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Space Science

Going Up? 132

Posted by michael from the if-only-we-had-the-vision dept.
An AC points us to this article about the space elevator concept, once solely the realm of science fiction but now coming a bit closer to reality. The main problem seems to be the lack of some material with the ludicrous tensile strength required. Oh, and an asteroid to anchor it. And the willpower to actually build it. Check out the slashdot discussion of an earlier spacescience.com article on this idea as well.
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Going Up? More

Going Up?

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  • Re:What's the american degree for -1? (Score:1)

    by Anonymous Coward
    The purpose of this elevator is not to go up magcially by itself.


    Although in reality it would seem pretty magical. Realize the following: anything on the bottom half of the cable would be pulled "down" to the earth, and anything on the top half would be pulled "out". Which means that whichever way you travel, halfway you'll be expending energy move, and the other half you can be _storing_ energy as you brake.

    The result: if you send the "elevator car" up in a rocket and latch it onto the middle first, the only power you'll ever need for this thing is to compensate for friction, engine inefficiency, and differences between mass lifted and mass lowered. Which, while still a lot, is still a hell of a lot less than doing it the hard way..

    The other neat thing: you can put a massive space station on the middle and/or end of the tether for relatively cheap, since lugging the materials over is almost free compared to the prices of lifting it by rocket. I've heard dreams of orbital refueling stations (for trips further out), orbital resorts, whole cities up there...Plus: parts are less expensive because a) they can be quickly and cheaply replaced and b) they can be cheaper to make because its easy to use redundant units that are, individually, less foolproof than the ones used in current space endeavors.



    The caveat: first we have to figure out how to build the damn tether, then we have to actually do it and test it, then someone's gotta pay to set it up, then someone's go to actually go DO it.

    Smaller versions wouldn't be AS cool, but they'd still be a godsend for all things space-related.

  • Re:Silly question about vacuums (Score:2)

    by Anonymous Coward
    Not a silly question. :)

    I used to think about this when I was a kid, not knowing too much about how the atmosphere stayed where it was.

    Nah, a big tube into space wouldn't leak out our atmosphere simply cause gravity keeps it in place.


    Zero Kelvin
    neux.org

  • Been There... (Score:2)

    by Anonymous Coward
    ...done that [amazon.com].

    Thank you.

    -- Patrick Bateman, Esq.
  • AFAIK, the cable is to be deployed from a satellite in GEO. That means, one half (sub-GEO) hangs towards earth (gravitational), the other half "hangs" away from earth (centrifugal).

    Ergo, the cable is under tension all the time and has no chance to develop a knot.

    Regards, Ulli

  • All the greatest failing of the whole Space elevator concept stem from the idea that this elevator goes all the way up in a single step.

    How about the 1st step going to a platform supported by a cluster of blimps that will drift a little with the wind, but only as much as the fans let it. This platform will nead refueling by conventional means. No bigy.

    Above that you have another platform in the stratusphare kept stable by jets.

    And so on ontil you get out to the last haul into orbit.

    breaking it up this way achives several things.

    #1 if it falls it will just be a part of it. Dangerus but a lot less so.

    #2 It should be more stable.

    #3 It brings it somewhere within sanity. I.e. We could build some of these stages already.

    #4 when there is a failure somewhere on the elevator there is usualy a stop so not everyone will be left dangling on the wire. Only a few :). Those will usualy have a way out. I.e. Back down to the last platform.

    This 31 mile tower is ridiculus. For now. A few baloons hovering at 31 miles up is not however. Ask your local metrologist.

    PS: Be carefull with how the baloons are constructed. We don't want them floating to high, deflating, faling or exploding.

  • Huh? (Score:2)

    by roystgnr ( 4015 )
    I don't know where to begin with this one.

    First of all, Storrs-Hall just described a "mass driver", but one propped up on a 100km high tower for God knows what reason. Which proves:

    He doesn't know anything about orbital mechanics, but just thinks you need to "point up to get into space". Well, that's probably unfair; he at least got orbital velocity about right.

    He certainly doesn't know anything about mechanical engineering, or he'd realize that making a 100km structure that will support tension may be possible, but making one that won't buckle under compression is ridiculous. Buckytubes may have a hundred times the tensile strength of steel, but they still bend real easy...

  • Honestly, now, has Slashdot become infested by morons? Look at all the crap that's been moderated up on this article! There's the "won't it suck away all our air" question, the "will it change our orbit" question, and the mumblings about shear stress...

    Don't take this the wrong way: those are all valid questions to ask, I don't think they should be moderated down, I hope they all get accurate responses, and I hope the responses get moderated up. Ignorance is correctable, and the right way to correct it is by asking serious questions.

    But could you imagine this kind of thing happening in a computer science story? Would someone who asked "Won't Lunix let the hackers steal my computer cause it's open source?" get stamped with +1, insightful?

    Ok, done ranting now. On to your question.

    Serious question: Wouldn't such a thing affect the earth orbit?

    Quick answer: Yes, but not so you'd notice.

    Building the beanstalk, if it were done with asteroidal materials, would add mass, angular momentum, and an increased moment of inertia to the Earth. Depending on how the asteroid was captured, this could raise the earth's orbit slightly, but would leave the rotational period (length of a day) unchanged. Launching interplanetary vehicles from the beanstalk would remove angular momentum (and a little mass) from the system, slowing the rate of a day slightly.

    If the beanstalk was built with terrestrial materials (building one thread first and hauling the rest up on that), it would increase the moment of inertia of the planet-beanstalk system slightly, without adding any angular momentum. Again, the day would be slowed slightly.

    But, the key word here is "slightly". By slightly I don't mean days that are one second longer, I mean days that are (1 + ~10*(mass of beanstalk / mass of earth), which works out to something like 100 picoseconds, longer. Use the beanstalk to launch continual interplanetary payloads for a few millenia, and maybe we'll slow the rotation of the earth down by a microsecond. This is all back-of-the-napkin arithmetic, of course, but if my conclusions are too optimistic by a factor of a thousand I'm still not nervous.
  • the only point in the tower where you can drop off and be in orbit with a little push is at GEO.

