Space Elevator Could Cost Less Than You Thought

WolfWithoutAClause writes: "We've had Space Elevator stories before on Slashdot, mainly saying how impractical they are for the foreseeable future. Now however, there's an 8M pdf paper on NASA Institute of Advanced Concepts [NIAC] website that says it may now be possible with existing materials and can be done for about $40 billion. That's less than the entire launch market for a single year. If he's right, the first elevator may be complete in 10 years time, with the second and third following 2-3 years afterwards."

Comments

9/11

[Anonymous Coward]

Not to bring up any bad memories, but if history has taught us anything - this will be a target. How could you keep something this long and lanky safe from planes?

Re:9/11

[WolfWithoutAClause]

Surface to air missiles and/or aircraft.

Re:9/11

[xah]

Who marked this post as flamebait? It makes a legitimate point.

Among others, this "space tether" would be vulnerable to the following terrorist attacks: missle, bullet, bomb, acid, human piloted aircraft, remote controlled aircraft, ground vehicle, laser, and fire.

These are just a few of the feasible methods to cut such a cable. If a terrorist wanted to place an infiltrator inside the space elevator, more attack options would be available to them.

This space elevator idea doesn't sound feasible when the security problems it would engender are considered.

Re:9/11

[Suidae]

Don't forget one of the more obvious attacks, building a fuel-ladden craft that is to be raised on the elevator and which just happens to detonate while being raised. Depending on how tough the climbers are cable are, and how well protected the cable is from other attacks, it might be a practical attack channel.

Re:9/11

[Sideways The Dog]

That's why we should build the first one in Iraq.

Re:9/11

[Anonymous Coward]

Flamebait?? Space elevators - huh...!

We have the technology to consider space cables, but not to understand that, hello, GOD isn't REAL! Nothing supernatural IS!

GOD, if you exist, prevent me from posting this RIGHT NOW!!

YES, this is MEANT as flamebait!! Get rid of religion and force the Bin Laden's to use alternative methods to "convince" their followers...might be trickier that way...

Re:9/11

[Anonymous Coward]

Poor you

Re:9/11

[Anonymous Coward]

Offtopic but ...

What is natural? What is supernatural...

Whatever you can predict becomes natural? Why are there electrons, quarks, gluons and what ever? How much natural is all that shit?

Of course, we "run" under some kind of rule based system we'll eventually descipher. But claiming we'll then know god doesn't exist is like Pac Man claming we dont exist because he has figured out all the secrets (that movement can be right, left, up, down, and that not all 4 directions are available all the time. And that eating or "going through" "ghosts" get you killed unless you eat the "Pil". And that act shapes a new path blocking surface).

We can undestand 100% of the physic world, yet the mistery will remain.

As somebody else said...poor you

Re:9/11

[aprosumer.slashdot]

This would not be a target for terrorists because a space elevator would not be a symbol of US foreign policy.

Re:9/11

[fireheart17]

You do make a good point that as long as it were not a symbol of policy or oppression then it would be safe. However, if such a structure were built and maintained by the US and somehow used to advance policy it could become a target in the future.

Re:9/11

[Ifni]

You make the dangerous assumption that all terrorists have the same agenda, or indeed, that the trrrorists responsible for the 9/11 incedent have only one beef.

If you believe the US propaganda (which I neither deny nor condone), Al Qaeda is against all forms of personal freedom, and indeed against western culture and commerce (or even, simply, non-Muslims). If any of this were true, why not destroy such a pinnacle of Western technology? According to statements from various sources (Taliban and Al Qaeda sources as quoted by Afghani news sources), the triumph of the Sept 11 attacjs was that the world knows that America isn't invincible. The same point, in their mind, would need to be proven regularly, to set it in the mind of the citizens of the world that NO place was safe (and, by extension, that no act is unthinkable).

And that's just Al Qaeda. What about some other religious whackos that decide that this structure is an affront to God (a Tower of Babel, if you will)? Indeed, no matter who builds it, it will be a target, just on account of its prominence.

There are certainly ways to defend it, though they won't be foolproof. At least a one mile radius area around it will need to be a no fly zone, and fitted with sensors to deter unauthorized intrusion (since it will be in the middle of the ocean, this means sonar detectors able to detect people - indeed, probably some sort of underwater barrier around the whole mess). Costly, indeed. And yet, like most security in place currently, only as reliable as the people who operate it...

