Building a space elevator would stimulate the economy

[Dilton Doiley,Philosopher King]

It's a wonder why we aren't doing it already. Not only would it create a ton of new jobs to build the thing, it would promote stellar research, nano research and space research, just off the top of my head. And surely it would increase international trade...

...why aren't we doing it? Did the stimulus bill include funding for this?

[begbert2]

Do we actually *need* a space elevator?

[The Batman]

It's not in the stimulus package, or in the new budget.

I doubt it will be in any future stimulus packages or budgets until we are way over this recession.

[Chronos]

I'm as big a fan of the Space Elevator as anyone, and I honestly think it'll happen in my lifetime. But the time is not now: The technology for making carbon nanofibers isn't yet where it will need to be, and none of the rest of the project can go forward without that. So all we'd be stimulating right now (when the stimulus is needed) is those people working in that specific area of research.

The great thing is, though, carbon nanofiber is a promising area of research even without the Space Elevator. People are going to develop cheap ways to make them, if only to use them to make golf clubs and fishing lines. Let the research continue, and once we do have the nanofiber golf clubs and fishing lines, and maybe a suspension bridge or two, then we can bring the Space Elevator onto the front burner.

[Bryan Ekers]

I sat through an interesting presentation at a sci-fi convention last year in which the speaker (who had some fairly-decent space-buff credentials) pointed out that if we had some kind of super-light super-strong material such that we could build a space elevator, we could more easily use it to build super-light super-strong launch vehicles. So, space elevator (estimated cost: $infinity trillion) or ten million Saturn-sized rockets, each several orders of magnitude more efficient than existing designs (estimated cost: $a bunch)?

[mswas]

Well there is the fact that it would be super expensive. Also, have you ever seen what a taut cable does when it suddenly snaps? It uncoils and whips around like an angry snake. Do you really think that is a good idea with a 500 mile long cable?

Bryan: I think the ideas of Buckminster Fuller will be applied at the nano-scale in materials a lot more, and we'll be seeing those materials start to appear within the next twenty years. I expect another major space push by mid-century. People will capitalize on the 100 year anniversaries of everything in order to gain funding for projects.

[Tenebras]

Not to nitpick here, but it's not a cable 500 miles long. It's a cable 90,000 miles long. Ninety thousand miles long.

As long as one billion dollar bills laid end to end, so if we could figure out how to make it out of dollar bills it would only cost one billion dollars--off to the drawing board!

[Voyager]

Not only don't we have the material yet, we don't have the launch capacity to get all the material into orbit, or to build the major construction site there that we'd need to build it. it has to be in synchronous orbit, remember, which is a lot further out than where the shuttle goes now. The best thing you can do for this is NSF funding for the materials and getting a decent launch vehicle.

[Spoke]

Wait, aren't carbon nanofibers carcinogenic? That would seem to be a stumbling block.

[Bryan Ekers]

Wait, aren't carbon nanofibers carcinogenic? That would seem to be a stumbling block.

So build it in Mexico.

[mswas]

Not to nitpick here, but it's not a cable 500 miles long. It's a cable 90,000 miles long. Ninety thousand miles long.

As long as one billion dollar bills laid end to end, so if we could figure out how to make it out of dollar bills it would only cost one billion dollars--off to the drawing board!

Oh good so it can wrap around the planet a couple times while it's whipping aroudn like a snake. ;)

[RickJay]

There isn't enough money in the world to build a space elevator, and half the technology to construct and operate it isn't worked out yet.

Since there's really no chance at all that such a thing could be constructed in our lifetimes - sorry, Chronos, it is not going to happen - you would probably get much more effective stimulus by simply dropping bales of money out of helicopters flying over low-income neighborhoods.

[mswas]

So build it in Mexico.

Lots of things we use everyday are carcinogenic. We can encase carbon nanofibers so that they don't blow around like dust. Just coat the structure with some kind of polymer resin.

[billfish678]

Not to nitpick here, but it's not a cable 500 miles long. It's a cable 90,000 miles long. Ninety thousand miles long.

As long as one billion dollar bills laid end to end, so if we could figure out how to make it out of dollar bills it would only cost one billion dollars--off to the drawing board!


To be fair, not neccessarily IIRC.

I seem to recall proposals for such things that are like big spoked wheels that orbit the earth, with the tips of the cables droping down into the upper atmosphere.

Not that that would be remotely easy either, but at least the cables are only hundreds of miles long instead of tens of thousands.

[Chronos]

I sat through an interesting presentation at a sci-fi convention last year in which the speaker (who had some fairly-decent space-buff credentials) pointed out that if we had some kind of super-light super-strong material such that we could build a space elevator, we could more easily use it to build super-light super-strong launch vehicles. So, space elevator (estimated cost: $infinity trillion) or ten million Saturn-sized rockets, each several orders of magnitude more efficient than existing designs (estimated cost: $a bunch)?We already have a material which is plenty light and strong enough to build rockets out of... It's called aluminum. The weight of the hull of any rocket is negligible compared to the weight of the fuel-- That's the reason it costs so much to launch anything into orbit on a rocket. A space elevator bypasses that requirement.

There isn't enough money in the world to build a space elevator, and half the technology to construct and operate it isn't worked out yet.The cost estimates I've seen are in the vicinity of 50 billion dollars. A government could easily afford that.

Oh, and as for the "what if it breaks" argument, in that case it would burn up in the atmosphere before hitting anything on the ground. We'd be out our initial investment, of course, but it wouldn't be a cataclysmic global apocalypse.

[Kinthalis]

you would probably get much more effective stimulus by simply dropping bales of money out of helicopters flying over low-income neighborhoods.


This. I want this done. In fact, if you want to test this hypothesis out I personally volunteer my neighborhood for the test trial.

[The Batman]

Oh, and as for the "what if it breaks" argument, in that case it would burn up in the atmosphere before hitting anything on the ground. We'd be out our initial investment, of course, but it wouldn't be a cataclysmic global apocalypse.

Besides, most designs seem to call for the elevator to be anchored either on an island or a refitted deep-sea platform so the risk of miles of cable plummeting to the ground isn't that big anyway.

[Quartz]

A space elevator wouldn't actually touch the ground directly anyway. The bottom end would be a very short distance above the ground and 'held' by something. The reason for this is to prevent vibrations from earthquakes and the like.

[smiling bandit]

Besides, most designs seem to call for the elevator to be anchored either on an island or a refitted deep-sea platform so the risk of miles of cable plummeting to the ground isn't that big anyway.

Plummeting straight down isn't the issue. It's what happens if it starts wrapping that becomes a problem.

[RaftPeople]

There was a recent article (somewhere? might have been a link on slashdot) about a study that concludes there would be a requirement for thrusters to stabilize the cable. This adds a new dimension to the complexity of the project.

[Tenebras]

To be fair, not neccessarily IIRC.


Indeed, you can hang a counterweight on the space side and make the cable shorter. However, the idea only works if you are in a geostationary orbit, which means that you need to be at least 22,236 miles above the surface of the Earth. You also have to lift a massive counterweight into orbit. (In fact, the center of mass needs to be above geosynchronous orbit, so it's actually longer than that...)



The cost estimates I've seen are in the vicinity of 50 billion dollars. A government could easily afford that.

Oh, and as for the "what if it breaks" argument, in that case it would burn up in the atmosphere before hitting anything on the ground. We'd be out our initial investment, of course, but it wouldn't be a cataclysmic global apocalypse.

Who says it will cost $50 billion dollars? The Apollo program cost $25 billion dollars back in the 60's and 70's. That's $125B dollars in today's money.

The mass of the cable is extremely sensitive to the density and the strength of the material you build it out of. Even if you have magically strong and light buckytubes, you're still looking at around 13,000,000 kg of the stuff. And the smallest cost I've seen for a gram of the stuff is $25. So we're talking about $300B just for the raw materials.


Worrying about what happens when it breaks is actually a fool's game, because if you can build it, you already have an army of wizards on your payroll. Just have one of them magic it back together the same way they magicked it into being in the first place.

[Tenebras]

There was a recent article (somewhere? might have been a link on slashdot) about a study that concludes there would be a requirement for thrusters to stabilize the cable. This adds a new dimension to the complexity of the project.

It's because the orbit it's in isn't stable.

Another problem to solve are the thermal issues. It's an enormous cable which is spending part of its time in sunshine and part of its time in the dark.

