March 27, 2002

9:49 PM

"Even though the challenges to bring the space elevator to reality are substantial, there are no physical or economic reasons why it can't be built in our lifetime."

Once just a cool sci-fi idea dreampt up by Arthur Clarke, Space.com reports that a 62,000 mile ride is not only possible, but probable. And cheap at only a couple hundred bucks per pound.
posted by tsarfan (37 comments total)

this is very cool.
posted by o2b at 10:00 PM on March 27, 2002

Wonderful idea. But 62,000 miles is a long trip for the casual space tourist. How fast could vehicles go on the fiber? Even at 200 mph, that's still a trip of almost two weeks each way. Probably speeds could increase dramatically outside the atmosphere, though. Of course, the faster you go, the greater proportion of your trip you have to spend slowing down.

For an example of the space elevator in fiction, see the final episode of the six-part anime series Gunbuster. Two characters ride one into space, with no mention of the technology: they simply board a vehicle which looks suspiciously like a Japanese bullet train, which travels a thin ribbon up into the sky. Eventually they arrive at a space station.
posted by Slithy_Tove at 10:14 PM on March 27, 2002

Slow is fine for freight, though.
posted by pracowity at 10:29 PM on March 27, 2002

Yep, and you don't have to worry about slowing down if you're using it to get into orbit. By the time you go zipping off the far end and into space you'll have picked up a respectable velocity, depending on how its built.
posted by bshort at 10:31 PM on March 27, 2002

This reminds me that elevator in The Simpsons that just goes really really high, but ultimately nowhere and just drops the people. Literaly.
posted by jmd82 at 10:34 PM on March 27, 2002

what if we could make it look kinda like a giant monolith extending into space? maybe then we could find some way to speed up the earth's rotation at will so we can use the space elevator as a kind of cosmic baseball bat to swing at whatever dangers drift our way. even if isn't a practical or necessary thing to do, we should do it anyway! because space bats are cool!
posted by mcsweetie at 10:44 PM on March 27, 2002

No point mentioning those bats, I thought. The poor bastard will see them soon enough.
posted by pracowity at 10:48 PM on March 27, 2002

A space elevator was pretty well described in Kim Stanley Robinson's Red Mars too, and it became an important part of the plot.
posted by bragadocchio at 10:51 PM on March 27, 2002

"I'm looking at a business plan that shows some investor could triple his or her money in about 6 years, and the initial investment could be as low as $5 billion," Edwards said.

If this is true then someone will build it. Excellent.
posted by homunculus at 10:53 PM on March 27, 2002

There's a funny analysis of the practicality of this at nano magazine. Also, while searching, found the Omega-pedia of technology memes - neat.
posted by vacapinta at 10:55 PM on March 27, 2002

mcsweetie + pracowity = big funny
posted by Optamystic at 11:25 PM on March 27, 2002

I remember reading a physics analysis of this idea a while back which indicated that if terrorists were to snap the elevator cable, the consequences would be catastrophic (as in "lets set off some themonuclear bombs across the globe" catastrophic). However, I can't find the reference. Any physics majors out there want to calculate the consequences for us?
posted by tdismukes at 6:27 AM on March 28, 2002

i seem to recall heinlein mentioning some sort of space elevator-thingy in Friday...

if someone built one of these we could go on vacation!
posted by s.carrier at 6:35 AM on March 28, 2002

tdismukes: I read the same thing. Something about the cable falling back to earth. In addition, I don't think any material is strong enough to withstand the stress.
posted by quirked at 6:36 AM on March 28, 2002

The space elevator in Kim Stanley Robinson's books was taken directly from "The Fountains of Paradise." The name of the station that held the cable was "Clarke."
posted by Loudmax at 6:40 AM on March 28, 2002

Quirked - I'll bet that it's close. Most of the cables in the different books I've read have been built out of carbon fiber. Many of them were built by nanoconstructors, but then again, that's science fiction - it's very possible to do it without by simply 'growing' the cable down from a space station, which is how it woul have to be built anyway...

tdismukes: Yes, that's part of the plot of Kim Stanley Robinson's Red Mars... they blow the cable at the station, and it falls down and wraps itself around the planet. You would have to sever the cable in space though, and I'll bet that a structure that would be capable of supporting its own weight or acting as a track for cargo trams would be a little harder to sever than just building/buying a bunch of nukes and setting them off around the globe would be.