Re:9/11

[An Onerous Coward]

Good analysis. I'm sure that as soon as space becomes more accessible, some sort of "anti-Space" movement would erupt, whether for ecological, religious, or political reasons. Whatever the case, somebody's going to want to bring the thing down.

What I think everyone has been missing so far is that we're not talking about a cable that stretches from sea level to geosynchronous orbit. The proposed project is an itty-bitty, free floating cable only a few hundred miles in length. The extensive security measures you describe would be absolutely necessary for a giant cable, but not for the elevator being proposed.

Re:9/11

[An Onerous Coward]

Okay, I'm an idiot, and should be moderated accordingly. While I was waiting for the PDF to drip in from my 28.8 modem, I was reading some of the links that the survey author had put up. Most of the reasonable sounding ones were describing relatively small projects a thousand miles in length or so. The PDF itself does indeed go all the way from ground level to geosynchronous orbit.

Did I mention I'm an idiot? Okay, just checking.

Re:How about....

[Anonymous Coward]

It's doing fairly well, at least if you're downloading from Internet2:

03:36:54 (70.09 KB/s) - `521Edwards.pdf' saved [9088310/9088310]

However, Slashdot can't seem to handle the load. For the last few hours I couldn't log in, half the links sent me back to the main page, and the server wouldn't respond for long periods of time.

It's a tether

[Dr. Tom]

This version of the Space Elevator doesn't go all the way to the ground. That's why it can be built with existing materials. You still need a (hydrogen fueled) rocket to get to the dock at the lower end of the tether, which is about 250 km up. However the dock is moving significantly slower than orbital velocity, which increases payload and allows cheaper (more reliable & maintainable) rockets.

Re:It's a tether

[bofh31337]

A full 35,000km long space elevator would not be practical. Something of that great length would span many g-forces and you would need a large counter-weight above geo stationary to have zero velocity at ground level. Having that kind of taper from bottom to top would require a huge mass The big difference with a 250km tether is the center of attracting (and mass for that matter :)) can be in many more places. I'm thinking the best idea isn't so much a space elevator but a space slingshot using a pair or more of gravity stabilized fully rotating cables. It's an interesting idea that's been thrown around for many years.

Re:It's a tether

[WolfWithoutAClause]

> A full 35,000km long space elevator would not be practical.

That's what I thought, but read the paper. He claims it's possible; and describes how, how much and how long. The carbon nanotubes are strong enough now; or atleast that's the claim.

Re:It's a tether

[JohnPM]

Not sure you were reading the same document as I was. The cable certainly does go all the way to the ground. Also, the cable described cannot really be built with existing materials because it relies on carbon nanotubes. While this material does exist, I don't believe it has ever been used as a construction material outside the laboratory.

Re:It's a tether

[JabberWokky]

While this material does exist, I don't believe it has ever been used as a construction material outside the laboratory.

NASA may have its current problems, but it has a beautiful history of advancing materials science and using labratory materials in real world situations with incredible results. I do not doubt that if they set out to do this, and choose to use carbon nanotubes, that not only will it be built, and carbon nanotubes become a practical building material (in whatever level of expense they wind up settling at), but also that the public as a whole will forget that it was NASA that spearheaded the practical use of the material, and will continue to perpetuate the myth that NASA spent our tax dollar developing zero G pens while the Soviets used pencils.

--
Evan

Yes, it does go all the way to the ground

[iktos]

It's about a 96000 km, fixed at the bottom end, with a counterweight at the far end.

It's 50 mm wide and with a cross section of 2 mm^2 (which makes it good for lifting 20 tons, payload 12, every 97 hours). But upgradeable, of course. Cable mass 572 tons, counterweight 621.

Many parts of the building are pretty well thought out, like first sending down a thin cable and build the rest by having climbers adding more, and then using the used climbers as the counterweight. (Also, the climbers increase in mass as the cable grows stronger, from a total of 619 kg to 20 tons. Beam powered from the ground.)

The initial cable would mass 19.8 tons, with fuel the deployer would mass 190 tons, but that's still a reasonable number of Shuttle missions.

Re:Yes, it does go all the way to the ground

[Anonymous Coward]

One of the interesting things about this design is that the counter weight must be in a strange state of having superorbital speed.

Take the differential element of the wire that sits at the geostationary orbit. That element sits in geostationary orbit, and would be weightless.

The thing is, all points on the wire would have to have exactly the same orbit time, if the wire is to stay straight.