Oh, and oxygen tends to destroy the nanotubes.

[Monster104]

Who says it will cost $50 billion dollars? The Apollo program cost $25 billion dollars back in the 60's and 70's. That's $125B dollars in today's money.
NASA estimate from 2003 (http://www.niac.usra.edu/files/studies/final_report/521Edwards.pdf) was ~$10 billion to build one over 15 years, with technical costs around ~$6.5 billion.

And Japan thinks it's doable (http://www.isn.ethz.ch/isn/Current-Affairs/Security-Watch/Detail/?lng=en&id=93730). And here's a list of cost estimates. (http://spaceelevatorwiki.com/wiki/index.php/SpaceElevatorCost)

[BrainGlutton]

There is a company (http://en.wikipedia.org/wiki/LiftPort_Group) floating the project but it ain't doing so well.

[billfish678]

Just my semi-technical opinion....

The cable breaking presents no real danger to anyone, besides of course the people very close to it or on it.

It would be quite spectacular visually and one hell of a disaster financially, but as any kind of threat to the general population? ....meh....next worry please...

[BrainGlutton]

Just my semi-technical opinion....

The cable breaking presents no real danger to anyone, besides of course the people very close to it or on it.

It would be quite spectacular visually and one hell of a disaster financially, but as any kind of threat to the general population? ....meh....next worry please...

There is a megadistaster scenario plausibly portrayed in Ben Bova's novel Mercury. (http://en.wikipedia.org/wiki/Mercury_(Ben_Bova))

[CutterJohn]

One thing to remember about a space elevator is you do not need the entire mass of the cable up at once. Remember to build a suspension bridge.. Shoot a small cable over to the other side, then pull the rest of the cable across.. Now, likely it would be impossible to pull the cable up with a smaller one, but construction materials could be pulled up.

So you don't need to get a lot of the millions of kg of material into space right off the bat using normal, innefficient rockets.


Personally though, I think a launch loop (http://en.wikipedia.org/wiki/Launch_loop) is a much more feasible idea.

[gladtobeblazed]

How hard would it be to destroy this thing? Could a single madman/terrorist bring the whole thing down with a small plane? Or would the strength of the cable be sufficient to withstand that kind of impact?

[Lumpy]

The cable doesn't have to be a massive thick structure. In fact the proposals for the first generation cables are for a cellophane-thin ribbon which can still hoist several tons at a time. The mass to be boosted to geosync orbit thus becomes workable. If it broke, what didn't burn up on impact with the Earth's atmosphere would float down like confetti. In that sense, the concept is scalable- you can start with a small one and only expand once the bugs are worked out.

[Tenebras]

NASA estimate from 2003 (http://www.niac.usra.edu/files/studies/final_report/521Edwards.pdf) was ~$10 billion to build one over 15 years, with technical costs around ~$6.5 billion.

And Japan thinks it's doable (http://www.isn.ethz.ch/isn/Current-Affairs/Security-Watch/Detail/?lng=en&id=93730). And here's a list of cost estimates. (http://spaceelevatorwiki.com/wiki/index.php/SpaceElevatorCost)

The "NASA Report" is a study that was apparently funded by NASA through a child organization meant to showcase big ideas for the future. The budget rundown was made by the same guy, Brad Edwards. The estimate on the spaceelevatorwiki and in the 2003 report seem to use the same data. I call your attention to the part of the table where he accounts for the cost of the cable itself at $75M. This figure is arrived at by taking 750,000 kg of CNTs at $100/kg. Where does the $100/kg figure come from? In 2003, someone at the Mitsui corporation told Dr. Edwards that Mitsui would be producing 10 tons of CNTs per month at a cost of $100/kg.

Of course, the lowest actual price yet recorded is $25 per gram. Using this as our cost for the cable (not of actually building the cable, just collecting the stuff we're going to build it out of) we have a cost of around $19B for the cable. The rest of the numbers also appear to be just stuff he pulled out of the sky.

[Little Nemo]

Wait, aren't carbon nanofibers carcinogenic? That would seem to be a stumbling block.It's not really an issue. The average person would have to eat a couple of hundred space elevators before they'd get cancer.

[E-Sabbath]

I rather favor the Space Fountain concept, anyhow. Probably safer in the long run.
http://en.wikipedia.org/wiki/Space_fountain

[Voyager]

.
Of course, the lowest actual price yet recorded is $25 per gram. Using this as our cost for the cable (not of actually building the cable, just collecting the stuff we're going to build it out of) we have a cost of around $19B for the cable. The rest of the numbers also appear to be just stuff he pulled out of the sky.

The cost today is totally irrelevant. Clearly lots of work has to be done on the material, and on manufacturing. We can expect some significant economies of scale, to put it mildly. Who uses this now? If it is made in a lab, $25 a gram is pretty cheap. But saying this is a limiting factor is like saying the Web is impossible because of the cost of mainframe computers in 1964.

[Voyager]

It's because the orbit it's in isn't stable.

You also might have to move it to keep things from crashing into it. Not far, but the possibility exists.

[Voyager]

One thing to remember about a space elevator is you do not need the entire mass of the cable up at once. Remember to build a suspension bridge.. Shoot a small cable over to the other side, then pull the rest of the cable across.. Now, likely it would be impossible to pull the cable up with a smaller one, but construction materials could be pulled up.

So you don't need to get a lot of the millions of kg of material into space right off the bat using normal, innefficient rockets.

True, but you'd have to get the construction infrastructure up there. Look how much the space station has cost. The base for this operation is going to cost a lot more, be bigger, and include a lot more people.

[levdrakon]

How hard would it be to destroy this thing? Could a single madman/terrorist bring the whole thing down with a small plane? Or would the strength of the cable be sufficient to withstand that kind of impact?Probably wouldn't be hard, but from what I've read it would be built out in the ocean, along the equator away from hurricanes and normal aircraft flight paths. It'd probably require some security but hey, we've got a Coast Guard and Air Force, among other things.

[Tenebras]

The cost today is totally irrelevant. Clearly lots of work has to be done on the material, and on manufacturing. We can expect some significant economies of scale, to put it mildly. Who uses this now? If it is made in a lab, $25 a gram is pretty cheap. But saying this is a limiting factor is like saying the Web is impossible because of the cost of mainframe computers in 1964.

The cost today does matter if you're claiming, as Edwards is, that this is a project which can and should be undertaken within the next few years. Also, he doesn't appear to explain where any of his figures come from. What is his justification for a cable mass of 750,000 kg? If you build the cable without a counterweight it works out to, best case scenario, 13,000,000 kg (w/ a density of 1.3 g/cm3). Cutting this cable in half an attaching a whopping big counterweight, you get 7.5 million kg, which is only an order of magnitude off of Edwards' number. Of course, where did his figures come from? Who knows.

By the way, I'm getting my numbers from here (http://www.zadar.net/space-elevator/). The original language was croation, but he at least has the right equations. I haven't checked them all myself, but the things he says are reasonable. By contrast, Edwards just makes grandiose proclamations about powering the thing using space lasers beaming power back and forth. :rolleyes:

[Gangster Octopus]

As to part of the OPs questio, No there are no funds in the stimulus bil directly for a space elevator. In fact there are no funds for any specific projects at all. However, there are research funds for various broader categories that potentially a space elevator could compete for and get on its merits.

[treis]

Outside of it being really cool, what exactly is the point of a space elevator? Do we really need to put that much stuff in orbit (and is there even room) to justify the massive cost of a space elevator when we have a proven technology already capable of the same task.

[billfish678]

Outside of it being really cool, what exactly is the point of a space elevator? Do we really need to put that much stuff in orbit (and is there even room) to justify the massive cost of a space elevator when we have a proven technology already capable of the same task.


Well, yes and no.

We could take the whatever billion we spend each year putting a few people into orbit and few really light probes to other planets and instead put many more people into orbit, go to the moon, asteroids, mars, and send some hefty and much more capable probes to other planets.

REALLY big telescopes in orbit would probably be the most "concrete" benefit.

If you can get the cost per pound WAY down from how we do it now, solar power in orbit might be possible.

[Sitnam]

I get that a geosynchronous satellite can have a line down to earth that doesn't move relative to us, however, sending anything up this line would require it to pull the rope thereby reducing this satellites orbit and bringing the whole ball of wax down to Earth.

Even with counterweights or whatever you are still ultimately pulling the satellite down.

