Space Elevator Challenge

MattSparkes writes "For the second year in a row, no team has won the $200,000 prize in the Space Elevator Challenge at the Wirefly X Prize Cup. Three teams were disqualified before the contest even started. Another competition at the event has been held up by confusion. Incredibly, it seems the organisers of the competition are not sure whether the ribbon used was 50 or 60 metres long, and whether any team completed the climb fast enough to win."

Comments

X-Prize

[bhima]

Well it seems that this will be won next year :)

More and more I see that this sort of prize is excellent way to foster development of new technologies. This should be applied to other technical challenges we face...

Re:X-Prize

[MichaelSmith]

Well it seems that this will be won next year :)

Maybe so, but I don't see anything here which will realistically form a part of a real space elevator system. Its a bit like building a railroad but starting out with model trains.

Re:X-Prize

[Anonymous Coward]

Model trains. What do you call those? Prototypes?

Re:X-Prize

[bhima]

I've been in the research & development business for pretty much my entire adult life. This, more or less, is what we do except on a different scale. I don't see anything wrong with building models of things in order to understand them more fully. Rather than attempting to solve the whole of the problem in one go they are trying to solve the parts of the problem that are solvable with today's material technology. Given a few more years doubtless the material engineering will begin to catch up and you will see things that realistically could be used in true space elevators.

Re:X-Prize

[Darkman, Walkin Dude]

Its a bit like building a railroad but starting out with model trains.

Indeed. It rather reminds me of one of those black and white 1920s films where everyone is running around at high speed, to a catchy little ditty on the piano, only I'd take it less seriously. I mean what, from the sounds of it these guys couldn't find a good time in a whorehouse, and they claim they are trying to build a space elevator?

In the words of the Jesus

Laughable, man! Haaaaa ha!!

Re:X-Prize

[Darkman, Walkin Dude]

Yes but, if you were running a competition, do you think you could remember how long the cable is?

Re:X-Prize

[lgw]

This prize addressed the climber, not the cable, so it's not entirely silly.

What I'd like to see addressed is the fundamental structural problem of stabilizing a space elevator. In getting a payload to geostationary orbit, only about half the energy required is needed for lifting. A similar amount of energy is required to accelerate the payload laterally by roughly 9000 km/h, giving it enough angular momentum to achieve a stable orbit.

A space elevator can lift a payload easily (given some advancement in materials technology), but has no real prospect of pushing sideways on a payload. As a result, conservation of angular momentum will cause the far end of the pendulum to swing. The counterweight tethered past geostationary will swing backwards in orbit, then swing forwards again as a pendulum.

The this very long pendulum will oscillate, not simply be pulled from orbit, and the amplitude won't be that high on the first payload, but every payload lifted will add energy to this pendulum - effectively all of the energy needed to accelerate the payload by 9000 kh/m. That will add up fast, and the space elevator doesn't have much prospect for damping the pendulum. The friction in the cable as it bends will shed some energy, but that's about it. It's like a car with good springs, but no shocks - it's going to bottom out eventually.

The period of a 40000 km pendulum is less than 4 hours, far shorter than the likely time for lifting the payload, so the energy of oscillation will be added somewhat chaotically as the payload ascends. It's not like to can just send of a second payload to "cancel out" the consequences of the first. You really need a strong mechanism that stops the pendulum from swinging.

Re:X-Prize

[jank1887]

Like this?:
A montage of failed flying machines from the 1920's

That flying gimmick will never take off :)

Re:X-Prize

[Rogerborg]

And what's going to drive that material technology? What, other than space elevators, requires space-elevator strength cabling? We need another Apollo project, not a bunch of interns running Lego robots up fishing twine.

Re:X-Prize

[Darkman, Walkin Dude]

That flying gimmick will never take off :)

Do you think they managed to remember what the wingspan was, down to the closest 10 meters or so? These guys should have their own sitcom, seriously.

Re:X-Prize

[rubycodez]

forget a race competition, if you were running a corporate R&D lab, what would your execs say if you did expensive robot climbing experience but "forgot" to record cable length?

Re:X-Prize

[Quaoar]

The period of a 40000 km pendulum is less than 4 hours, far shorter than the likely time for lifting the payload

Erm...even if the lifting time was 4 hours, that means the payload would have to be traveling 10,000 km/hr. I don't think it will go even a 10th as fast.

Re:X-Prize

[zippthorne]

bullet-proof vests? high performance racing sailboats? ultra-light parachutes for 747 sized aircraft?

Re:X-Prize

[bhima]

Given the sort of Manday this has been for me...

no.

Re:X-Prize

[InsaneProcessor]

Besides be an absolutely absurd concept, there is not practicality to a "space elevator". On the practical side this is laughable.

Re:X-Prize

[bhima]

Given the rate that formerly high technology materials make it in to competitive environments and then into the consumer market I don't think this is much of an issue.

Besides, an Apollo scaled project is beyond the capability of America.

Re:X-Prize

[asuffield]

What I'd like to see addressed is the fundamental structural problem of stabilizing a space elevator. In getting a payload to geostationary orbit, only about half the energy required is needed for lifting. A similar amount of energy is required to accelerate the payload laterally by roughly 9000 km/h, giving it enough angular momentum to achieve a stable orbit.