    Almost correct; the only point where you can drop off into a circular orbit is at GEO; there's a huge range of hyperbolic orbits you can get into (well, hyperbolic w.r.t. the Earth; enough to take you to the inner planets at least) by dropping off the tower above GEO, and a range of elliptical orbits (including one with perigee in the upper atmosphere, making aerobraking into equatorial LEO a cheap possiblity) you can get to by dropping off the tower below GEO.

    Throw in some high efficiency rockets (ion engines, plasma rockets - all the sorts of things you can't use on a launch vehicle because they're too low thrust), and you could get into any Earth orbit with a lot more payload, a lot cheaper than with a conventional rocket.

    Or perhaps I should say marginally cheaper; as the amortization of the original construction cost should be considered. Of course, building this thing means manufacturing thousands of tons of buckytubes, each thousands of kilometers long. IIRC, current buckytube manufacturing is on the order of $2000 a gram, for micrometer-sized things that might be useful in electronics, MEMS, or nanotech, but certainly wouldn't be as a structural material. We've still got a little technology to research...
  • Do you realize how much energy our Sun is spitting out every second? And how little of that energy happens to impinge on this tiny planet for us to use?

    How about matter? I'll spare you the numbers, but it wouldn't take a very large asteroid to supply our entire civilization's structural metal requirements for centuries, and to provide enough mass of everything else to make the phrase "precious metal" an oxymoron.

    There's a nice Kuro5hin discussion [kuro5hin.org] going on right now about overpopulation, including the question of what is a "sustainable" population for humanity. The answer isn't encouraging; our fossil fuels won't be around in a few centuries, our fissionable metals will give us a few centuries more... and then what? Solar power? Not concentrated enough, unless you've got a plan to reduce our population 10-fold, or pull in extra power from space. Fusion? That's better (assuming we get it working eventually), but then you run into the problem that the cleanest fusion fuel, He3, only exists in quantity on the Moon and outer planets. Even if you don't see the value of going into space to support life there, eventually we'll want to leave this planet to better support life here.

    The solar system has the resources to support quintillions of people; unfortunately for us an insignificant fraction of those resources happen to be on Earth.

    An elevator to nowhere. Imagine how silly it'd look.

    So anyway, like I said, you've got it exactly backwards. It would be an elevator to everywhere.
  • Oh dear. How about that public hair, huh? Nothing like screwing a punchline.

  • You bring up a good point. Not only is tensile stress important, but the "cable" would be under very high shear.
  • People I'm quite admired abotthis discussion. I have seen LOTS of vapourware stuff in /. I have seen people calling for panic while on Y2K.

    But your COLLOSSAL lack of physics is, for me, extraordinary. It's just fantastic to see how people go by things like "bringing pieces of Space to Earth", "elevators". How you can forget that Gravity decays at the square of the distance? Do you know what is angular momentum? And how can you dare to think about something pushing this elevator up in vacuum, by itself. Hey, as anyone forget Newton's Third Law? Sorry to be so flamously bitter, but do they still teach it on school?
    And what about friction? The stuff is there and no one will kick it out...

    And some people come here moderate my comments to 1 while pushing other weird fantasies up? People give me a break. If anyone of these will call himself a Space Geek, then please get to the open and look at that damn Space. Look at it and then look at your own feet. Saw them? You are bound to this piece of dirt. And this damn piece of dirt will be you damn home and grave because you don't know a thing about the world you live in. Like 1000 years ago, you are still a serv of your own ignorance. And you are cursed to be so because you wish more for your feet than for yourself...
  • If it was a ring you could spin it at any speed you wanted because it would never "fall" to Earth. It would be "balanced".

    And with regard to the vacuum question, what do you think stops our atmosphere from disappearing into the vacuum of space at the moment? Why, gravity of course (and a little protection from the solar wind courtesy of our magnetic field).

  • So let's see.

    We lack the materials science to build it, the transportation science to obtain the counter-weight, and the funds to make it all happen.

    We've got everything else, though. We're home-free.

    -
  • Storrs-Hall just described a "mass driver", but one propped up on a 100km high tower for God knows what reason.

    The reason is that, at that altitude, you're out of the atmosphere so you don't have to deal with air resistance.

    He doesn't know anything about orbital mechanics, but just thinks you need to "point up to get into space".

    You are critiquing some other proposal with which I am unfamiliar. I have heard of variations where the linear induction motor runs up the side of a mountain (perhaps this is where you got the "point up" idea) over vastly shorter distances, and clearly this is quite stupid. But obviously you didn't follow the link and you haven't read the proposal under discussion here. The platform's upper surface is horizontal; over 300 km it picks up some curvature. It is consistent with a circular low-earth orbit. Perhaps you've heard of these. They are used extensively by satellites.

  • John Storrs-Hall's space ramp [imm.org] is another interesting approach to cost-effective space launches. Again, it depends on materials that are a little better than what we have today, but not too much better. The recent materials work on buckytubes may make the space ramp feasible.

    The space ramp is about 100 km high and 300 km long, with a linear induction motor running its length. You take an elevator up to one end, hop on the induction motor, and get accelerated at 10 G for about 80 seconds. This puts you in low-earth orbit, at an amortized cost of 42 cents per kg. Prior to amortization, you'd be paying about a buck a kilogram. The cost for space shuttle launches is about $10K per kilogram.