The counter-weight would ALSO have to have an orbit time of exactly one day. This means that it would be moving faster that objects would naturally at that orbital radius. How would that be done? By having the wire support tension, just like flinging the counterweight around on the end of a string under tension.

The base of the wire would have to be attached to the earth in a very strong manner to support that tension.

A nice pair of scissors would send the counter-weight into a very large orbit indeed. :-)

Re:Yes, it does go all the way to the ground

[Anonymous Coward]

would not the gravitational force on the cable cancel most of the tension from the orbiter?

Re:Yes, it does go all the way to the ground

[Anonymous Coward]

Climbers will add more cable, and then the climbers will be part of the counterweight?

Are there that many suicidal volunteer mountain climbers? Or is the counterweight area actually a huge bar and hotel for the climbers to hang around in for a long time?

Re:Yes, it does go all the way to the ground

[An Onerous Coward]

Not quite. If the counterweight is traveling faster than it should at that orbit, that doesn't mean that it would be launched away from the earth. Climbing the Earth's gravity well sucks away an object's kinetic energy. Unless the counterweight were traveling faster than escape velocity (for its current height above earth), it wouldn't go anywhere.

But...

[Not2Bryt64]

What happens when this thing grounds the ionosphere? Prolly a stupid question, as I don't actually know if this is even possible, but I am curious to know if anyone else does.

Re:But...

[Unknown Poltroon]

David Gerrold (sp) just wrote a book a called jumping off the planet, basically set on a space elevator. One of the uses of the elevator is generating MASSIVE amounts of electricity from this sort of effect, which has to be managed by seling it, giving it away, or simply grounding it. Not a bad book set for the young to teenage coming of age story, but enjoyable by an adult.

Re:But...

[WolfWithoutAClause]

That would probably be bad, although it might sort itself out, I don't know if anyone really knows what happens. I think that the tether would be designed to be an insulator.

Re:But...

[Anonymous Coward]

Okay, I know it is in poor taste to criticize grammar on discussion boards, but I'm so sick of /.ers not knowing that the word is "probably" and not "prolly".

Sorry...

Re:But...

[Anonymous Coward]

I know this is in poor taste and poor parody, but for ciritizing an abbreviation like 'prolly', you should really consider using Slashdoters, instead of /.ers.

Previous posting on this

[iiii]

Yes, it's a tether, and previous articles about it have been posted before.

the paper, not the slides

[blamanj]

That 8M download only gives you the slides - pretty pictures but no text. The actual phase I paper is here. It's a 15M download - and you can year the server creaking under the strain.

Re:the paper, not the slides

[WolfWithoutAClause]

Actually, to be correct; the 8M pdf file is the phase II paper, which was written later; and contains more information if anything; but less text.

I dont think the insulation matters.

[Unknown Poltroon]

I still think youd have to dealwith charge differentials, like with static electricity type of things. But I al also talking out of my ass now.

Angular momentum

[p3d0]

When something's going up the elevator, where does it get all the angular momentum it needs to stay in orbit? Does the climber have rockets? I don't see them on the diagram.

Re:Angular momentum

[Anonymous Coward]

As you go up the wire, there you would have to hold on not only vertically, but also horizontally in proportion to your vertical speed. That is... if you were holding on to the wire for dear life, but not moving, you would only have to counteract the local gravity, whatever that was. But as soon as you started moving vertically, you'd have to hold on to the wire horizontally. It's the reaction force to that force that gives you your angular momentum. The faster you climb, the higher your horizontal force. In principle you could climb it without a rocket, but in this design, they use a free electron laser to beam power to an ascending pod.

Re:Angular momentum

[p3d0]

Ok, thanks. But doesn't that impart equal and opposite angular momentum to the cable? What happens to that momentum?

Re:Angular momentum

[RevCheswollen]

I think it'd be rather like climbing a very tall tree, at least until the air got thin. If the tree isn't strong enough, it fails. Otherwise, you are just more wind.

Re:Angular momentum

[PhuCknuT]

I'm a little drunk so ignore me if i make no sense. I would think that every object that climbs the cable would impart angular momentum on the cable in the direction opposite the rotation of earth. The mass of a single "launch" would be miniscule compared to the total mass of the cable and counterweight, so it wouldn't cause much motion in the cable. Since the cable is essentially hanging like a giant pendulum off the earth, the "top" end of it would slowly swing back and forth in orbit. All you have to do to stop each launch from adding to the motion of the cable, is to time each launch to coincide with the cable swinging in the opposite direction the momentum that the launch will give it.