Gravity itself acts on the rope in our atmosphere, the satellites orbit would degrade if we never even used it.

[Chronos]

I get that a geosynchronous satellite can have a line down to earth that doesn't move relative to us, however, sending anything up this line would require it to pull the rope thereby reducing this satellites orbit and bringing the whole ball of wax down to Earth.

Even with counterweights or whatever you are still ultimately pulling the satellite down.

Gravity itself acts on the rope in our atmosphere, the satellites orbit would degrade if we never even used it.This is why the top has to be somewhere above geosynchronous height. The bottom part of the cable is trying to fall down, but the top part is trying to "fall" up, and balances it out (actually, more than balances: You'd want some margin of tension at the Earth anchor point).

As for the benefits of this thing, rockets are (barely) adequate for the sorts of things we use space for right now. But if we could bring down the cost of getting things into orbit by many orders of magnitude, it would open many more applications which aren't even considered right now. You'd start to see things like asteroid mining, or zero-g manufacturing, or space tourism, or low-gravity geriatric homes, or many other possibilities science-fiction authors could tell you about.

[treis]

I get that a geosynchronous satellite can have a line down to earth that doesn't move relative to us, however, sending anything up this line would require it to pull the rope thereby reducing this satellites orbit and bringing the whole ball of wax down to Earth.

Even with counterweights or whatever you are still ultimately pulling the satellite down.

Gravity itself acts on the rope in our atmosphere, the satellites orbit would degrade if we never even used it.

Altitude is determined by the speed of the satellite (I'm simplifying here, don't pick nits). Basically, the faster something is going, the higher it wants to orbit. The counterweight would be held by the elevator in a lower orbit than it "wants" to based on its speed. This causes tension to be formed in the cable, and so long as the weight of the cargo going up the elevator is less than this tension, the counterweight won't be pulled down. Even if it were, it doesn't matter, because orbit altitude is based on speed. Once the cargo got to the top, the counterweight would return to its original orbit. The only way the counterweight would come closer to earth is if its speed were reduced.

[RickJay]

The cost estimates I've seen are in the vicinity of 50 billion dollars. A government could easily afford that.
Fifty billion is a preposterously low estimate. (The $10 billion claimed by Brad Edwards is plainly dishonest.) I would guess that if we started now, a space elevator would cost, at an absolute minimum, one trillion dollars, and that's if everything goes well.

Nobody's even yet inented a practical way of making things go up the elevator.

[levdrakon]

According to this, (http://www.timesonline.co.uk/tol/news/uk/science/article4799369.ece) we've increased the strength of this nano fiber 100 times over the last five years, and it needs to get about 180 times stronger than that, but it seems steady progress is being made in that direction.

The Japanese think they can do it for a trillion yen (£5 billion). I don't believe that, but they are taking it seriously.

It's the little matter of the counter-weight that people seem pretty optimistic about. Oh, just hook an asteroid to one end.

Uh, where are we planning on getting one?

[Chronos]

I would guess that if we started now, a space elevator would cost, at an absolute minimum, one trillion dollars, and that's if everything goes well.Quite possibly, if we started now. That's why we wait for other applications to drive the price of nanofiber down first, before we start on anything elevator-specific. That stuff has impressive enough properties that there will be demand for it, and there's nothing that makes it inherently expensive.

[Bruce Wayne]

Plummeting straight down isn't the issue. It's what happens if it starts wrapping that becomes a problem.

That could be cool. Just think, North America vs. Europe in a giant game of tug-o-war.:)

[billfish678]

Plummeting straight down isn't the issue. It's what happens if it starts wrapping that becomes a problem.

Its most likely gonna burn up in the atmosphere, whether it falls straight down or goes flying sideways as it comes down.

[The Tao's Revenge]

According to this, (http://www.timesonline.co.uk/tol/news/uk/science/article4799369.ece) we've increased the strength of this nano fiber 100 times over the last five years, and it needs to get about 180 times stronger than that, but it seems steady progress is being made in that direction.

The Japanese think they can do it for a trillion yen (£5 billion). I don't believe that, but they are taking it seriously.

It's the little matter of the counter-weight that people seem pretty optimistic about. Oh, just hook an asteroid to one end.

Uh, where are we planning on getting one?

Why not just manufacture a counter weight?

Start with a small cable with a small counter weight and send up more mass to be a counterweight. Then thicker cable then more mass. I don't get the orbit dynamics either though.

If you're pulling your way up the cable than you have to be pulling down on the cable and you can't get blood out of a turnup. The energy has to come out of the counter weight.

[billfish678]

If you're pulling your way up the cable than you have to be pulling down on the cable and you can't get blood out of a turnup. The energy has to come out of the counter weight.

Not quite IF I understand/remember this thing right.

It takes energy to climb the cable, but much? more is supplied by the cable system.

IIRC this "free" energy is supplied by the earths rotation being slowed down by an itsy bitsy bit.

Its late, I'm tired and this could all be BS though...

[RickJay]

Quite possibly, if we started now. That's why we wait for other applications to drive the price of nanofiber down first, before we start on anything elevator-specific. That stuff has impressive enough properties that there will be demand for it, and there's nothing that makes it inherently expensive.
I'd say the carbon nanofiber will be the least of your expense concerns.

Explain to me how they plan to string it up fifty thousand miles. That task alone promises either disastrous or comical misadventure on a truly global scale; I can see the CNN footage now, "Yet Another Space Elevator Cable Floating In Pacific." How're they planning to rocket a space station that big into that high an orbit? How are they going to power the elevator - again, something nobody's ever satisfactorily explained beyond "uh, like, we'll invent a laser thing"? What amazingly strong edifice is going to hold the tether down?

A space elevator would not just be the biggest engineering project ever undertaken, it would be the biggest by at least two orders of magnitude. It's a project of staggering complexity, construction effort, and orbital launch effort, and requires the invention of many things that do not yet exist. So as per the OP. it's a pretty bad choice for a fiscal stimulus idea.

[Chronos]

So as per the OP. it's a pretty bad choice for a fiscal stimulus idea. Oh, I never disputed that. It might be a good choice to stimulate the economy out of the Recession of 2063, but it definitely won't be shovel-ready in time for this one right now.

[Lumpy]

I'd say the carbon nanofiber will be the least of your expense concerns.

Explain to me how they plan to string it up fifty thousand miles. That task alone promises either disastrous or comical misadventure on a truly global scale; I can see the CNN footage now, "Yet Another Space Elevator Cable Floating In Pacific." How're they planning to rocket a space station that big into that high an orbit? How are they going to power the elevator - again, something nobody's ever satisfactorily explained beyond "uh, like, we'll invent a laser thing"? What amazingly strong edifice is going to hold the tether down?

A space elevator would not just be the biggest engineering project ever undertaken, it would be the biggest by at least two orders of magnitude. It's a project of staggering complexity, construction effort, and orbital launch effort, and requires the invention of many things that do not yet exist. So as per the OP. it's a pretty bad choice for a fiscal stimulus idea.Why are we still debating the practicality of building a ginormous space elevator? It doesn't have to be huge. It has to be very long, yes. But it doesn't have to be thick or wide. The first one can be 40,000 kilometers long, 5 cm wide, and 10 microns thick. The starting weight at geosynch could be less than what we're currently planning to boost to translunar trajectory. If the first version can only lift a metric ton at a time, that's still good enough to get servicable satellites into geosynchonous orbit, and then it can start lifting it's successor.

[Tenebras]

If it's only 40,000km long, then you have to attach a gigantic counterweight to the end floating out there in space, and that makes deployment that much more difficult. Also, the materials to build the 40,000km ribbon... wait for it... don't exist. And even if they did exist, the cable is a design nightmare. It's tens of thousands of miles long and every single point along all that length is a point of critical failure. The entire mechanism is a single point of failure. And if it fails, it fails catastrophically. Best case scenario, the whole thing just floats off into space and is never seen or heard from again. Slightly less best case scenario, it burns up in the atmosphere before it gets the chance to kill anyone directly or give them cancer.

As for being thick and wide, if you try to build one out of any material actually known to man, it does have to be thick and wide, as well as long. That's because your cable diameter grows exponentially as you approach the top, in order to support the cable hanging below. So unless you make it out of concentrated magic, it's going to be both thick and long. So step one is to invent the strongest and lightest material ever, and then follow up by producing gigantic quantities of it, which you ship into space. Once you get it to space, you park it in an unstable orbit and just hope and pray that the stuff you built it out of is resistant to pretty much every form of radiation in the universe, as well as the thermal effects of cycling from daylight to darkness in a 24 hour cycle.

