you already get this.)

    The elevator does not go from the earth to the moon.

    The moon is not in geostationary orbit around anything. It rotates to keep the same side towards us.

    The top of the elevator would be at Lagrange point L1, which is the point at which Lunar gravity and Earth's Gravity are balanced. It is balanced, but unstable. Stationkeeping would be necessary.

    People would rarely use the Lunar Space Elevator for personal transport. It would be only for cargo. (Similar to the long awai

  • The L-Prize (Score:3, Insightful)

    by Baldrson ( 78598 ) on Saturday November 20, 2004 @11:19AM (#10874801) Homepage Journal
    This would make a great prize:

    $100M for the first kg of lunar material moved, without rocket propulsion, to a Lagrange point.

  • Personally I'm a little iffy about altering the mass of a giant object that orbits the Earth. I don't know about the physics here but how would it affect the orbit of the moon if we started increasing its mass by bringing materials from earth up there?
  • Sometimes someone mentions an idea and a million people kick themselves for not seeing it's logic and beauty earlier. Great idea!

  • On improving reading ability, analytical and logical thinking amongst the general population?

    Looks like a more urgent issue. :)

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