One of the things I like about this idea is the economic boost (no pun intended) it would bring to the mostly poor eqatorial nations where the cable could be situated. Also, with a 2 week train ride, it -would- be possible for everyday people to get into orbit, and all space-bat jokes aside, it gives us a good base of operations for actually expanding into space as a culture... something that all the rockets in the world wouldn't be possible of building.

As an aside, I'll make a bet that the chinese will be the first nation to actually construct one. I'd actually be willing to put money (with interest... ;) ) down on a space elevator being the eventual goal of their space program.
posted by SpecialK at 6:51 AM on March 28, 2002

A few points.

Once the cable is paid for, the costs of travel drops to a few cents per pound. You use linear induction motors to lift -- which act as brakes and generators on the way back down, recovering most of the energy. That, and a few salaries, will be your only running costs. The construction costs are huge, of course.

Two, you'll only go slow at the very start of the lift. As you clear the lower atmosphere, drag falls. Through most of the lift/drop, your speeds will be in the thousands of miles an hour. (200mph/26000 miles to geosync would be 130 hours to orbit, or twice that to the anchorage, assuming a symmetrical cable.)

Third, the cable would be in tension. If you see someone attempting to sever the cable (which will be hard,) all you need to do is detach it from the bottom, and it'll fly away. (It has to be -- there's no foundation on Earth that can support the cable in compression.)
posted by eriko at 6:56 AM on March 28, 2002

Eriko's right... severing the cable from the bottom's kind of a "so what?" prospect... the real danger is destroying or damaging the space terminus of the cable.
posted by SpecialK at 7:22 AM on March 28, 2002

What kind of music will they be playing in this... uh... elevator?

::runs and hides::
posted by kahboom at 7:37 AM on March 28, 2002

It sounds like a giant beanstalk to me...
posted by spilon at 7:39 AM on March 28, 2002

Also recognize that the elevator wouldn't have to go all the way to the top. There would still be a need to service low earth orbit, just a couple of hundred miles up. Once you get there, the only problem is speeding up from around 1000 mph to the orbital velocity of roughly 16000 mph. Difficult, but not impractical.
posted by dhartung at 7:44 AM on March 28, 2002

Once you get there, the only problem is speeding up from around 1000 mph to the orbital velocity of roughly 16000 mph. Difficult, but not impractical.

This is an enormous problem because it isn't just a matter of getting to the right elevation then rocketing off at the right orbiting velocity. There will have to be a continuous increase in angular momentum of the ascending body as it goes up or else the cable will "drag" and the space terminus will fall into lower and lower orbits until it collapses. The big misconception about the elevator is that it forgoes the need to have expensive rockets propelling you to a high 'lateral' speed (I mean paralell to the earths surface I guess). That will still be required! It will just have to be worked into the added complexity of ascending a static column. Like most transportation devices (cars, trains, planes) most of the cost will be energy input and the cost won't come down much until better energy sources are realized.

The cost of lifting the initial cable material will be astronomical (pun intended). Think about the cost of laying 62,000 miles of freeway (which costs about $1,000,000/mi) and that's just a bunch of cheap ass concrete and tar that lays on the ground. This elevator would be made of expensive materials that have to be lifted into space the old-fashioned way!

I don't see a future for this idea.
posted by plaino at 8:32 AM on March 28, 2002

I wonder how conductive this carbon tube stuff is. Seems like with the entire atmosphere swirling around up there, you'd build up an enormous difference in potential between the top and bottom. Guess you could just add a 62,000 mile metal lightning rod / ground strap.

And how about throwing in a little sympathetic resonance? It would be the ultimate bass string.
posted by groundhog at 8:57 AM on March 28, 2002

The cbc has a good audio story about the elevator. Bradley Edwards has a lot of good thinking about it, and he lives in my town. Wonder if he needs a summer intern...

Re: building a freeway to space -- you start with a very, very thin and light cable. You then climb that carrying a thicker cable, and so on.

Re: climbing -- the climbers use eletric engines powered by photovoltaic cells. Rather than using the sun, however, they get their energy from a earth based low intensity laser.
posted by daver at 9:28 AM on March 28, 2002

Plaino - Three words: Geostationary Equatorial Orbit. Not a huge problem, although keeping something that large geostationary presents interesting computational and load-balance problems.

Anyway, you've gotta drop the cable down TO the earth from something that's already in a geostationary orbit. Most concepts I've seen have involved capturing a carbonaceous asteroid to one of the LaGrange points and forming the carbon-strands out of it.