If you completely ignore all of the practical problems of building it, it just barely works in the idealized world of a single planet, with no atmosphere, and no other bodies in the universe. Truly, the space elevator concept is like storing your sharpened pencils balanced on their tips on your desk. They'll never fall down because if you set them down just right, they will be in equilibrium and there is no power in the universe strong enough to upset that.

Arguing about building space elevators is a bit like arguing about building trans-Atlantic tunnels. Sure, it would be awesome to ship BMWs from Germany to the United States via automated underwater supertrains, but it's not going to happen in your lifetime, or anyone else's, because the project is just not feasible. Even if somebody with a Ph.D. made a poorly written report to a NASA subsidiary and has an equally poorly written book available for purchase on Amazon.

[Lumpy]

Tenebras, I think you're way overstating the problems that need to be solved.

First of all, if space elevators were truly inherently unstable, somone would have produced a paper decades ago pointing this out (the way fans quickly calculated that Niven's hypothetical Ringworld was unstable), and no one would even be discussing the concept today. Any tendency for the tether to either drift away or collapse to Earth is solved by the simple expediency of anchoring it to the ground and giving it a net tension away from Earth greater than any perturbation that would move it towards Earth.

Second, you're still thinking that the tether must require millions or billions of tons of mass, if it's to be made of "any material actually known to man". We have a material known to man that is strong enough: carbon nanotubules. The only question is whether we can actually produce a real-world cable within an order of magnitude of the theoretical maximum strength that carbon nanotubules can possess. For strength ratios considered achievable, the "exponential" increase in thickness might be 50 to 1. So Space Elevator 1.0 would be a ribbon 10 microns thick at the ground and half a millimeter thick at the top. Weight to be initially boosted to geosynch orbit is on the order of hundreds of tons, not millions. We can't do this today, we can't do this next year, we probably can't do it in five years. But it's not wild-eyed fantasy to suppose we might be able to do it in twenty years.

Third, the single-point failure argument can be solved by simple redundancy, like any load-bearing application of cable or rope today. You have a 2-3X safety factor built in, and you use multiple strands so that the failure of any one doesn't singlehandedly snap your cable. Protecting the cable against various sources of degradation is a serious concern, but again probably not an insurmountable one.

[billfish678]

[
Third, the single-point failure argument can be solved by simple redundancy, like any load-bearing application of cable or rope today. You have a 2-3X safety factor built in, and you use multiple strands so that the failure of any one doesn't singlehandedly snap your cable. Protecting the cable against various sources of degradation is a serious concern, but again probably not an insurmountable one.


Anybody know how often that cable is going to be hit by orbiting debris?

Gut feeling tells me its is more than a year but not so long a time frame it won't even be a worry either.

[Tenebras]

Tenebras, I think you're way overstating the problems that need to be solved.


I obviously don't think I'm overstating them. I actually thought I was being optimistic by admitting it would be possible if you could distill magic. ;)


First of all, if space elevators were truly inherently unstable, somone would have produced a paper decades ago pointing this out (the way fans quickly calculated that Niven's hypothetical Ringworld was unstable), and no one would even be discussing the concept today. Any tendency for the tether to either drift away or collapse to Earth is solved by the simple expediency of anchoring it to the ground and giving it a net tension away from Earth greater than any perturbation that would move it towards Earth.


A space elevator is, fundamentally, a geosynchronous satellite. It's kind of a tricky geosynchronous satellite in that it has a feeler which reaches down to the surface of the Earth, but that doesn't really change anything. That's what makes the idea neat in the first place.

(If you want to make your life as simple as possible, you put it into a geostationary orbit, otherwise you have an even trickier engineering problem to solve, what with the bending and whatnot.)

Now, nobody needs to publish a paper to show that this orbit is unstable, because it's already known. It's not even particularly difficult to show, and neither is it a great mystery. Wikipedia (http://en.wikipedia.org/wiki/Geostationary_orbit) knows it. Here's a derivation (http://newton.ex.ac.uk/research/qsystems/people/sque/physics/geostationary-orbit/). The reason the orbit is unstable is the same reason that any orbit is unstable, because small perturbations from other bodies such as the moon or the sun increase or decrease the speed of the satellite, which necessarily change its orbit. Normally this isn't such a big deal, and you just put a small thruster on the satellite to push it back into place. When it runs out of fuel, you put up another satellite. If it drifts a tiny bit, no worries, it's not like your communications satellite is a 50,000 mile string attached to the ground or anything.

As for attaching this thing to the ground, what exactly is the plan to do this? All of the space elevator people say "Oh, we'll just attach it to the ground!" and pretend that's the end of the story. Attach it where and with what? If you attach it out in the ocean you're talking about a permanent sea base in the middle of the pacific, which I think is a much more likely project to be completed in our lifetimes. (slim chance being somewhat more hopeful than fat chance) If you attach it to the ground somehow, then you can't very well move it around if you see an asteroid coming, now can you? More on this point later.


Second, you're still thinking that the tether must require millions or billions of tons of mass, if it's to be made of "any material actually known to man". We have a material known to man that is strong enough: carbon nanotubules. The only question is whether we can actually produce a real-world cable within an order of magnitude of the theoretical maximum strength that carbon nanotubules can possess. For strength ratios considered achievable, the "exponential" increase in thickness might be 50 to 1. So Space Elevator 1.0 would be a ribbon 10 microns thick at the ground and half a millimeter thick at the top. Weight to be initially boosted to geosynch orbit is on the order of hundreds of tons, not millions. We can't do this today, we can't do this next year, we probably can't do it in five years. But it's not wild-eyed fantasy to suppose we might be able to do it in twenty years.


Look, here's an incredibly optimistic paper (http://www.liftport.com/papers/2005Nov_LP-Ribbon_Mass.pdf) (pdf) written by a guy who works for a Space Elevator Booster corporation. (Get it, booster?) Check out Figure 2. CNTs have a density of between 1.3 and 1.4 g/cm3, which puts us between the yellow and the green curves. (If we build it out of water, we can use the red curve.) According to wikipedia, in 2000, somebody built a nanotube that measured a tensile strength of 63 GPa. This seems to be a reference to this paper (http://www.sciencemag.org/cgi/content/abstract/287/5453/637). (abstract only) You'll note that the tubes ranged in tensile strength from 11 to 63 GPa, although 63 GPa is the figure which seems to be cited as the "tensile strength of CNTs". You will also notice that this was not a test on a macroscopic scale. The entire testing apparatus fit into the imaging chamber of a scanning electron microscope. (That is, it 'tweren't very big.)

Back to the point, referencing figure 2 of the incredible optimistic paper, we see that if we have a tensile strength of 50 GPa we're talking about a mass of between 400 and 700 metric tons. (I'm estimating the green curve, obviously, but it looks to be a bit larger than 1.5 times the yellow curve, and both curves ought to be exponential.) That's if the cable can uniformly withstand 50 GPa and we accept a factor of safety of 1. If the cable is weaker, the situation only gets worse, of course. (Remember, this is the graph which gives bare minimum masses supplied by the true believers who think the whole thing can be put into operation for only $1B.)

For comparison, the mass of the ISS in October 2008 was 227 metric tons. (wikipedia (http://en.wikipedia.org/wiki/International_Space_Station) or the NASA fact sheet (http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf) (pdf) the wikipedia number came from)


Third, the single-point failure argument can be solved by simple redundancy, like any load-bearing application of cable or rope today. You have a 2-3X safety factor built in, and you use multiple strands so that the failure of any one doesn't singlehandedly snap your cable. Protecting the cable against various sources of degradation is a serious concern, but again probably not an insurmountable one.

If you put two of them next to each other and one of them snaps, I'll wager my dollars against your nickels that the broken one takes out the whole one. That's rather the problem with a cable several tens of thousands of miles long under truly ridiculous tension.

Now, about moving it around to avoid collision, and other fantasies. In the first place, it's an incredibly long ribbon trailing off the Earth. You have a snowball's chance in hell of moving it in an equatorial direction if you're very careful and your god smiles upon you, but you can't move it longitudinally because, well, because it's a big ribbon trailing off the surface of the Earth. Even if you don't have it based on the equator, once you get a couple thousand miles up, you might as well be. Of course, trying to move it is just going to set the thing waggling, at which point it rips itself to pieces. Congratulations.