I think that makes sense.

Re:Angular momentum

[p3d0]

Perhaps. It still feels like we're getting angular momentum for free here. It's like we're neglecting the biggest coriolis effect on the planet.

I think when a weight goes up the rope, stealing some of the rope's angular momentum, the rope will not swing like a pendulum as a result. Rather, it will very, very slowly wrap itself around the earth.

Re:Angular momentum

[CedgeS]

You are probably not thinking about angular momentum, but energy in circular motion.

Energy contained in circular motion is equal to:
(This is the energy associatied with angular momentum)

E = 1/2 I * (w^2)

Where I is the moment of inertia and w is the angular frequency (in this case about 7.27 x 10^-5 1/s because the period of rotation will be 24 hours). The moment of inertia will increase as the load gets further away from the Earth.

I = m * (r ^ 2)

m is mass
and r is radius from the center of the earth.

So, the energy in circular motion at each height would be:

E = 1/2 * m * (r^2) * (w^3)

To get the formula for the total energy at each height, add the potential energy from Earth's gravitational pull.

To answer your question, the increase in angular momentum of the payload is a result of the force exerted by the elevator doing work on the payload, resulting in a change in energy of circular motion.

If you are worried about what is called conservation of angular momentum, the increase in angular momentum comes from a decrease in the angular momentum of the Earth. Conservation laws are usually written like so:

initial = final

So,
L (angular momentum) initial = L final

I forgot, angular momentum = I * w

Where L is the sum of the angular momentums in the system.

So,
L(earth) + L(payload) + L(elevator) initial = L(earth) + L(payload) + L(elevator) final

Because the radius from center of mass of the elevator and the Earth don't (negligibly) change during the lifting of the payload (this would affect I) and that for the payload does, the final angular frequency of something must be slower. Since they are all tethered together going at the same angular frequency, their angular frequencies must remain the same, and the anular frequency of the Earth will decreas very slightly (negligibly actually) and days will become slightly shorter while the payload is in space. You wouln't notice it though, because this happens every time any payload is sent into space -- every satellite space ship, etc.

When you drink too much physics, alchohol just doesn't make any sense anymore.

Re:Angular momentum

[PhuCknuT]

Well the angular momentum isn't free, it's taken away from earth's angular momentum. If we were to launch a significant percent of earth's mass this way, we could make a day longer. That would require billions of launches though, so i don't think it's a problem. :)

The reason it won't wrap itself around earth is that the counterweight at the end of the cable is not in orbit, it's actually moving faster than the orbital speed and being pulled centripitally by the cable. I'm not sure how many g's it would be pulling, but you should be able to stand on it and look up at earth. And since the g force is in the direction perpendicular to the earth at the anchor point, whenever it swung away from vertical there would be a component of the cable's tension pulling it back towards vertical again. Hense, a giant pendulum.

With the huge length of the cable and mass at the end of it, the period of the pendulum would be pretty long probably. In order to have the launches cancel out each other's effect on the cable, the launch frequency would have to be a multiple of the period of the swing. Maybe that's how they came up with the 97 hours between launches?

Re:Angular momentum

[JohnPM]

Yes, finally nested 6 or 7 deep the correct and simple answer to the question. The angular momentum comes from the Earth.

As a payload climbs the cable its angular momentum is increasing. This is initially transferred to the cable which may or may not pendulate. However since the cable is pulling upwards under centripetal acceleration, it will eventually transfer its extra angular momentum to the Earth.

I don't agree however that you could cancel the effect out by timing the subsequent launches. The issue of total angular momentum needs to be addressed. Subsequent launches could only cancel the angular momentum if they were somehow launched from the end of the cable with opposite angular momentum.

We can consider the total angular momentum to be a conserved scalar (keep everything moving around the Earth's axis). As a payload climbs the cable its angular momentum is increasing. Consequently the angular momentum of the cable is decreasing, so it lags behind the Earth (very very slightly). Having just read the full 15Mb document, I don't think was discussed anywhere. My guess is that the cable would lean very slightly to the west more or less permanently while you are sending up payloads. In this state the cable would also be pulling up and to the west on the mooring station, which would bleed off some angular momentum from the Earth (but never enough to measure). If you stopped sending up payloads the cable would gradually straighten. I'm not 100% sure how the converse case works (when payloads come down the cable). But one thing discussed in the thesis is how gravity applies a torque to the cable when it is not perfectly vertical. In this case an equal and opposite torque is applied to the Earth through gravity.