You're right about the cost. Definately into the billions, and we'd have to have a way of getting trained laborers into orbit to at least build a LEO station to drop the cable to earth. Once they can get elevators up to the most-likely primitive LEO station, they can start to build a more advanced LEO station or continue onto HEO. The logistic problems and the construction order are actually fascinating to consider.
posted by SpecialK at 9:30 AM on March 28, 2002

I'd be worried about those Vermicious Knids.
posted by Skot at 9:45 AM on March 28, 2002

Geostationary Equatorial Orbit. Not a huge problem, although keeping something that large geostationary presents interesting computational and load-balance problems.

This _is_ what I was talking about. As you raise something up a vertical path emanating away from the earth, including at the equator, you are adding angular momentum to it. The energy to do that has to come from somewhere and if it does not then the cable will be dragged. If the 'cable' was rigid like a long stick then the requisite energy would be transferred out of the upward thrust but that only works if the entire 62,000 miles is rigid (which would be impossible). It would be cheaper and mechanically simpler to raise an object up a virtual column using computerized thrusters to keep it on internally simulated track. Of course that's essentially what we do now with conventional rockets...
posted by plaino at 10:01 AM on March 28, 2002

as much as i love arthur c. clarke, he didn't originate the idea for a space elevator. this article details the history of the idea.
posted by jimw at 10:11 AM on March 28, 2002

The big misconception about the elevator is that it forgoes the need to have expensive rockets propelling you to a high 'lateral' speed (I mean paralell to the earths surface I guess).

Nope. The anchor of the elevator is in an long orbit (or a solar orbit!) but it's held into geosynchronous orbit by the tower itself. The centerpoint of the tower will travel in the exact same orbit (and at the exact same speed) as a satellite right next to it in geosynch orbit. The tower is held at tension by a large mass on the very end, thus, the tower only bends a little bit. Let go of something at the midpoint, and it's in geosync. You will need some thrust, otherwise, everything just hangs around the tower, but it's tiny amount of thrust compared to the thrust you need to get the satellite into that orbit in the first place.

You could, if you perfectly balanced the tower, get it to hover just a couple of feet off the ground, but other influences (the Moon's and Sun's gravity would be the largest) would quickly alter the tower's orbit. Unbalancing the tower so that it tends to fly away is the safer bet -- since you are looking at masses that may reach a large fraction of a pentagram.

And you *do* want to be able to go all the way up -- the very end of the tower, in supra-geosync orbit, will be travelling well beyond Earth's escape velocity. Let something go, it's in a solar orbit. This is a big win if you want to go to anywhere else in the solar system -- climb the tower, build the ship, and you've save over 95 percent of the fuel you'd need to get the ship to that orbit from the ground. This make moon travel not only practical, it makes it cheap -- there would be times where you can just let go, and the ship would float to the moon without thrust. (Better have an engine to get into lunar orbit, though.)

This one's long. I'll start another....
posted by eriko at 10:13 AM on March 28, 2002

Building the tower is tough. It can't hold it's own weight in compression, so you have to build from the top down. But you can't do that, since the anchor mass wants to fly away. So, you start in geosynch orbit. Fly a big carbon rich asteroid into geosync, and start building. To keep it in geosynch, you have to keep the center of mass in same place, so you build both up and down at the same time. The tower grows both down to and away from the earth, at the same rate.

Once you get close enough to start feeling atmospheric drag, you stop, and reel down a landing line -- while reeling out a balance line with a small mass attached. By reeling these lines in and out, you alter the center of mass, thus, the orbit. You touch the landline down, anchor it, then unreel the balance line until the tower is taut. This fixes the tower down. You then restart building the tower proper, and build it to the ground. Once you anchor the tower proper, you replace the balance line with an anchor mass, build the induction motors and tracks, and open for buisness. Build a large station on the remnants of the centerpoint asteriod, open a bar, and there would be the Best. MeFi Gathering. Ever.
posted by eriko at 10:21 AM on March 28, 2002

Eriko,

You are just restating the misconception. You can't design away the angular momentum problem. Regardless of the design, YOU HAVE TO ADD ANGULAR MOMENTUM AS YOU ASCEND OR THE THE ELEVATOR WILL DRAG. If the elevator shaft is rigid (regardless of how it is kept rigid) the drag will be transferred to the vertical motion of the ascending object thereby taking the energy required for lateral acceleration from the energy applied to vertical acceleration. In this case the object will act as if it is much heavier than it really is!