Speaking of which, suppose that we build this wild and crazy thrill ride in the sky. Every country on Earth has its own little sector of geostationary orbit mapped out for it. If any one of those countries puts a satellite in orbit whose orbit then decays (after, for instance, the satellite runs out of fuel) it's going to go straight through your cable. For that matter, there are very few orbits (read none) which don't cross the equator. So every single piece of detritus in orbit around the Earth is potentially going to hit your cable. Since nothing is in geostationary orbit for long (on account of that pesky moon of ours, for example), all of that stuff is going to be swirling around our precious space elevator.

I saw one of the people writing about this idea said that it would be safe from terrorist attacks because you could build it in the middle of the pacific, and then just not let anybody within a thousand miles of that patch of the Pacific. Pretty theory, but completely worthless when you consider that Iran just popped a satellite into orbit, and the Chinese and the Russians have been doing it for years. If they really wanted to piss us off, they'd just lob a fragmentation grenade into orbit and then watch the pretty light show as the elevator collapsed. Or, blow up a satellite (http://www.washingtonpost.com/wp-dyn/content/article/2007/01/18/AR2007011801029.html) in orbit and make a big ass (technical term) debris cloud.

[Tenebras]

Anybody know how often that cable is going to be hit by orbiting debris?

Gut feeling tells me its is more than a year but not so long a time frame it won't even be a worry either.

Depends on what you mean by orbiting debris. Something big? Doesn't happen that often, but it definitely occurs. Little stuff? All the time. NASA FAQ (http://orbitaldebris.jsc.nasa.gov/faqs.html) on orbital debris. Here's another page talking about it. Geeky blog (astroprofs) (http://astroprofspage.com/archives/256) NASA sent a satellite into low Earth orbit and then recovered it. In just under 6 years they recorded 20,000 impacts. NASA page on orbital debris (http://www.orbitaldebris.jsc.nasa.gov/protect/impacts.html).

Funny story, they sent the "let's get smacked with debris" satellite up and intended for it to orbit for around a year, but then Challenger happened and they couldn't get it back until almost 6 years had elapsed. Ok, not funny-ha-ha funny, but I still like it.

[billfish678]

For comparison, the mass of the ISS in October 2008 was 227 metric tons. (wikipedia (http://en.wikipedia.org/wiki/International_Space_Station) or the NASA fact sheet (http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf) (pdf) the wikipedia number came from)

.

Well, to be fair, using the Shuttle to place mass into orbit aint optimum at all.

Though , no matter what current or near current rocket system you use to get all that mass up there is going to be pretty darn expensive.


Not that most of the rest of your post doesnt have good points....

[Chronos]

Now, nobody needs to publish a paper to show that this orbit is unstable, because it's already known. It's not even particularly difficult to show, and neither is it a great mystery. Wikipedia knows it. Here's a derivation. The reason the orbit is unstable is the same reason that any orbit is unstable, because small perturbations from other bodies such as the moon or the sun increase or decrease the speed of the satellite, which necessarily change its orbitI don't think that "unstable" means what you think it means. Most orbits are not unstable, unless you're talking about things like gravitational radiation which would take longer than the lifetime of the Universe to bring a satellite down. Unstable does not mean that there are perturbations on the orbit; there's perturbations on everything. The question of stability is how a system responds to those perturbations. If a system is unstable, then the perturbations will grow exponentially; if it's stable, then the perturbations will be damped out or reversed. Geosynchronous orbits are stable, which means that the effects of the perturbations will not be significantly larger than the perturbations themselves, which is to say small. A space elevator is even more stable than a standard geosynchronous orbit, since it's further stabilized by being anchored to the Earth at the bottom.

[Tenebras]

I don't think that "unstable" means what you think it means. Most orbits are not unstable, unless you're talking about things like gravitational radiation which would take longer than the lifetime of the Universe to bring a satellite down. Unstable does not mean that there are perturbations on the orbit; there's perturbations on everything. The question of stability is how a system responds to those perturbations. If a system is unstable, then the perturbations will grow exponentially; if it's stable, then the perturbations will be damped out or reversed. Geosynchronous orbits are stable, which means that the effects of the perturbations will not be significantly larger than the perturbations themselves, which is to say small. A space elevator is even more stable than a standard geosynchronous orbit, since it's further stabilized by being anchored to the Earth at the bottom.

Yeah, that's what I meant.* The problem with geosyncronous orbits is that once perturbed, they are no longer geosynchronous. Not a big deal if you're a free floating satellite because if you get a bit off from where you're supposed to be, you fire up the main thrusters and you cruise on back to where you oughta be. (more or less) If you anchor the elevator to the ground and then it starts drifting, you're going to have serious problems, because the ground isn't drifting, too. Even the people who think the space elevator is possible recognize that you have to be very careful about maintaining the orbit, they just handwave away the difficulty of moving a ginormous diamond ribbon back where you want it to be.

* I'm actually teaching Differential Equations this semester. I know that internet appeals to authority are not worth the paper they're printed on, but I feel like it's worth pointing out. I started reading about this stuff because I thought it might be a fun project for my students to work out the details of how a space elevator would work. Unfortunately, most of the equations don't have elementary solutions, so I think it's a project better suited to a numerical methods class. I'm still planning to use this as an "interesting real world example" though.

[billfish678]

Unfortunately, most of the equations don't have elementary solutions, so I think it's a project better suited to a numerical methods class. I'm still planning to use this as an "interesting real world example" though. [/SIZE]

Given your recent posts I just love irony of that part.

You work in academia dont you ?:)

[Tenebras]

Also, because the Earth is flattened in the polar direction, if the inclination of an orbit is not exactly 0, it will drift. Then there's also the issue of the ellipticity of the equator and... yeah. Not going to get into it. But the upshot is, you can't just hang a ribbon off the actual Earth and expect it to stay put without giving it little pushes.

[Tenebras]

Given your recent posts I just love irony of that part.

For certain values of real world.

You work in academia dont you ?:)

Does it show?

[Sage Rat]

To add some economic talk to this discussion, I'll just note that a space elevator or space fountain would likely be a poor means of stimulus.

1) It could spend a decade just in planning. Economic stimuli are things that effect the economy now, not ten years from now.

2) A "good" economy is one in which there is growth. The way you create growth is by figuring out some project that, if completed, will earn more money than it cost to make within a short enough period of time to be worthwhile (i.e. before you go bankrupt.) Some infrastructure programs can help to improve trade and so, even though there is no toll to use the infrastructure, the money spent on the infrastructure is made back via the increase in trade. A space elevator, though, is essentially the world's biggest Bridge to Nowhere. Getting into space is entirely about coolness until such a time as we have the speed capabilities to take advantage of the resources and land available in space. So essentially it would just be a big money sink on the economy, not a boon. The only way it would help the economy would be via the creation of the materials used. But you could build a bridge connecting Europe and North America instead of a space elevator and get those same materials, plus something useful.

[mswas]

We already have a material which is plenty light and strong enough to build rockets out of... It's called aluminum. The weight of the hull of any rocket is negligible compared to the weight of the fuel-- That's the reason it costs so much to launch anything into orbit on a rocket. A space elevator bypasses that requirement.

The cost estimates I've seen are in the vicinity of 50 billion dollars. A government could easily afford that.

Oh, and as for the "what if it breaks" argument, in that case it would burn up in the atmosphere before hitting anything on the ground. We'd be out our initial investment, of course, but it wouldn't be a cataclysmic global apocalypse.

Umm the top part would, not all of it would burn up on re-entry.

[wevets]

So is it safe to assume the Kim Stanley Robinson scenarios in his Mars books have no basis in reality? How much of the space elevator would survive re-entry?

[billfish678]

Umm the top part would, not all of it would burn up on re-entry.

Anything more than about 50-100 miles up would most likely burn up. That much of the cable would weigh something in the tons range.

A falling plane is just as dangerous, if not more so.

[Chronos]

But the upshot is, you can't just hang a ribbon off the actual Earth and expect it to stay put without giving it little pushes. ...Or little pulls. Which is really easy, given that it's a cable and that it's anchored to a point on the Earth.

[Diz]

So is it safe to assume the Kim Stanley Robinson scenarios in his Mars books have no basis in reality? How much of the space elevator would survive re-entry?