Re:Angular momentum

[p3d0]

You are probably not thinking about angular momentum, but energy in circular motion.

Perhaps, but I really think I'm talking about angular momentum.

To answer your question, the increase in angular momentum of the payload is a result of the force exerted by the elevator doing work on the payload, resulting in a change in energy of circular motion.

How can you get angular momemtum arising from forces that act perpendicular to the direction of the desired orbit?

If you are worried about what is called conservation of angular momentum, the increase in angular momentum comes from a decrease in the angular momentum of the Earth.

The cable is not rigid, and unless I'm mistaken, it is perpendicular to the Earth's surface, so I don't see any way it can transmit a moment to the Earth.

Re:Angular momentum

[p3d0]

My guess is that the cable would lean very slightly to the west more or less permanently while you are sending up payloads. In this state the cable would also be pulling up and to the west on the mooring station, which would bleed off some angular momentum from the Earth (but never enough to measure). If you stopped sending up payloads the cable would gradually straighten.

Ah, yes. Now that makes sense. Thanks!

I just wish I had read this before I posted that other reply that assumed the cable was perpendicular.

Re:Angular momentum

[PhuCknuT]

I don't agree however that you could cancel the effect out by timing the subsequent launches. The issue of total angular momentum needs to be addressed. Subsequent launches could only cancel the angular momentum if they were somehow launched from the end of the cable with opposite angular momentum.

I think you misunderstood what I meant. The cable would lean west (very slightly) during a launch, and once the payload finished its ascent, the cable would swing back towards vertical. If left alone at this point, it would continually swing back and forth. It's not the transfer of angular momentum away from earth that I was talking about cancelling, it's the swinging of the cable. If you time your launches so that they occur while the cable is swinging back east, the eastward momentum would be canceled out by the westward momentum that the cable gains from the cargo.

As for why it would swing like a pendulum, I'll try to explain the best I can without drawing pictures. :) As long as the cable is leaning westward, the cable will be gaining eastward angular momentum from the earth. This is simply because the cable is under tension and no longer perpendicular to the orbit. Likewise, when it leans east, the cable tension will have a westward component pulling on the counterweight. As the cable swings back and forth, the angular momentum of the whole system (earth, cable, counterweight) will remain the same, but a small amount of the momentum will slowly transfer back and forth between earth and counterweight.

Re:Angular momentum

[PhuCknuT]

That first paragraph was supposed to be in tags, guess that will teach me to not preview first :)

Re:Angular momentum

[Fishtank]

Just guessing, but the angular momentum is presumably bled off the angular momentum of the elevator, in the same way that extending your legs whilst in a spinning office chair works.

This is presumably a problem unless you then bring equal mass back down the elevator - why has nobody mentioned imports (people, rocks, deep frozen boze condensates, perfect diamonds and mass produced statues of aliens made out of 'genuine 100% space rock') here?

Re:Angular momentum

[Sir Runcible Spoon]

Looking at the slides, the climber appears to be powered from the ground by laser. Maybe they plan to power the elevator in the same manner. Hopefully it would not fry the contents or melt the cable.

Re:Angular momentum

[WolfWithoutAClause]

> The cable is not rigid, and unless I'm mistaken, it is perpendicular to the Earth's surface, so I don't see any way it can transmit a moment to the Earth.

You're exactly right. It can't be perpendicular to the earths surface and transmit moment to the Earth.

In fact, as an object goes up the tether, it tends to drag the tether to the west, because the tether is accelerating the payload sideways as it goes up towards orbit at geosynchronous altitude- it needs a few klicks/sec up there relative to the ground, and its stationary at ground level, so it accelerates as it goes up the cable. The only way a cable can do that is to form a shallow v shape.

This V shape means the tether is tilted to the ground. The tension on the tether at the ground will therefore pull on the earth and slow it down; but I wouldn't exactly lose sleep over that bit.

In fact, the tether's position can be controlled by moving the payload up and down on the tether and careful timing.

Re:Angular momentum

[p3d0]

Ah, very good. That makes sense. Thanks!