  • Dunno what these other people are babbling about. The original space elevator that AC Clarke came up with was in The Fountains of Paradise.
  • Uh, so what exactly is considered "launch cost" with space elevators? Is it merely the price of getting a payload delivered to orbit once the thing is built (theoretically)? Well in that case I can launch comsat sized payloads for about 75$ using a linear accelerator, oh yeah, once one is built and we have some vehicles to use on it and whatnot. Space elevators are nice prospects for societies living a hundred years from now that need to make regular orbital runs to space stations and lunar cities. In 10 to 20 years we may have the ability to make labrotory quantities of the requires materials to make a space elevator but don't think a bellhop is going to be announcing "stopping on the third, fourth, fifth, floors and low Earth orbit". In 20 years unmanned orbital delivery vehicles will be the norm and any manned flights will be made by more specialized vehicles. Why the specialization? If you have a low overhead vehicle that just transports people and consumables to and from the space station(s), you're saving money on excess vehicle you're not also sending up to the station. Rather than the space shuttle imagine something more near the size of a Lear jet transporting crews and consumables to and from the space station(s). A similar system could be used to cheapen satillite launches, only using a vehicle designed soley for unmanned payload delivery. I think one of the biggest reasons for this is adapability, right now there are not even a handful of facilities that are capable of launching the space shuttles. If the scope of the vehicles was reduced you can also eliminate some complexity in terms of support. Any desirable plot of land, maybe locations with higher elevations than Cape Kennedy say...Colorado, could be used to launch a smaller space vehicle. Johnson space center is still going to manage the launch, if you're got addequate support facilities at the launch site you don't need a whole lot else. This is a MUCH more reasonable expectation in 20 years than space elevators. It isn't like I don't like the idea, the concept is more of a pipe dream than anything else right now and probably will continue to be for a good stretch of time yet.
  • My understanding of this concept is as follows: You take a strand of material, and, starting from GEO, extend the strand in both directions until one end of the strand is touching the earth and the other end is sufficiently far enough into space that the centripedal force counteracts the force of gravity.

    As far as I can tell, this scenarion doesn't require latching on to an asteroid. Now, it may be that the tether needs to extend a million miles into space to counteract the gravity.
  • I don't know about you, but last time I checked space was a vacuum. If we put a platform in orbit that had an elevator going from earth to outside our gravity well wouldn't it serve as a tube to just suck our atmosphere out into space?

    Just a silly question.
  • Sure, make it tall enough for the top to be in a geosynchronous orbit.

    But wouldn't all the elevations below that be in faster orbits? Even if it had the tensile strength to survive, wouldn't it "stand" with one heck of a gimp in it?

    --
  • Perhaps I've misunderstood the proposed space elevator, or I've misunderstood your post, or perhaps you've read too many sci-fi books - but according to the article we're talking about a tether 15 kilometers long. The diameter of the earth at the equator is roughly 42000 kilometers. You would need 2800 cables that length, laid neatly end to end, just to get around the earth *once*. I don't see how it could "wrap around the entire Earth".

  • OK I didn't read the article fully. 15 kilometers is a proposed experiment. So how long would something like this need to be? The atmosphere isn't too much thicker than 15 km anyway ..

  • It does seem like experiments with tethers show they are balky and hard to work with. It may just be a matter of learning the right materials and techniques, but I expect that there will be a lot of failures before there is anything like reliable success. This may be part of the learning process, but I expect it is unlikely that public support for such a project would continue beyond the first couple of disasters -- the public has little appetite for failure, as necessary as it may be on the road to success.

    By the way, my wife's an oceanographer, and they sometimes deploy experiments on cables that can develop knots which occupy a volume larger than the ship deploying them (the technical term for such as knot is a "wuzzle"). Unless you could keep the series of long lines you would need to hoist the final tether taught and unbroken, you could end up with a knot the size of a large city. If the line were made of an ultra-durable material you could have a very interesting situation on your hands.

  • The centre of mass of the earth will change a tiny little bit; quite some mass is moved rather far away from the centre. Therefore the rotation axis of the earth will shift a little bit and the orbit around the Sun might shift a little bit.

    Dislaimer: This may be bollux. But maybe not.

  • Good idea. That makes me think: the endpoint of the cable has to be in an orbit so high that the cable will not fall if an elevator would `pull' it down. That would mean there's a rather strong force pulling the cable away from earth (since the elevator would otherwise pull the cable back to earth). I wonder how one would connect this to the earth. Do you also have nice idea's about this?
  • I understand the space-mount-point will be some sort of sattelite OUTSIDE a geocentric orbit; it will be held on it's place by the elevator-cable itself; without the cable it would fly away into space. The centrifugal force has to be larger than the sum of earth's gravity and the force of the elevator pulling itself up along the cable.

    This will cause the cable to be under tremendous stress; the satellite pulls it into space while the earth pulls it back. I'm not an expert, but I conclude from this that in the middle of the cable the stress on the cable will be more than twice earth's gravity pulling on half the cable....e.g. if the cable has to be 20000km long and it is 10 grams per meter, it would be 100000 kilograms weight hanging from the cable...and an equal force the other direction. That makes a force equal to the gravity on 200000 kilograms...nice:)

    Experts: please correct me if I'm wrong.

  • HerringFlavoredFowl wrote: "If you want some real action become a Nasa click worker at http://clickworkers.arc.nasa.gov/top
    Maybe Slashdot will even do a story on it...

    I wait with herring baited breath"

    You mean like this? :)

    http://slashdot.org/article.pl?sid=00/12/16/1844 23 8

    timothy

  • Ektanoor, I've seen quite a few of your posts here before, and usually I think you're pretty much on the mark--but here, I've got to say, you're quite wrong.

    Do the orbital mechanics. Is it possible to have a tether from past-geosynch orbit down to the Earth, with its center of mass at geosynch? -- Yes, it is. We are aware of no fundamental laws of the cosmos which forbid this. Is it easy to do this? -- Yes, it is, provided that your materials science is suitably advanced. Is our materials science that advanced? -- No, not yet.

    Friction really isn't all that much of a problem. Why? Because the most atmospheric friction you get is in the first 75km, and in the first 75km the tether is essentially at rest with respect to the Earth. You don't say "this vase that's sitting on my desk suffers friction losses," do you? No, because friction is associated with movement.