While this comes from the realm of science fiction (where did I read about this? anybody recognise it?), it's still an interesting idea:

Imagine two elevators, at opposite points on the surface of the planet. Have a ring that goes around the planet, connecting these two elevators. Let the ring be a hollow tube, inside which is a second ring which is rotating at high speed against the direction of the orbital path.

You can then arrange things so that hoisting a mass draws its lateral energy from this inner ring - so anything you hoist makes the ring slow down a little. A series of linear accelerators around the ring will adjust its speed as needed, by pumping more energy into it - but, you can also speed up the ring by grabbing some asteroids, mining them for valuable metals, and dragging the metals back down the elevator.

Such a construct is way beyond our ability to build at this time, but so is a space elevator.

Re:X-Prize

[YA_Python_dev]

The cable will probably not oscillate at all (almost) because the cars will ascend at approximatively 100 km/h, by far too slow to do anything except a very small (less than 1 degree) lean at the very bottom of the cable (remember that a lot of payloads will probably be release before reaching 10% of the total cable length).

More details on Wikipedia and googling for "Annual Space Elevator Conference" (there are several simulation for the dynamic behavior of this thing).

Re:X-Prize

[Anonymous Coward]

You do realize that you're agreeing with the post you're replying to, right?

Re:X-Prize

[twifosp]

Thats the entire point of the space elevator. There is a counterweight in geo stationary Earth orbit at the top of the cable. The cable isn't going to be very flexible, despite being called a cable. It will be very taught. As the payload goes UP the cable, lateral forces will be applied to the payload. The Earth's rotation and the counterweight in geo stationary orbit take care of this automatically.

Once the payload is released from the cable, it will need additional thrusters to move it away from the elavator, adjust it's orbital height, orbital plane, and LAN.

Re:X-Prize

[Nefarious Wheel]

I want the space elevator to look like the ones in the depths of the Planet of the Krell (Forbidden Planet, circa 1956). Lots of sparks as the enormous glassy spheres make their climb. Forget economics, let's get some drama happening.

Re:X-Prize

[Nefarious Wheel]

You really need a strong mechanism that stops the pendulum from swinging.

Vary the location of the exit point at the top from payload to payload to keep resonances from building up.

Re:X-Prize

[lgw]

One can bend quite rigid materials into 1 kilometer circles. While the cable might be rigid when compared to ordinary building materials, it will definitely flex all it needs to at a length of 40 km or so. Just saying:

The Earth's rotation and the counterweight in geo stationary orbit take care of this automatically.

... doesn't make it so. There's no cheating conservation of orbital momentum. The energy required to thrust the payload laterally will be expressed as a translational wave on the cable, all you can change is the frequency. And every payload that transits the cable will add to the amplitude, until at some point it's a problem you can't handle.

The mass of the counterweight servers to tension the cable and keep it's average position constant, but it does nothing to dampen vibration, any more than a heavier pendulum bob makes a pendulum stop swinging any sooner. Something will have to be done to change the energy of vibration into a less destructive form, as the friction involved in bending so thin a cable will be negligible.

Re:X-Prize

[lgw]

You're pretty limited in the amount of energy you can dump in this fashion. First, you have to arrange for the exit point to be an anti-node (which would make it problematic if you one day want to use the space elevator to return cargo to Earth, unless the wavelength is short). Second, the energy you can dump is limited by the frequency of the translational waves divided by the length of the cable - you only have one "wavelength's worth" of energy to work with here.

Re:X-Prize

[Iron Condor]

The counterweight tethered past geostationary will swing backwards in orbit,

More-or-less correct.

then swing forwards again as a pendulum.

No, it won't. There's no restoring force here anywhere. If you are trying to orbit any kind of "counterweight" past geosync, then the orbital period of that counterweight will be longer than one day and thus it'll start wrapping the entire tether around the planet.

To quote someone's sig around here: None of this is rocket science, really:

Write down the total force on a mass element dm in the cable. We require that the solution is stable, i.e. that none of the mass elements moves in a coordinate system that rotates with the earth. Don't forget the pseudo-forces hat are introduced through the non-inertial system.

a) for undergrads: assume the thing to be a tower (i.e. straight line, angle with ground 90 degree). Aquire a solution for the total force by integrating over dm. This will yield a quadratic expression for the required height of the tower. For the solution to be real, the expresion under the root must be positive. Verify that this is only the case if the rotational kinetic energy of the system in question exceeds the gravitational potential energy of the earth. Verify also, that this condition is not given for the earth.

b) for graduate students: Write down the continuous Lagrangian for the system. Assume, for idealisation, infinite tensile strength and unlimited elasticity of the material. Choose a proper energy Ep as generalized coordinate. Solve the Euler-lagrange equations for the problem and show that there is no bound solution for Ep if the above condition is not fulfilled.

Sorry. A space elevator is not an engineering problem because it is a physical impossibility.

(Extra credit: Compare the two energies and compute how fast the earth would have to spin to allow for such a system, i.e. for there to be a co-rotating satellite with exactly 1 day period that would actually keep the cable under tension.)