BTW the geosynchronous asteroid idea is idiotic in the extreme.
posted by plaino at 10:51 AM on March 28, 2002

You guys!
posted by y2karl at 11:18 AM on March 28, 2002

Even more interesting article here . The author discusses space hotels and space elevator design, including a bunch of references.
posted by daver at 11:48 AM on March 28, 2002

(setq Frink T)

You do have to shift angular momentum to keep the system at equilibrium, but that's easy to do. Simply have two cabs, linked, one running from ground to geosynch, on running from geosynch to anchor. Total mass, and energy, and angular momentum stays identical. The only energy spent is overcoming the gravitational differential between the earth-geosync car and the geosynch-anchor car (as well as frictional losses.) You don't even need cables to link them -- just have the motors move the two masses in opposite directions at the same time. With twin track linear induction motors, you'll see one track on the rising car with more resistance -- and the opposite track of the falling car generating more power. Cross connect, and the problem dissappears.

And it's a minor problem. You've got 22,000 miles to induce this momentum -- you don't have to go straight up, then horizontial. We're talking a few newtons of force at a time -- hell, just *burn the power* to correct. If you've got the power to build the tower, you've got more than enough to run the cabs.

The asteroid in geosynch is the *only* way to build the tower. Why is it "idiotic in the extreme?"

There are only three holdback to the tower as we know it.

1) We can't do large scale construction in orbit. Yet

2) We don't have a material to build the tower. Yet (carbon nanotubes might be it, though)

3) It'll cost more money than even Mr. Burns has. Much less most countries. One Trillion USD might do it. We have the money -- but it'll be a huge change in our economy if we spend it (That's 1/10th of the entire GNI of the US in 2000.)

(setq Frink NIL)
posted by eriko at 11:52 AM on March 28, 2002

Eriko,

Your balancing angular momentum system is feasible only if you never leave anything in space. In other words once the balancing body has moved inward to compensate for something brought into orbit something else would have to be sent back to earth to compensate the resetting of the balance for the next trip from earth. Therefore, it would still be a poor method to bring things into orbit. At best it would be good at exchanging old satellites for new.

As for the asteroid you've got to be kidding!

Asteroids travel at extraordinary speeds. Your scheme would require us to send a vehicle carrying a team of workers and a bunch of rockets to the asteroid, assemble the rocket apparatus, then 'fly' the asteroid into orbit. All this assumes a suitably large and carbonaceous asteroid is nearby. And nearby, in this case, would mean between here and Mars which is pretty damn close! If an asteroid gets that close it's usually front page news about a near-miss collision. If your statement: "The asteroid in geosynch is the *only* way to build the tower." is true it is equivalent to saying: "The tower is not humanly possible."
posted by plaino at 1:22 PM on March 28, 2002

there were terrorist attacks on a space elevator in this book also, i think it was on the ground i don't remember. i believe it was in the 3rd or 4th of the series. they are good anyway, if you like sci-fi. the plot isn't centered around the elevators though
posted by rhyax at 2:46 PM on March 28, 2002

Therefore, it would still be a poor method to bring things into orbit. At best it would be good at exchanging old satellites for new.

No. You load it at the bottom, fling it off the top. This imparts a slight outward velocity, which, since the tower is tethered to the planet, changes the earth's orbit by an incredibly small amount. (True of any sat launch, as a matter of fact.)

Remeber, we're talking millions of megatonnes of mass in the tower -- a few hundred thousand kilos won't affect it's orbit noticibly, and won't affect Earth's orbit at all. What torque you do get from unbalanced cars can be taken care of by the mag levs. Occasionally, you adjust the mass of the anchor, if need be.

(The scale of the tower is hard to get used to. This thing is *huge* beyond words.)

Asteroids travel at extraordinary speeds. Your scheme would require us to send a vehicle carrying a team of workers and a bunch of rockets to the asteroid, assemble the rocket apparatus, then 'fly' the asteroid into orbit.

Yes. Exactly. This is, in fact, an easier proposition than building a tower-- simply put a rocket and fuel on the asteroids, and change the orbit. In fact, a comet head would be a better bet than an asteroid -- it has all the fuel and oxidizer you need. But if we have the tech to build the tower, moving asteroids around is trivial. In fact, catching an earthgrazer is a good tech to develop anyway -- what if that earthgrazer is an earth hitter?
posted by eriko at 4:35 PM on March 28, 2002