    Insofar as propulsion, in case you haven't noticed, we're living on a huge magnet. We're going to have a tether made of electrically-conductive carbon going up to geosynchronous orbit. I don't know about what they taught you in school, but at Cornell they taught me that if you move an electrically-conductive material through a magnetic field, an electric current is induced in the material.

    This means that there are megawatts of power available for the taking, entirely as a fringe benefit of having the tether. That electricity can then be used to propel the elevator up the tether.

    In short, Ek, I think you're really wrong here. Nothing in physics says this is impossible; in fact, physics says it's easy, given the right materials science.
  • An added bonus of the whole beanstalk idea is that as the structure passes through the earth magnetosphere you'll generate one hell of an induction current. Anyone for wads of clean energy? Of course, you'd probably need most of it to push vehicles up the 36,000 km.
  • actually, the iridium satellites would be on the first or second floor. they are in very low orbits compared to mir and the space station.

    i think mir might be on the groud floor soon anyway :)
  • No, than you would create an atmosphere on the moon! (And the atmosphere of the earth will be somewhat thinner). But I guess the created moon-atmosphere will eventually dissipate because of lack of gravity and high temperatures.
  • But are carbon nanotubes that strong? I thought they were having problems manufactureing them that strong...

    Not per se, the problem is that nanotubes don't stick to one another very well, and the longest ones are only around 100 microns long. You can get around the length if you can braid them together, but they don't stick together unless they're long enough...kind of a catch-22, at least until we learn how to make longer nanotubes.

  • If one is shot down (such as in war) or it falls for any other reason, the cable would wrap around the entire Earth and kill everyone within quite a few miles of the equator.

    Actually if it is "shot down," it will probably be cut by weapons launched from earth's surface or atmosphere, which limits the length of falling cable to a few dozen miles. The rest of the cable would actually move away from Earth.

  • It's (theoretically) much, much less expensive to launch from space than it is to launch from the planet's surface. It's possible that something like this could make the use of local space cost-effective.

    I've heard the numbers before, but I can't recall off the top of my head...

    I know for certain that current "shipping costs" to get into space are roughly US$10K/lb. The space elevator should reduce that to something like US$200/lb. if I remember correctly (it may be lower).

    Never forget the reliability factor. We think space shuttle flights are routine, but they're not very frequent, which means the low number of disasters is primarily due to the low number of flights. From what I've heard directly from NASA, if one shuttle were launched every day, we should expect to lose one every year, give or take a few months.

  • I think money is a lot better spent on the international space station or new energy sources to propel new spacecraft. I think any money spent on even planning it is a waste and may as well be put towards the above causes.

    I take pretty much the opposite position, since I've seen some of the numbers and caught a glimpse of how things are run. Unfortunately our governments don't like sharing information (cold war habits die hard, I guess) so frequently scientists from different countries are not allowed to collaborate on experiments. To me, if scientists from different nations can't work together, there is no real purpose in having an "international" space station.

    As for propulsion, what type do you mean? A space elevator would lower the cost of getting into geosynchronous orbit tremendously. From there, it's much cheaper to go anywhere else. Just about all of the new propulsion schemes I've heard of either don't produce enough thrust (ion propulsion) or too much radiation (nuclear) for the first part of the trip.

  • $2k-3k for an orbit ride up? It would be the hot vacation spot of the century.

    DB
  • Robert L. Forward also does a lot with tethers/elevators and other radical propulsion systems (including monopole magnets) in his books, too. I highly recommend his book Dragon's Egg, about contact between humans and aliens living on the surface of a neutron star(!)

    No amazon url due to patent madness. Choose any online source you want for more info...
    --
  • Actually, no. The parts that are 20,000 miles up have enough velocity to fall into an orbit that misses the Earth. I'd have to run some numbers to be able to tell you exactly how low you could be on a synchronous skyhook and avoid colliding with the planet if you cut yourself loose, and there remains the fact that parts of the skyhook quite a bit below that could remain in orbit if they just stayed attached to the parts that are higher up. Getting down from there might not be fun or safe, but you'd have better options than a rapid descent to a fiery end.

    "
    / \ ASCII ribbon against e-mail
    \ / in HTML and M$ proprietary formats.
    X
    / \
  • and marianas trench is like 6 or 7 deep.

    but I get your point, 31 miles is an awful tall building

  • Um...if the cable is straight, the whole thing will be in geosynchronous orbit..

    right?
  • Nuclear rockets. Too messy. The NERVA program made real progress, but open-cycle nuclear reactors spray radioactive waste. Closed-cycle ones are too heavy, and messy if they crash land. Orion, the A-bomb powered spacecraft, was even worse in that regard. Still, if you launched from, say, halfway between Cape Horn and Antartica, where South Africa once tested an A-bomb without bothering anybody, it might work.

    I don't think the idea was ever to launch them from the Earth's surface using nuclear engines. More like assemble them in orbit or on the moon and then fire them up.

  • Space Teathers and elevators (Score:3)

    by GryMor ( 88799 ) on Thursday December 28, 2000 @02:27AM (#1403903)
    I have attended several panels by Dr. Robert L. Forward on the subject of space teathers and elevators using current materials. Interested parties should check out his company, Tethers unlimited Inc [tethers.com] as well as his personal site [whidbey.com]. I don't know where he will next be lecturing, I last caught him at VikingCon 17 (Western Washington Universitie's SciFi convention).
  • Humans regularly do 10+ g's in centrifuges. Humans have done more than that on rocket sleds (given, all the capillaries in their face broke and they were as a result bruised all over).

    10 g's accelerating you while you face forward is not so bad as 10 g's in a jet even. The latter forces blood into your feet, causing you to pass out. The former would just force blood to the back of your body. If sitting, this would simply result in blood flowing out of your legs and into your chest and head. Big deal.

    On the other hand, at around 47g your eyes explode and you die.
  • The poster clearly referred to Robinson's Red Mars, wherein the elevator in question is separated from the asteroid. Please check your references before you post.