I have no idea if his idea is realistic or not, but in his favor is the fact that Mars has significantly less atmosphere for the cable to burn up in. I also seem to remember the cable in his story being quite a bit larger than anything proposed in this thread.

[E-Sabbath]

Once again, the 'space fountain' manages to ignore pretty much _all_ of these issues. It just requires a bit more power. Nice trick, huh?

[Tenebras]

...Or little pulls. Which is really easy, given that it's a cable and that it's anchored to a point on the Earth.

What, exactly, do you envision when you say "anchored"? What kind of tension are we talking about at the bottom of the cable? Will this be on land or at sea? How do you imagine the "little pulls" might be accomplished?

[Tenebras]

Once again, the 'space fountain' manages to ignore pretty much _all_ of these issues. It just requires a bit more power. Nice trick, huh?

A "space fountain" is a railgun you can never turn off, firing constantly at a station in the sky, which shoots them back down at you. It has all of the practicality of a space elevator with the extra added bonus of being a superweapon. Oh, and if you ever do need to turn it off, it falls down.

Just checked wikipedia to refresh my memory on the idea and... you need to build an airtight tower 100km tall? For reference, the tallest structure ever built, when they finish it, will be the Burj Dubai tower which has a TV antenna that's 818m high. Make that airtight and you're 0.8% of the way there!

[scr4]

Anything more than about 50-100 miles up would most likely burn up. That much of the cable would weigh something in the tons range.
Why would it burn up? It's not moving at orbital speed, so the cable has very little kinetic energy when it hits the atmosphere. Only what it acquires during the fall.

[billfish678]

Why would it burn up? It's not moving at orbital speed, so the cable has very little kinetic energy when it hits the atmosphere. Only what it acquires during the fall.

you fall 50 miles and see how much kinetic energy YOU have :)

Burt Rutan's Space Ship One "only" went up and down about 50 miles and reentry heat wasnt something they could just shrugg off. It certainly did not have anywhere near orbital velocity.

Hence, my 50 to 100 mile WAG.

[SteveG1]

There isn't enough money in the world to build a space elevator, and half the technology to construct and operate it isn't worked out yet.

Since there's really no chance at all that such a thing could be constructed in our lifetimes - sorry, Chronos, it is not going to happen - you would probably get much more effective stimulus by simply dropping bales of money out of helicopters flying over low-income neighborhoods.

Agree. the whole idea is unsound. We don't have the money, the materials, the technology. If we did, we still have to buck up against laws of physics dealing with orbital speeds vs earth rotational speed, altitude, tension, gravity, voltage build up on the cable (the voltages will be gigantic), etc etc etc. Let's go with better "conventional" launch systems instead.

[Chronos]

Agree. the whole idea is unsound. We don't have the money, the materials, the technology. If we did, we still have to buck up against laws of physics dealing with orbital speeds vs earth rotational speed, altitude, tension, gravity, voltage build up on the cable (the voltages will be gigantic), etc etc etc. Let's go with better "conventional" launch systems instead.The technology we don't have is the materials, and the lack of money is just because we don't have the materials yet. So that's really only one objection, which I've already explained why I think it will be resolved in the not-too-distant future. And there is nothing in the laws of physics which presents an obstacle: The physics all works out just fine, provided you have the material available.

[E-Sabbath]

Tenebras, one of the nice things about the fountain is that the things being shot up it help keep it up.
... it's still easier to build than the elevator.

Another variant I like that I forget the name of is the pinwheel. Central body in space, rotating arms, no attachment to the earth. You board as it passes.

[Tenebras]

Tenebras, one of the nice things about the fountain is that the things being shot up it help keep it up.
... it's still easier to build than the elevator.

Another variant I like that I forget the name of is the pinwheel. Central body in space, rotating arms, no attachment to the earth. You board as it passes.

The things being shot up are the only thing keeping the station up. The space fountain is a continuously running railgun launcher. So the first thing you have to do is build a railgun launcher that works one time, and then just hold down the trigger. Again, the people who think it will work admit that one part of the process is to build a tower 100 times taller than any structure on Earth, and then pump all the air out.

It's just not going to happen.

[Tenebras]

The technology we don't have is the materials, and the lack of money is just because we don't have the materials yet. So that's really only one objection, which I've already explained why I think it will be resolved in the not-too-distant future. And there is nothing in the laws of physics which presents an obstacle: The physics all works out just fine, provided you have the material available.

Even if you discovered a scrith mine, it still wouldn't happen. Even if you get an army of wizards to cast Wish spells until the thing is in place, and then a second army of clerics all cast Miracle to hold it there, it gets hit with a piece of garbage and goes kaplooie.

And the physics don't work out fine. Try this: ignore the moon, sun and every other body in the universe. Assume that the Earth is an ellipsoid, flattened through the poles. What orbit are you going to put this in, and how are you going to keep it there?

[Lumpy]

And the physics don't work out fine. Try this: ignore the moon, sun and every other body in the universe. Assume that the Earth is an ellipsoid, flattened through the poles. What orbit are you going to put this in, and how are you going to keep it there?I don't understand why you're assuming that any perturbation on the tower will be self-accellerating. It's NOT a "pencil balanced on it's point" situation. As far as I can tell, the effects of the moon, sun and an imperfectly spherical Earth will simply mean that the top end will wobble about a bit.

[billfish678]

Tenebras, one of the nice things about the fountain is that the things being shot up it help keep it up.
... it's still easier to build than the elevator.

Another variant I like that I forget the name of is the pinwheel. Central body in space, rotating arms, no attachment to the earth. You board as it passes.

Thats the one I keep remembering.

Hundreds of miles of cable rather than 10s of thousands.

[Dilton Doiley,Philosopher King]

Agree. the whole idea is unsound. We don't have the money, the materials, the technology.

We have the manpower though, and that manpower can help make the money, materials and technology happen. 12.5 million people are unemployed in the US. Creating a space elevator would create jobs and a new paradigm of research and technological advances.

[gaffa]

The interesting thing about nanotubes is that they are produced by the ridiculously simple technology of a candle flame and are found in soot. The expensive part is filtering out all the other stuff from the soot. I think we'll see a breakthrough in the next few years with a system able to produce nanotube filaments of unlimited length from a pyrotechnic source.

If we had this, a system that could produce industrial quantities of filament to order, on location...how difficult is the rest?

As for the value of it, the most worthwhile project would be unlimited power from solar panels in space. Make the mass of the counterweight was a huge farm of solar panels. Constant access to the sun and ship the power down the filament. The crawler would have to be a Faraday cage, so no leaning out the window.

[runcible spoon]

Hey, while we're stimulating the economy, can I have a gravity train? (http://en.wikipedia.org/wiki/Gravity_train)

[Tenebras]

I don't understand why you're assuming that any perturbation on the tower will be self-accellerating. It's NOT a "pencil balanced on it's point" situation. As far as I can tell, the effects of the moon, sun and an imperfectly spherical Earth will simply mean that the top end will wobble about a bit.

Because it's not a situation where the thing just wobbles a bit.

Here (http://www.absoluteastronomy.com/topics/Orbital_stationkeeping) is a brief discussion of some of station keeping operations for satellites in GEO and GSO. Also, the ground tracks for satellites are "small wobbles" but they still cover a heck of a lot of ground. Pretty picture (http://celestrak.com/columns/v04n07/) of ground tracks.

[Tenebras]

Hey, while we're stimulating the economy, can I have a gravity train? (http://en.wikipedia.org/wiki/Gravity_train)

The only obstacle is inventing the materials that can withstand the heat and pressure of the Earth's mantle and core!

[RaftPeople]

Ok, be kind if completely wrong, but it seems that something on this scale might have some interesting side effects. Would any kind of electric current be induced in this elevator (if anchored? or maybe even if not)? Carbon nano-tubes can be semi-conductors, and even though it's moving with the earth's magnetic field, not sure if there are other fields surrrounding the earth that could cause it, interaction with particles from the sun, etc.. Or maybe static electricity build up on it?

[runcible spoon]

The only obstacle is inventing the materials that can withstand the heat and pressure of the Earth's mantle and core!

Hey, if they can do it in The Core...


Actually, despite the amazingly rendered animation on the wiki page, you don't have to go through the core. You can also do diagonals. Of course, even at a diagonal we're talking several miles down, and you really ought to create a vacuum for best efficiency, but at least it won't fall on you when it fails...

[Diz]

Because it's not a situation where the thing just wobbles a bit.