Re:Angular momentum

[JohnPM]

I agree generally with what you're saying. It's interesting that this discussion doesn't seem to have come up much in Edwards' report. One thing he advocates is using a floating platform like the Boeing SeaLaunch. This would allow you to move the cable out of the way of space debris on an hourly basis and away from storm systems. However the angulam momentum issue would cause an overall westward pull. The total impulse involved would be comparable to the impulse applied to the cargoes (ie. they're heavy payloads being given planetary transfer velocities), so the platform would need to be pushing east all the time in order to maintain position.

Just to summarise how I understand the angular momentum issue now: When a payload is launched its angular momentum is increased by, say, A. This is taken from the cable, causing it to lean west slightly. As it leans west it will transfer its angular momentum to the Earth via both the coupling with the ground/sea and via a correcting gravitational torque (which of course acts equally and oppositely on the cable and the Earth). The cable will then pendulate east and west, transferring angular momentum back and forth between itself and the Earth. If left in this state I suppose the oscillation would eventually dampen out from friction with the atmosphere and from induced currents in the cable as it moves through the Earth's magnetic field. This may well take millions of years though. If you then time a subsequent launch (when the cable is swinging east, say) then you can stop it in the vertical position, cancelling the oscillation. At this point the cable will have transferred 2A units of westward angular momentum to the Earth.

It may well be however that these issues are not a consideration for designers. If the induced oscillation is small enough then you could simply launch whenever you like and you would be increasing the oscillation about half the time and decreasing it the other half of the time. Overall it would be very unlikely that a problem would develop.

more info

[CowNutsMack]

heres some more info on it

It's a bit more robust than you think...

[Anonymous Coward]

First of all, if you break the cable down low, the bulk of it just "springs back" into an elliptical orbit with the same perigee.

Secondly, a lot of plans call for the cable to join a 15 km high tower, since building up from the earth is feasible for that altitude, and chopping mass off the bottom end of the cable translates directly to increased cargo capacity. 50,000 ft is higher than most planes fly.

The scary scenario is the cable breaking up high, e.g. the counterweight coming loose. The cable would fall to earth, wrapping around the equator multiple times as it does so, cracking like a whip. All of the energy spent launching it would come down in a long thin bang.

Re:It's a bit more robust than you think...

[boldra]

The risk of enormous destruction, I think, is a pretty good reason why sabotage is less likely to happen.

Sure, I was surprised that the September terrorists were obsessed enough to kill thousands of people, some of who were their countrymen. But I think that the chances of any individual being prepared to do such a tremendous amount of damage to so many countries (Africa would be the worst hit) is slim.

Maybe I'm optomistic. I know there are evil people around, but I can't imagine anyone wanting that much indiscriminate death.

Anyway, I don't believe the risk is a show-stopper. Various possibilities, such as a self-disintegrating cable, quadrouple thickness, extraordinary security etc mean that this will one day be reality.

Re:It's a bit more robust than you think...

[An Onerous Coward]

I got really, really suspicious when the article summary said we could have a space elevator for $40 billion. I said to myself, "Self, there's just no bloody way." And I was right.

What the author of the study is proposing is a small elevator that takes things from the upper atmosphere to a point several hundred miles higher. This small scale is what makes it practical, and what makes it possible to propose such a thing without bringing up ugly images of an equator in flames.

What would be really cool is a series of these small elevators, each pulling cargo up higher. It would be a great deal more fault tolerant and less risky than a single, monolithic elevator. It might also be a logistical nightmare. Further study would be required.

disaster

[xah]

At some point the cable would come loose from the counterweight. Maybe a meteorite would hit the counterweight, or a terrorist would cut the cable from that high location, or the fastener would simply give way. In any case, a worldwide disaster would result.

The cable would fall to Earth. It would wrap around the Earth several times, as pointed out in another post below. The cable would stretch across continents, oceans, roads, railroad tracks, lakes, rivers, cities, residential areas, wildlife preserves, and many other areas. Thousands if not millinos of people would likely perish. It is conceivable that the entire Earth would shudder, literally.

This is a project that should never be built.

Re:disaster

[Anonymous Coward]

oh puh lease. 1 1000 ton weight making the earth shudder ? you gotta be kidding me. millions of people perishing ? the cable will just burn up in the atmosphere.

Re:disaster

[Anonymous Coward]

The fact is, we have no way of predicting exactly what would happen. The cable would not necessarily burn up in the atmosphere if it comes down slowly enough. If the cable survived enough to wrap around the earth several times, depending on the tensile strength of the cable, there could be a variety of disasters, as hydroelectric dams break, tsunamis are generated, buildings crumble, nuclear power plants break open, and, quite possibly, cable pieces fly off in random directions all over the world in a shrapnel effect. As transportation routes get cut off, food sources could be cut off and people could starve. Millions of deaths is quite realistic.