    Oh, and go read the book. It's well worth it, and not just for the large divot they take out of the equator.

    KdL

  • As I recall the electrical energy costs are around US$1/lb to GEO, and since the propulsion and guidance uses no physical contact with the elevator there is essentially no wear and tear. OTOH, there would be huge construction costs to write off, but it would still probably not cost more than, say US$10/lb assuming a large amount of traffic.

    /Dervak

  • Each equatorial base site that anchors space elevator operations would feature a huge tower that is a true skyscraper at 31 miles (50 kilometers) tall.

    A building that's 31 miles high??!? Isn't Everest about 2 miles high? And isn't the Mariana Trench about 5 miles deep? And they say we'll have a man-made building finished "50 years away probably" that will be 31 friggin' miles high?

    What kind of bud are these guys smoking?

    Trains stop at a train station. Buses stop at a bus station.

  • hmm I can't remember which Arthur Clarke book that is? enlighten me, i gotta read it again! :-)
  • I've always been a big fan of cold fusion powered teleportation devices myself.
  • Thats an Escalator to nowhere

  • I think money is a lot better spent on the international space station or new energy sources to propel new spacecraft.
    I think any money spent on even planning it is a waste and may as well be put towards the above causes.. (Untill we have the resources if we ever do)
    just my $AU 0.0375

  • For More Info (Score:3)

    by Cheshire Cat ( 105171 ) on Wednesday December 27, 2000 @11:54PM (#1403912) Homepage
    An interesting article, but a little light on the details. There is a really good piece on how space elevators work here. [howstuffworks.com]
  • The middle (center of mass) would be in geosynchronous orbit, not the top.

  • What if you get stuck (Score:3)

    by Travoltus ( 110240 ) on Wednesday December 27, 2000 @11:49PM (#1403914) Journal
    on the 150,000th floor?

    I doubt there's enough Mentos in the world to get ya out of that situation :)
    ========================
    63,000 bugs in the code, 63,000 bugs,
    ya get 1 whacked with a service pack,
  • > I don't know about you, but last time I checked
    > space was a vacuum. If we put a platform in
    > orbit that had an elevator going from earth to
    > outside our gravity well wouldn't it serve as a
    > tube to just suck our atmosphere out into space?

    That is exactly like saying that if I drop a drinking straw into a glass of water, the water in the glass will spontaneously shoot out the top of the straw and empty the glass. Clearly that would never happen with a straw that was 50 cm long, why would it suddenly happen if the straw were 32000km long?
  • Um, it's actually Clarke's idea, fleshed out hugely in Heinlein's "The Moon is a Harsh Mistress", and developed by actual trained engineers in the early seventies during the L5 era. I forget what Clarke called it, but Heinlein called it a catapult, and the Princeton group called it a mass-driver.

    It's a great idea. It works fine in test models. We could probably build it, especially with the recent developments in workable maglev. But without a nation that understands science, or space, or why it's important to go, it's not happening for decades. If ever.

    The U.S. will never build a space-based civilization. We're too fat and self-absorbed. We don't understand math, we hate science, and we distrust brainiacs. We'll spend the next 50-100 years debating theology's place in government, and refighting the civil war in endless ways.(if you don't think Bush's election was a victory for the New Confederacy, think again.)

    Less negaitively, I think that space may be eventually be colonized by smaller nations, who have less investment in history and more hope for change in the future. Look to them for interesting projects.

  • Each equatorial base site that anchors space elevator operations would feature a huge tower that is a true skyscraper at 31 miles (50 kilometers) tall.

    Think guyed tower, not building. The problem is dealing with wind loading for the part of the tower that's in the atmosphere.

  • Space travel isn't feasible (Score:3)

    by Animats ( 122034 ) on Thursday December 28, 2000 @09:04AM (#1403918) Homepage
    Why space travel doesn't work:
    • Chemical rockets. Chemical fuels aren't powerful enough for useful space travel. Even with the best possible fuels, you either need disposable stages or have tiny payloads for the size of the craft. Heinlein pointed this out in the 1940s.
    • Nuclear rockets. Too messy. The NERVA program made real progress, but open-cycle nuclear reactors spray radioactive waste. Closed-cycle ones are too heavy, and messy if they crash land. Orion, the A-bomb powered spacecraft, was even worse in that regard. Still, if you launched from, say, halfway between Cape Horn and Antartica, where South Africa once tested an A-bomb without bothering anybody, it might work.
    • Antimatter propulsion. Dangerous, but feasible. Antimatter can be contained in electric and magnetic fields. Portable containers for antiprotons have been built. If anything goes wrong, all the energy comes out as gamma rays. Another one of those "the launch site had better be really remote" launch systems.
    • Laser launch. A big laser on the ground heats up water in the spacecraft to make steam. May be feasible for mini-spacecraft.
    • Antigravity. We have no idea how to do this. But it might not require new physics.
    • Beanstalks, tethers, etc. Requires really good materials in huge quantities, along with some other big-time means of space travel for the construction.
    • Winged launch. The Pegasus rocket was launched from a B-52, and souped-up fighters have made it to the edge of space. Helps the fuel problem a little, but not as much as is really needed.
    • Cheap, dumb boosters. The original Von Braun plan: mass-produce lots of cheap disposable rockets, build a big space station, and operate from there. Boosters have been mass-produced as ICBMs, but never got cheap enough.
    And that's the way it is.
  • I don't remember where, but I read an article a while about about buckytubes. The basic idea is a cylinder of carbon atoms with end caps in the shape of half of a buckyball. The interesting aspect is that creating them is relatively simple. Eventually, you end up with a pile of soot and some buckytubes. Well, they have enormous tensile strength and it had been suggested that they could be used in a space elevator (if they could be produced in large enough quantities).