Here (http://www.absoluteastronomy.com/topics/Orbital_stationkeeping) is a brief discussion of some of station keeping operations for satellites in GEO and GSO. Also, the ground tracks for satellites are "small wobbles" but they still cover a heck of a lot of ground. Pretty picture (http://celestrak.com/columns/v04n07/) of ground tracks.

It's entirely possible I'm missing something important, but I don't see the problem here. If you have a space elevator, getting fuel to GEO for station keeping shouldn't be much of a concern. And I don't see why the ground tracks are significant. Is there any reason why the anchor point has to precisely align with the ground track? We're talking about cables, not rigid towers. A bit of swaying at the top shouldn't matter, at least compared to the kinds of forces you'll already be dealing with.

Not that I expect a space elevator to be built anytime soon, but as I understand it, the primary challenges are engineering and materials problems, not fundamental flaws in the physics of the concept.

[Chronos]

Another variant I like that I forget the name of is the pinwheel. Central body in space, rotating arms, no attachment to the earth. You board as it passes.I think this would only work in vacuum-- Air resistance would be prohibitive on Earth. But it'd be a good complement to the Space Elevator for slowly-rotating, airless worlds like Luna or Mercury. Between elevators on Earth, Mars, and the gas giant moons, and pinwheel skyhooks on Luna and Mercury, you could go anywhere you want in the system except for Venus, and honestly, who wants to go to Venus anyway?

[billfish678]

I think this would only work in vacuum-- Air resistance would be prohibitive on Earth. But it'd be a good complement to the Space Elevator for slowly-rotating, airless worlds like Luna or Mercury. Between elevators on Earth, Mars, and the gas giant moons, and pinwheel skyhooks on Luna and Mercury, you could go anywhere you want in the system except for Venus, and honestly, who wants to go to Venus anyway?

The way I recall it, the wheel rotates at the VERY top of the atmosphere, space bascially. You "just" jump up 50 to a 100 miles high to catch the ride.

[Sam Stone]

If we could build large quantities of nanotube sheets, I think I'd rather see something like an Orbital Balloon (http://www.msnbc.msn.com/id/5025388/).

First, you build a balloon big enough and light enough that it can climb to 140,000 feet. There, you assemble a much bigger one, which isn't affected by weather and turbulence and which stays up all the time. It's basically a floating waypoint. Then at this one, you build a truly humongous balloon (over a mile long) that is so light it can climb even in the rarified atmosphere above 140,000 ft. You put an ion drive on this one so that as it climbs it very slowly accelerates until it's eventually in orbit. To come down, you just decelerate, and let it float back down slowly through the atmosphere.

It's a pretty cool concept, and it's actually being built right now. The company has had contracts from the military for building the suborbital waypoint station, and has been test-flying its balloons for years. Unfortunately, they recently had one of their big ascender balloons ripped apart in high winds, but they're seriously funded and have large facilities and are continuing work.

Here's a PDF describing the concept in detail (http://www.jpaerospace.com/atohandout.pdf)

Anyone want to poke holes in this idea?

[Locrian]

Well there is the fact that it would be super expensive. Also, have you ever seen what a taut cable does when it suddenly snaps? It uncoils and whips around like an angry snake. Do you really think that is a good idea with a 500 mile long cable?

Bryan: I think the ideas of Buckminster Fuller will be applied at the nano-scale in materials a lot more, and we'll be seeing those materials start to appear within the next twenty years. I expect another major space push by mid-century. People will capitalize on the 100 year anniversaries of everything in order to gain funding for projects.

Yes. "Modern Marvels" on history channel shows a design for a space elevator we could build right now. If the elevator is anchored in say, Ft. Worth, and the cable snaps at the bottom, your house in Idaho could get swiped. (!)

If cable breaks up top, not only will a flaming cable come down but the elevator in space would crash too, giving us a blast as big as an asteroid on the surface.

Can't build it yet.

[Lumpy]

Because it's not a situation where the thing just wobbles a bit.

Here (http://www.absoluteastronomy.com/topics/Orbital_stationkeeping) is a brief discussion of some of station keeping operations for satellites in GEO and GSO. Also, the ground tracks for satellites are "small wobbles" but they still cover a heck of a lot of ground. Pretty picture (http://celestrak.com/columns/v04n07/) of ground tracks.Good points, but wouldn't the fact that the tether is anchored to the ground limit how far the it could deviate from it's orbit? It still seems to me that all perturbative forces would do would add a small amount of extra strain on the tower.

[levdrakon]

Yes. "Modern Marvels" on history channel shows a design for a space elevator we could build right now. If the elevator is anchored in say, Ft. Worth, and the cable snaps at the bottom, your house in Idaho could get swiped. (!)

If cable breaks up top, not only will a flaming cable come down but the elevator in space would crash too, giving us a blast as big as an asteroid on the surface.

Can't build it yet.I live under an airport approach path, and have a couple dozen large jets flying over that could crash into my house every single day of the year. I don't lose sleep, even though it's a fact they sometimes do crash into houses.

What makes you think the elevator would crash like a meteor? We can't put parachutes on the things?

[billfish678]

What makes you think the elevator would crash like a meteor? We can't put parachutes on the things?


You don't even need that really.

The thing is going to be so lightweight per foot of length its going to be more like falling kite string than falling steel girders.

[Locrian]

I live under an airport approach path, and have a couple dozen large jets flying over that could crash into my house every single day of the year. I don't lose sleep, even though it's a fact they sometimes do crash into houses.

What makes you think the elevator would crash like a meteor? We can't put parachutes on the things?

The broken cable would demolish an airport if detached from the ground.
If detached from the top, the ship or platform would slowly enter orbit falling, heating up and BOOOM! Parachutes would flame up too.

Check historychannel.com Great show!

[enipla]

The broken cable would demolish an airport if detached from the ground.
If detached from the top, the ship or platform would slowly enter orbit falling, heating up and BOOOM! Parachutes would flame up too.

Check historychannel.com Great show!ehh?

If detached from the ground, the counter weight or station in space would enter a higher and higher orbit, pulling the cable with it. The idea is that there is tension on the cable.

If detached from the top, the cable would fall (burn up?) and the station would still just float off into space. Unless of course there was the ability to slow it's orbit down.

[levdrakon]

The broken cable would demolish an airport if detached from the ground.
If detached from the top, the ship or platform would slowly enter orbit falling, heating up and BOOOM! Parachutes would flame up too.

Check historychannel.com Great show!Well, I'm confused. I'm talking about what would happen if the crawler fell, and we would certainly build in some safeguards to keep it crashing like an asteroid. It wouldn't really be that big anyway.

If we're talking about the nano-fiber ribbon, I don't see how it's going to hit me with more force than a string of yarn floating down.

[Chronos]

Quoth Sam Stone:If we could build large quantities of nanotube sheets, I think I'd rather see something like an Orbital Balloon.

First, you build a balloon big enough and light enough that it can climb to 140,000 feet. There, you assemble a much bigger one, which isn't affected by weather and turbulence and which stays up all the time. It's basically a floating waypoint. Then at this one, you build a truly humongous balloon (over a mile long) that is so light it can climb even in the rarified atmosphere above 140,000 ft. You put an ion drive on this one so that as it climbs it very slowly accelerates until it's eventually in orbit. To come down, you just decelerate, and let it float back down slowly through the atmosphere.I've been thinking a bit about this, and the biggest objection I can see is that if the balloon is big enough to get non-negligible lift at whatever height it operates at, then it'll also be big enough to get non-negligible drag at that height, too, which would be a big problem at orbital speeds. You could still use the balloon itself as a replacement for satellites for some purposes, and you could potentially use it as a launch platform for semi-conventional rockets which would be freed from the burden of punching through most of the atmosphere.

[Sam Stone]

The balloon doesn't just get static lift - it gets dynamic lift through its own propulsion. Think of it slowly 'skipping' across the top of the atmosphere as it accelerates over a period of 5 days. Because it gets dynamic lift, it goes higher as it goes faster, and needs fewer molecules to keep it 'flying'. The key to it is it's gigantic size coupled with very low weight. You don't need that many molecules to keep it flying.

I think the math on this actually works out. This isn't pie-in-the-sky - these guys are building these balloons today. Did you follow the link to their web site? Their facilities are quite large and impressive.