Re:disaster

[Anonymous Coward]

One reason why the cable might NOT burn up in the atmosphere would be that, as a heat conductor, the heat generated by re-entry would be distributed throughout the cable, lowering the overall temperature of the cable and reducing the likelihood that any part of it would burn up.

Re:disaster

[Anonymous Coward]

This scenario has been beautifully described in Robinson's "Red Mars". Get a copy and read it - it's fascinating.

Re:disaster

[Anonymous Coward]

We used to tension high tensile cables for suspended slabs in high rises.

The cable would be anchored at one end, and then pulled at the other, and finally swedged off, to keep the tension. The sheaths were lubed to assist the stretch.

We would be doing this on the side of a multi-story building, 10 or 20 floors up. Every so often, a cable grip would fail, and the cable would shoot out the other side of the building, like a giant metal snake. All of the tension (stored energy) would make it shake and sing as it zoomed off to another part of the city.

We paid off quite a few broken windows, etc. We used to joke about targeting banks and insurance buildings.

It reminded me of a giant cross-bow...very dangerous.

In the case of a giant teather, attached to a spinning ball, you have to consider that the cable itself would want to simply coil back down against the planet. It's weight alone would cause it to drop vertically, as opposed to floating around in the atmosphere, and/or travelling to another part of the planet. Anchor it on the equator, in the middle of the ocean, on the sea bed. When/if it comes loose, any energy will literally be absorbed by the water.

Invisible men who live in the skare not natural...

[Creedo Kid]

Thinking that that invisible man really cares and loves you because he lets buildings fall on yoiur head is also "not natural"

Invisible men in the sky=not natural

[Creedo Kid]

uhh sorry...

Popular Idea

[TACD]

Surely the demand to use this thing if it was ever built would be incredible. Everyone and his auntie would want an observatory up there, NASA would want to launch shuttle missions and whatnot from it, and many many multinationals would want to set up services to take people up on trips.

Not only that, but how would waste (of all sorts) be disposed of? It seems an ENORMOUS pipe would be required to take everything down (although launching it into space would be simple, I suppose); and an even bigger pipe needed to pump up water and oxygen (with an equally huge compressor at the bottom to pump it up).

I get the feeling that comments about it crashing into satellites and creating mountains of space junk are nonsense, but I also get the feeling that not many countries would be too pleased at America having a platform attached to land (or not; whatever) from which to spy on and potentially launch attacks from. It's sort of one step up from the spying capabilities of satellites, but I can't see all countries having space elevators very soon (though that would be cool).

I' done with my ramble. Rip into my logic noww, please do. Destroy my sense of self-worth. ;)

Re:Popular Idea

[An Onerous Coward]

The pipeline going down would invariably be smaller than the pipeline going up, and everything sent down the pipeline would end up saving energy, because it would balance a load coming up.

America--and most other countries--will never have its own elevator attached to land, because a land-based one would have to be geosynchronous. Therefore, it'd have to be located on the equator. The one described in the paper is more free-floating, and would most likely either be located over the equator or spend time over most countries. In either case, the thing would be too easy to shoot down.

What kind of crack cocain are you smoking?

[NDPTAL85]

You actually think common sense will be enough to safegaurd it? The fact that destroying it would be a "very very bad thing" is enough to deter everyone? Did you even _think_ about the nutjobs in the world?

I see some major overlooked features...

[szyzyg]

Firstly - they seem to have ignored the fact that a cable this long would snap under its own weight - even made of this carbon nanotube material. Ideally you want to maintain a constanst strain on the material throughout the tower so you need to start with very thick cable at the midpoint then taper it out towards the ends - the midsection would be maybe 10 times thicker.

Now, even if they've accounted for this then the depolyment is in trouble, since they have to spool out the material from a drum, which means that you start spooling from one end or the other which means that you can't follow the ideal thickness profile without exceeding your structural limits during some point in the unroll procedure.

The design for the deployment should instead extend the upper and lower half in both directions simultaneoulsy. The problem here is desiging a mechanism which can deploy this towards the end when the strain becomes highest.

Another minor issue is how quickly you can deploy such a a large sturcture - the more patient the better, but you're dealing with 100,000km of cable - taking at at 10km/hr would take over a year to deploy, acceleration and deceleration of the deployment would induce oscialltions in the cable which would be difficult to damp...