    On an interesting side note, Clarke had originally written about a space elevator connected to a tiny island, but I can't remember the book (it was before 3001). I do recall that the island was conveniently very similar to Sri Lanka (where Clarke lives) but moved south to make the physics work.
  • No, a meteorite, according to the dictionary, is a meteor that reaches the surface of the earth without being completely vaporized, which might describe it after some enormous disaster (terrorist attack?) which brings it out of orbit and down on our heads. While in orbit, the appropriate terms would be asteroid, planetoid, moon (it's in orbit around the earth), or (possibly) moonlet (because of its likely small size).
  • Wouldn't it be cheaper to shield the space vehicle from gravity? It was mentioned in a show that I once watched on tv. I think the guy who came up with this was Eugen Plotnikov(?). He wanted to use rotating superconductors to reduce gravity IIRC.
  • AFAIK, teleportation has never successfully demonstrated, while antigravity worked in experiments (I'd prefer teleportation to my hotel at the moon, too). But then, it seems NASA is already working on this. I found the following links: A nice collection of antigravity links: http://www.eskimo.com/~billb/freenrg/antigrav.html NASA funds gravity shield: http://space.com/businesstechnology/technology/ant i_grav_000928.html AFAIK the spinning superconductors are not necessary anymore. A guy in the USA demonstrated antigravity with stationary superconductors already.
  • Sorry, I overlooked the /. stories on the issue of gravity shielding. They contain some good links.
    Anti-Gravity Research Confirmed
    http://slashdot.org/science/00/03/28/0815202.shtml
    NASA seeks to verify Gravity shield
    http://slashdot.org/articles/98/12/11/1236240.shtm l
    Practical Gravity Shielding for Spacecraft?
    http://slashdot.org/articles/00/03/28/2154213.shtm l
  • You are correct - we just need a monolith to make Jupiter _implode_ (it didn't explode/blow up remember - it contracted by all its gas being made into heavier chemicals, collapsed and became a star).
    Richy C.
  • Any one fancy a home under the ice at the Antartic then? Only used once by a certain John Wilson (read W.A.Harbinson's Projekt Saucer series for the background)..
    Richy C.

  • The Cheshire Cat wrote:

    An interesting article, but a little light on the details. There is a really good piece on how space elevators work here.

    The How Stuff Works link that Cheshire Cat provided is not that good -- it basically is a restatement of NASA's own page [nasa.gov] on their FD-02 Space Elevator concept, only with added ad banners. In addition, the How Stuff Works site attempted to set persistent cookies on my machine about 10 times before it gave up.

    In short: visit NASA's page [nasa.gov] and avoid How Stuff Works.

  • 10Gs would pretty much kill every human that took the ride.

    --
  • Most humans pass out at 6-7Gs. So I doubt that it would be an enjoyable ride if you did survive.

    --
  • No, than you would create an atmosphere on the moon!

    Why? Just because you have a tube running between the Earth and Moon (ignoring the problems with that, which are huge), you haven't repealed gravity -- which is what holds the air on Earth. The air in the tube's not going to decide to go somewhere else, just because you put a wall around it.

    ---

  • You are of course right -- there is shear stress from winds. But the original poster was arguing that it was the mismatch between orbital velocity and cable velocity at every altitude except geosynchronous orbit, which introduces shear forces. This just isn't physical -- it's based on a misapprehension of the problem, and this is what I was addressing in my reply.

    While there are aerodynamic forces on the cable, they're fairly small compared to the tensional forces, and can be managed by guy wires... just as with any tower.

    ---

  • High shear? From what?

    You put the bottom end on the equator, and the center of mass in geosynchronous orbit; the counterweight is above GEO. Then the "beanstalk" is in pure tension, with no shear at all.

    I think you're trying to put all the different parts into orbit, whereas only the GEO point is moving at orbital speed. Sure, the parts above and below that aren't (lower tries to fall down, upper tries to "fall" up) -- but they can't go anywhere because the structure holds them in a fixed relationship. In tension...

    ---

  • Actually, you've just done a great job of justifying the use of beanstalks tethers. Sure, at the moment we're materials-limited -- but notice the fact that we had a similar situation some 50 years ago with respect to the very computer technology you used to post your comment.

    There's nothing fundamental in the physics that prevents "space elevators;" it's just a materials problem. We'll get there soon enough...

    (As for your "big-time means of space travel for the construction" comment: we need one asteroid, which could be brought back by a robotic mission, and one minimum-strength tether line in geosynchronous orbit. Unreel that line in both directions, grab the lower end, and use that line as the first strand of the elevator -- you can run all the remaining structure up from the bottom, increasing capacity as you go. If capturing the asteroid at the right moment makes you nervous, you can drag the counterweight mass up the elevator too -- it just takes a little bit longer, and uses some more electricity.)

    ---

  • Let me assure you that the ideas aren't all mine -- a lot of work has been done on this concept, by a lot of people. Search Google for "tether space elevator" and have fun reading!

    About the outer endpoint of the system: typical designs use a large mass (like a small asteroid) at the outer end of the cable. Since it's beyond geosynchronous orbit but still moving around Earth once every 24 hours, it's going too fast for its orbital altitude; it therefore tries to move away from earth, but is kept in place by the cable. The result: enough tension to hold the cable "up." You select the tension by choosing the mass and its location relative to GEO. (Alternatively, you can make the cable longer to achieve the same result; but cable's expensive, while asteroids are relatively common.)

    To answer your question about connecting it to the ground: The proposals I've seen usually put a large "foundation" in the ground, and attach the bottom end of the cable to that. A rather similar thing gets done at the ends of a large suspension bridge: the cables at each end are pulling toward the center of the bridge, and must be anchored. I suppose an alternative would be to attach it to bedrock, but I think I'd rather engineer the attachment -- that way I would know exactly what it's capable of handling.