There are some identified problems. One is actually building the balloon at what they call 'dark sky station', a gigantic floating factory 2 miles across and at 140,000 feet. The problem is that the environment is damned close to outer space, requiring full pressure suits and all that, and yet they're still at full gravity since they're just floating above the earth like a hot air balloon. That's a challenging environment to do construction in.

Another problem is that since the 'ascender' balloon takes 5 days to reach orbit, it's going to be subjected to a lot of radiation. It'll need some serious shielding for the astronauts.

But compared to the difficulty of building a space elevator, this is nothing. Just extensions of known engineering. No exotic unobtanium required - just money and effort. And if you could get the system working well, it would be incredibly cheap to get to orbit - probably as cheap as your space elevator. Nothing is subjected to re-entry heat. Nothing is under any kind of radical acceleration. you just float up your payload or people to the way station, move them into another balloon, and gently fly up into orbit. The risk goes way down as well, and there are no catastrophic failure modes that threaten people on the ground in any large way.

All in all, it's a pretty cool concept, and one I give much more credence to than a space elevator for having a chance to actually be functional within my lifetime.

[Chronos]

And if you could get the system working well, it would be incredibly cheap to get to orbit - probably as cheap as your space elevator.I've no doubt that something like this could lead to costs radically lower than chemical rockets, but you can operate a space elevator at an arbitrarily low energy cost per mass lifted. If this giant balloon can work (and I'd want to work through the math myself), then they can almost certainly get it going sooner than a space elevator, though, and there's no sense putting all of our eggs in one conceptual basket.

[Sage Rat]

Wouldn't shooting a rocket off of a hydrogen balloon generally be referred to as a "bad thing"? ;)

But more seriously, exactly how big would this thing need to be to support the weight of a full rocket?

How much does shooting from a higher point save us in terms of weight?

If you're that far above most of the atmosphere, does that mean that the balloon would be stable enough to support something like this? I would be worried that without much atmosphere, even if there was no wind, that any change in weight on any point on the surface would cause the whole thing to bobble and lean. There just wouldn't be much stabilizing it. I wouldn't want to shoot a rocket off of something where the lightest touch on one corner caused it to do cartwheels.

[Sam Stone]

Wouldn't shooting a rocket off of a hydrogen balloon generally be referred to as a "bad thing"? ;)

But more seriously, exactly how big would this thing need to be to support the weight of a full rocket?

How much does shooting from a higher point save us in terms of weight?

If you're that far above most of the atmosphere, does that mean that the balloon would be stable enough to support something like this? I would be worried that without much atmosphere, even if there was no wind, that any change in weight on any point on the surface would cause the whole thing to bobble and lean. There just wouldn't be much stabilizing it. I wouldn't want to shoot a rocket off of something where the lightest touch on one corner caused it to do cartwheels.

You're not shooting off a rocket. That's the whole point. You're floating your way to orbit. You create a balloon that looks kind of like a big V. It's miles across, and must be assembled at 140,000 feet because it wouldn't be strong enough to withstand weather. You put an ion engine on this. You get aboard from your floating space station, and cast off. It starts to rise very slowly in the rarified atmosphere, but it does rise - to about 200,000 ft. As it rises, you light your ion engine, and start it moving forwards. As it goes faster, lift from the few molecules it encounters push it higher. You keep accelerating, and as you go faster and faster, the balloon goes higher and higher. Eventually, you are going fast enough to reach orbital velocity, and voila, you're in orbit.

To come back, you decelerate very gradually. The thing slowly sinks, and as it does it starts to encounter the tenuous atmosphere. Now you use a balance between drag and your engine to slowly transition from orbital speeds to 'flying' speeds, and then float back down to the station hovering at 140,000 ft.

The thing encounters the atmosphere so slowly and decelerates so gradually (days instead of minutes) that it never gets hot. It needs no heat shield, and is not subjected to any real stress. As an astronaut, you'd simply see the earth gradually getting larger, and over a period of five days you'd gradually feel gravity building until eventually you were just a guy floating down in a balloon. Very safe. Almost cost-free. And only a tiny fraction of the fuel is required because you're leveraging the atmosphere to buoy/skip you into space.

There are still lots of questions to answer about this, having to do with how much payload it could carry, whether it could carry the weight of the engines it would need, whether it can handle static building and other stuff like that. But compared to the problems of building and maintaining a space elevator, this is nothing.

[[Undecided] Adrian]

How do you want to accelerate a huge balloon with an engine that develops only 5 N of thrust continuously with an enourmous power requirement (http://en.wikipedia.org/wiki/Ion_thruster)?

[Lumpy]

I've always heard that the orbital balloon concept would use plasma engines, not ion. I still couldn't tell you what sort of thrust/weight ratio they have.

[smiling bandit]

If you really wanted to get into space cheap, build a nuke plant, an extremely powerful laser fed off of it, and use laser-confinement acceleration to shoot a spaceplane up. It can come down under its own power.

Or build a giant magnetic-accelerated railgun, with the added benefit that you can do it anywhere and not just at the equator, and do the same thing.

[BrainGlutton]

. . . laser-confinement acceleration . . .

How does that work?

[ENugent]

Look, here's an incredibly optimistic paper (http://www.liftport.com/papers/2005Nov_LP-Ribbon_Mass.pdf) (pdf) written by a guy who works for a Space Elevator Booster corporation. (Get it, booster?) Check out Figure 2. CNTs have a density of between 1.3 and 1.4 g/cm3, which puts us between the yellow and the green curves. (If we build it out of water, we can use the red curve.) According to wikipedia, in 2000, somebody built a nanotube that measured a tensile strength of 63 GPa. This seems to be a reference to this paper (http://www.sciencemag.org/cgi/content/abstract/287/5453/637). (abstract only) You'll note that the tubes ranged in tensile strength from 11 to 63 GPa, although 63 GPa is the figure which seems to be cited as the "tensile strength of CNTs". You will also notice that this was not a test on a macroscopic scale. The entire testing apparatus fit into the imaging chamber of a scanning electron microscope. (That is, it 'tweren't very big.)

Back to the point, referencing figure 2 of the incredible optimistic paper, we see that if we have a tensile strength of 50 GPa we're talking about a mass of between 400 and 700 metric tons. (I'm estimating the green curve, obviously, but it looks to be a bit larger than 1.5 times the yellow curve, and both curves ought to be exponential.) That's if the cable can uniformly withstand 50 GPa and we accept a factor of safety of 1. If the cable is weaker, the situation only gets worse, of course. (Remember, this is the graph which gives bare minimum masses supplied by the true believers who think the whole thing can be put into operation for only $1B.)


The author no longer believes that a space elevator will be built on Earth any time soon, as I understand it from dinner table conversation. (He's my husband.) He gave a presentation at the last Space Elevator conference (http://www.spaceelevatorblog.com/?p=1005) on the reasons why not. I think he does think that it is still feasible for other planets when we get to the point of permanent bases there - the numbers work out much better for a lighter planet. I tried to get him to join the discussion here, but he's way too busy (http://www.lasermotive.com/blog/) right now.

[ENugent]

Oh, he was also amused by the "incredibly optimistic" characterization, since he was being so much more pessimistic than most of the space elevator community when he wrote that paper.

[smiling bandit]

How does that work?

It's actually quite ingenious, and coiuld probably be built with modern materials. You create a "bottle" on the hind-end of your spaceship. The bottle can be made to self-stabilize, so the ship automatically stays in line with the laser. The energy does heat the sucker, but most of the energy actually floods back out, shoving it forward. The downside is that you need a monster power plant and a laser with a lot of juice running through it ... but that will come in handy when the Evil Asteroid of Doom comes to Sprinkle Zombie Powder and Harbinge Our Alien Overlords.

More seriously, there are big engineering challenges, but they are a lot more practical than building a space elevator. I favor the magnetic-acceleration launcher system more, though.

Another issue with the "space elevetaor" is that the sucker with resonate. At two freqeuncies. Get it slightly wrong, and you'll rip the thing to pieces just running a shuttle up and down.

[Chronos]

Another issue with the "space elevetaor" is that the sucker with resonate. At two freqeuncies. Get it slightly wrong, and you'll rip the thing to pieces just running a shuttle up and down.Only two? A taut string has an infinite number of different resonant frequencies. Still, though, it's the narrow resonances you're trying to avoid, not the broad spaces between the resonances. So if you plan to be off resonance, and get it slightly wrong, you'll almost certainly still be off resonance.