As for the danger of a break - not only would it fall down by wrapping itself around thew world a couple of times, but the tension on the structure would be like a strethed rubber band - the stored energy would be huge - think in terms of a nuclear powered rubber band.

Re:I see some major overlooked features...

[JabberWokky]

Now, even if they've accounted for this ...

Why don't you get a physics degree and submit your own paper.

Or, here's a netball, left field idea - read this paper, see if you understand the math involved, and if not, drop back, read a bit more, figure out what we've learned about orbital mechanics, structural engineering and materials science over the past 8,000 years, and apply Clarke's second law.

--
Evan "Armchair physicist who knows where his knowledge ends and learning begins" E.

Re:I see some major overlooked features...

[Anonymous Coward]

Oh, well I have a Physics degree. This stupid idea won't work. What is it with you slashdorks? You all seem to get raging erections when ever this space elevator idea comes up.

No practical materials to build it with.
No way to fund such insanity.
The real risk of a failure is toooo high.
I suppose you will want to be the one to be under the cable when it snaps and whips around the world 4 times releasing hydrogen bomb amounts of kinetic energy?

Re:I see some major overlooked features...

[An Onerous Coward]

Man, do you even have the foggiest idea what you're talking about? You keep mentioning 100,000 km of cable. That's not what this guy is proposing. The "ideal cable" stretching all the way from ground zero to geosynchronous orbit is still a sci-fi dream, and you're insulting the guy by saying he's too stupid to realize that.

The cable he's proposing is a much smaller one that would carry payloads from the upper atmosphere to a point a few hundred miles higher. There's no "wrapping itself around the world a couple of times." Just a nice, efficient little elevator for reducing the cost of moving materials into orbit.

Re:I see some major overlooked features...

[An Onerous Coward]

Man, I don't have the foggiest idea what I'm talking about, and I certainly had no right to go blasting you like that. In fact, the proposed design does go all the way to the ground, and I was stupidly conflating this project with a less ambitious one I'd read about earlier.

I still think that you're insulting Mr. Edwards by saying he wouldn't have taken into account the fact that the cable would have to support its own weight. However, after looking through the PDF, it's not beyond the realm of possibility that the guy is just a kooky graphic design major. He sure didn't provide a whole lot of detail.

Re:I see some major overlooked features...

[JoeGee]

I suppose you will want to be the one to be under the cable when it snaps and whips around the world 4 times releasing hydrogen bomb amounts of kinetic energy?

On top of the Galapagos Islands, to boot. Not very eco-friendly. :)

Falling down

[Anonymous Coward]

Could you imagen this falling down.

"To night at 10: Just this after noon the space elevator fall taking out florda, Damit no more election scandels"

The new God

[Anonymous Coward]

Something like this could actuly start humanity into space. I know space has very little economic value it could provide a unifing goal for most of the wold. This would in turn reduce profity and give something for thirworld countrys to do.

Red Mars, Green Mars, Blue Mars (Trilogy)

[reptilian biotech]

Some great sci-fi reading, by Kim Stanley Robinson, has quite a bit about space elevators in it, and for all you who wish there were some type of utopian government... the problems that arise from building a society on mars. Excellent reading...

Re:Red Mars, Green Mars, Blue Mars (Trilogy)

[JoeGee]

I agree, this is some of the best hard sci-fi ever written. On an aside do you know what happened to Fox's purchase of the film rights of the trilogy? I had heard it was being adapted as a miniseries for TV, and then the buzz died down and I haven't heard anything else about the project.

My only problem, the reliability ...

[JoeGee]

... of current launch systems. Do we want and can we really afford to build redundant anchors, redundant cable spinners, etc.?

We cannot even guarantee that a shuttle, or an Arianne, or an Energia will launch on a given date, or even that once it launches its payload will arrive at its intended destination. We have the technology to boost this kind of mass to orbit, but I suspect we do not have the reliability to construct this as inexpensively as the PDF's author supposes.

With the risks entailed by a catastrophic failure of this cable I certainly want a spacecraft more reliable than anything we have sitting on launchpads today to maintain this beast. I want a better answer than "duck" if Dan Rather cuts into my evening TV to announce the cable has been cut by terrorists.

I am afraid that if NASA were to bite on this idea (today) it would be one more megaproject fraught with massive cost overruns.