    ---

  • Re:What's the american degree for -1? (Score:3)

    by tesserae ( 156984 ) on Thursday December 28, 2000 @09:53AM (#1403934)
    Your idea isn't basically wrong, but it's an extreme case. What you can do is make life easier by changing the diameter of the cable to match the local loading: at geosynchronous orbit, where the loads are highest (because the entire cable is "hanging" from GEO, both inwards and outwards) the cable is largest, and it tapers down as it goes each way. This reduces the total weight of cable needed, and also reduces the necessary strength of materials by a huge factor.

    ---

  • The URL goes to the scond part of the article. See:

    http://www.space.com/businesstechnology/technolo gy /space_elevator_001226.html

    The reality in the article is next June's space tether experiment in generating electricity (using the power directly for spacecraft propulsion):

    http://www.space.com/sciencefiction/books/forwar d_ tethers_000328.html

    Of course the best known material to be strong enough for a space elevator turns out to be buckytubes...

    John
  • Let's assume for a minute that you have 1 "car" per km both up and down. This is 72,000 cars. Assume each car can hold 1000kg. This is 72,000,000kg on the elevator. Assume that it takes 4 days round trip. This means that every day you can move 18,000,000 kg. This equates to 36 million dollars a day. I'd assume that the payload per car would actually be higher, but I'm not sure. Yes a $1-$2 might be low. Even $100 though would be a LOT less than what we are paying now.

    Regardless, I think the real point is that unless we are moving a LOT more to space than we are today, then a space elevator is essentially non-useful.

  • The idea behind a space elevator is that it will be useful when we get to the point that we are shipping goods (and people) to and from space on a regular basis.

    Think of it this way: Which is cheaper: Riding an elevator to the top floor of a skyscraper or using a helicopter to do the same thing? A shuttle ride is around $22,000 per kilogram today. The estimates most people put on a space elevator is around a buck or two a kilogram.

    Today, there probably isn't enough practical use for this to justify the expense. In the future, especially when we start mining the moon and/or asteroids, this will become a big issue.

    Another point is that a space elevator can actually serve as the initial boost for interplanetary trips. The top end of the elevator is actually above geostationary orbit (the center of mass is at geostationary orbit - 35786 km) and as such when you figure the math using a conservative 36,000 km orbit, you get the fact that the top end is actually traveling well over 225 million kilometers in 24 hours or just under 9500 km/h (roughly 5900 miles/hour). This saves a LOT of fuel costs. You basically just wait until the right point and then "let go" and you're on your way to the moon, or mars, or....

  • Red Mars by Kim Stanley Robinson has an example based on a martian space elevator, where the tether is severed at the couterweight end.

    Short version: cable wraps itself around the planet a couple times, with the parts that were higher up hitting faster. Of course you have the friction of reentry as it comes back in to take into account, so the thing is fairly nasty. You end up not wanting to be anywhere near the equator when it comes down.

    Another interesting thing he brings up in a later book, Blue Mars, is a way to get around the tether point needing to be on the equator: Split the cable about 10,000 miles up, and have it tethered to 2 points eqiudistant from the equator. This opens up _lots_ of possibilities for where to put the thing, as opposed to being stuck right on the line.
    ---
    Your mouse has moved.
    Windows NT needs to be restarted
    for this change to take effect.
  • Finally a space article that didn't come from cnn [cnn.com]...

    Kudo's

    To bad Space Elevators are the Super Dense Optical Storage Devices of Space Industry. A Red Herring.

    suggested Space News Site's spaceflightnow [spaceflightnow.com]
    SpaceDaily [spacedaily.com]
    NasaWatch [nasawatch.com]
    SpaceWeather [spaceweather.com]
    Nasa [nasa.gov]
    It's ashame that SpaceOnline [flatoday.com] bit the dust and was absorbed by space.com [space.com], along with SpaceViews [spaceviews.com]

    If you want some real action become a Nasa click worker at http://clickworkers.arc.nasa.gov/top [nasa.gov]
    Maybe Slashdot will even do a story on it...

    I wait with herring baited breath
  • Considering the kinds of mass destruction that can be wreaked on the rest of the work from orbital heights means that this would not only be the space elevator, it would also be a major weapon.

    Kim Stanley Robinson demonstrates the destructive potential of this type of elevator excellently in his book Red Mars. In the story, someone blows the orbiting "counterweight" off the end of the cable. Without the large mass in geostationary orbit to keep the cable straight, it basically falls over, wrapping around the planet a couple times in the process and flattening everything in its path. And everything nearby, since by the time the upper half hits the ground, it's travelling many times the speed of sound, packing quite a shock wave in front of it.

    Pretty scary stuff.

    --

  • Assuming this beast gets built, we have to keep in mind that at first (and, I think, for a very long time) there will only be one of these things.

    Its cost effectiveness (and it's appropriateness for use by individual private passengers) must take into account the cost of transporting the people and cargo across land to the site of the tether.

    I have no idea how to crunch these kinds of numbers. Has anyone else done so?

    --

  • make the tube long enough to the moon and you could get a vacuum!
  • It's technically possible to affect the Earth's motion by making it woble, but it would require so much more mass than they're talking about that it is not worth mentioning. The moon has 1/6 the mass of the Earth, and its effect on our orbit is just sufficient to cause us to have tides. Depending on where the elevator was placed, it could augment or suppress the tides, but only if it was a significant fraction of the mass of the moon.

    -- ShadyG

  • Why not just use Shadow Square wires?

    -- ShadyG

  • I've been reading about how astronomers want to deploy new space telescopes over the next 15 years or so so that they can search for new planets optically. Obviosly this takes stronger telescopes than we have been using. What I am curious is if any current telescopes could pick up any megascale engineering constructs such as a Ringworld? I know no one would ever get the funing to go looking but it might be cheaper/easier to look for some of them than to look for planets.
  • I remember reading a few weeks ago (I forget where, it was a link from the last space elevator story) that right now we have the tech to make a 1 mile high skyscraper, there just is no economic incentive. So I could definitly see 31mi. in the next 50-100 years. All it takes is one advance in building materials. And if you think that is unrealistic, look what easy to manufacture steel did to the size of buildings, they went up by at least a factor of 30 in 50 years I would think.
  • Do you mean the counter-weight that is used to make lifting an elevator easier? (Sorry, I don't know too much about elevators).
  • Isn't the point of this to provide a quick/cheap launching platform for space going vehicles?

    It's (theoretically) much, much less expensive to launch from space than it is to launch from the planet's surface. It's possible that something like this could make the use of local space cost-effective.

    Holidays on the moon, somewhere to bury nuclear waste, strip mining and no complaints from the neighbours. Heavy industry could move up there and not worry about polluting the atmosphere - there isn't much of one anyway!

    Makes you think doesn't it?


  • but, take the thought experiment to the extreme, if the tube was long enough and extended far enough into space, and you could initially fill it with air, would it not act as a siphon? But, in regards to the initial question, the air in the tube doesnt know, and isnt acted upon by any additional forces, then the air right next to it on the outside of the tube.

  • actually, after thinking it through, it wouldnt end up like a siphon, the air inside the tube at the far end would either escape, or get pulled down, until the conditions in the tube matched the outside of the tube, like a big barameter.
  • Serious question: Wouldn't such a thing affect the earth orbit?

  • Cool as this is, think about physics and politics (Score:3)

    by human bean ( 222811 ) on Thursday December 28, 2000 @09:18AM (#1403961)
    As anybody working in the fields of mechanics and material science can tell you, this is a lot farther off than it looks, folks. Just the logistics of flying the orbiting mass (yes, flying, you maybe though satellites stayed up there without guidance and thrust?) twenty-four by seven FOREVER (with what this puppy has to mass, believe me, you don't want this thing's orbit to degrade, ever.). Using a little thought and imagination, the list of "safety related" items goes on and on.

    Also, the thought of having one doorway to outer space, under the control of some political force or another, does not strike me as safe. Considering the kinds of mass destruction that can be wreaked on the rest of the work from orbital heights means that this would not only be the space elevator, it would also be a major weapon. Lets face it, once something is in orbit, landing it in a particular spot is not that difficult. For those who do not believe, go get a copy of Navigation for Space Flight, by Prentiss Hall, I think (it's been a while). At the kind of energy levels we are talking about here, you don't have to be precise.

    Besides, I want my OWN fricking orbital shuttle. I've got places to go besides Clarke orbit.

  • The purpose of this elevator is not to go up magcially by itself. The point is the following: rockets have to carry their own weight plus the weight of the propellant which is unfortunately the largest percentage. An elevator just needs a motor to pull itself up. You could even imagine an elevator with solar panels to slowly climb its way up by grabbing th cable. Apparently these poeple propose the "pulling" to be done with magnets but the principle remains the same.

  • Megascale Engineering (Score:5)

    by tamnir ( 230394 ) on Thursday December 28, 2000 @12:08AM (#1403965)

    If you are found of Dyson spheres, beanstalks, spacehooks, terraforming and other stellar husbandry, check out the following site, full or ressources on these topics:

    Megascale Engineering [aleph.se]

    Megascale engineering is about building/creating or using structures on a extremely large scale, at least 1000 kilometres in diameter, often incorporating highly advanced and/or speculative technology. Typical examples are orbit-to-ground Beanstalks, moving planets, Dyson Spheres and Stellar Husbandry.

  • There has to be a practical reason... (Score:3)

    by Gendou ( 234091 ) on Wednesday December 27, 2000 @11:57PM (#1403970) Homepage
    Sure, Arthur Clarke's vision of an artificial ring around the earth is a great idea, but it's a bit far off.

    And this wouldn't really be a step in the right direction. Sure, research into new materials/engineering techniques would be fruitful, but what is this really?

    An elevator to nowhere. Imagine how silly it'd look. :-)

  • How you can forget that Gravity decays at the square of the distance? Do you know what is angular momentum? And how can you dare to think about something pushing this elevator up in vacuum, by itself. Hey, as anyone forget Newton's Third Law? Sorry to be so flamously bitter, but do they still teach it on school?

    The third one? That'd be the one that proves reaction rockets are impossible, right?

    "As a method of sending a missile to the higher, and even to the highest parts of the earth's atmospheric envelope, Professor Goddard's rocket is a practicable and therefore promising device. It is when one considers the multiple-charge rocket as a traveler to the moon that one begins to doubt ... for after the rocket quits our air and really starts on its journey, its flight would be neither accelerated nor maintained by the explosion of the charges it then might have left.

    "Professor Goddard, with his "chair" in Clark College and countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react ... Of course he only seems to lack the knowledge ladled out daily in high schools."

    -- New York Times Editorial, 1921
  • Wasn't it the huge diamond at Jupiter's core that gave the 'ring around the earth' the tensile strength required?

    All we need to do is find a bloody big diamond, or gain control of matter at the molecular level.

    Or Jupiter can blow up. That would work as well...
  • I'm not sure I understand what you mean. The "lower elevations" would of course be too slow with respect to their altitude to maintain orbit by themselves and hence would feel some weight down. (Conversely, the counterweight above GEO would be too fast, and feel some weight up.) That's why you need its center of mass at GEO (so the whole structure is in orbit) and a hell of a tensile strength!

    Incidentally, the title of the article, "Next stop: low Earth orbit" is misleading: the only point in the tower where you can drop off and be in orbit with a little push is at GEO.

  • From the top of my mind I can think of 3 main reasons that have driven science all along history: Practical Reasons, wars and humankind endless curiosity. I guess that for every advance in science we can find a bit of each in it. Reasons for the elevator? Practical: Cheaper and safer launch platform for communication satellites, elevator for the first space tourists, cheap way to send labor to orbit. Wars: Easy and fast way to put spy satellites in orbit, transfer funds from launching to R&D, build an orbital defense/offense system, space wars. Curiosity: A challenge, a step forward towards space colonization, a way to find new questions. Pick the one you like most Personally I like to think that the third is what drives us... but I'm naive

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