Re:X-Prize

[Eivind]

Nonsense.

Sure, the cargo needs to be accelerated eastwards, which means the top of the cable will be pressed westwards. But the cable is under stress, and the stress itself will tend to rigthen it.

It's a lot like spinning a string with a rock on the end. Sure, gravity will tend to drag the rock *downwards*, but the spin and the resulting stress on the string will tend to counteract this. End-result ? The string does go diagonally downwards somewhat, how much depending on weigth of stone, length of string, and speed of spinning. But it stays stable, and it doesn't end up vertically eventually.

The energy required for accelerating the payloads eastwards is taken from the earths rotation. So sure, if you sent up a significant part of the mass of the earth, you'd actually slow down earths rotation (and make days longer), if that *was* a problem (which it ain't for the same reason that a fly on the stern doesn't cause a supertanker to capsize) you could counteract this by sending equal masses *down* and *up* the cable.

People up. People down. Water up. Urine down. Food up. Feces down.

Or, you could, simply set up solar-powered ion-truster on the top to impart the needed momentum to the beanstalk and counteract the westwards-bending effect. It ain't gonna be nessecary, but even if it was, it'd be a rather trivial problem.

Re:X-Prize

[Eivind]

What, other than space elevators, requires space-elevator strength cabling?

It's not a question of "require" it's a question of benefit from.

Lots and lots and lots of engineering-projects would benefit from stronger, ligther cables. Any sort of tension-structure at all really. The most obvious example migth be bridges.

Yes, you can build bruidges with steel-cables. But if you had cables 10 times as strong, and 10% the weigth, you'd be able to build much longer freespan bridges, and you'd be able to save an awful lot on construction, as carrying the cables is today frequently heavier than carrying the actual part of the bridge with the cars on it.

Ask any structural engineer if stronger, ligther cables would be useful.

Re:X-Prize

[MichaelSmith]

anybody recognise it?

No, sorry. It sounds a bit like something Robert Forward would have come up with.

Re:X-Prize

[47F0]

"then swing forwards again as a pendulum."

"No, it won't. There's no restoring force here anywhere. If you are trying to orbit any kind of "counterweight" past geosync, then the orbital period of that counterweight will be longer than one day and thus it'll start wrapping the entire tether around the planet."

-----

Bizarre. mass element dm - pseudo-forces-integrating over dm - Euler-lagrange equations...

This confirms a theory I have long had that advanced math, like other dangerous weapons, should not be put into the hands of children without at least a few semesters on how to think.

Try the following thought experiment. Tie a kilogram weight on the end of a long string. Start swinging it around your head. Does the length of the string make it magically wrap around your head at some point? No. Not even if you denote some arbitrary point on the string as geo-synchronous.

Allow a ten-gram weight to slide out along your string. The assembly will deflect slightly - but your continued rotation will straighten it back out - at the expense of a little extra energy from you. To enhance the thought experiment, you are standing on a magic platform in no (micro) gravity space, swinging your string around. Can you rotate it around slowly? Yes. Can you rotate it faster? Yes. Now start slowly turning up the artificial gravity on your magic platform. Does everything wrap around your head? No. Not until the gravity is turned up to the point that the center of mass of your system falls inside the natural synchronous orbital period of your system's rotation. Then it "falls" down.

Put it another way. Speed the earths rotation up. Faster and faster, until a geosynchronous orbit is about twenty feet off the ground (It'll drive the birds nuts, but hey, it's for science). Tie a rock on a string, hang on to the end of the string and toss your rock fifty feet straight up. It'll stay up there, I promise.

Geo-synch is not really magic in terms of the system. It's simply the point at the natural orbital period equals one day, which is why the counterweight must be located past that point. Lower than that point, and of course the whole assembly falls down. But above that point, the counterweight is forced into an unnaturally fast orbit, providing tension for the assembly.

As freight moves up the cable, the cable does indeed deflect - then returns to it's natural "centripital" position - at the expense of a little rotational energy stolen from earth.

Re:X-Prize

[Iron Condor]

Bizarre. mass element dm - pseudo-forces-integrating over dm - Euler-lagrange equations...

Nothing bizarre about it. It's called "physics".

This confirms a theory I have long had that advanced math, like other dangerous weapons, should not be put into the hands of children without at least a few semesters on how to think.

I.e. people like yourself.

I gave you all the required pointers. With them, you can go and see for yourself by yourself with your own eyes that a space elevator cannot exist. But you've never learned to think, so you merely keep regurgitating the same physically impossible science fiction. Like this:

Try the following thought experiment. Tie a kilogram weight on the end of a long string. Start swinging it around your head.

It is physically impossible to swing a mass around my head unless I rotate it fast enough. Do yourself and me and all the readers a favor and do not respond to the previous sentence until you have learned to think.

The correct thought experiment here is a flat, slippery table, the kilogram sliding frictionless on the table, you are in the center of the table (sticking out through a hole, say) and you're trying to orbit the mass around you on a rope. If you are going fast enough, this will obviously be possible. But if you're going very, very slowly, you're merely going to wind the rope around you, reeling the weight in towards you.

The earth rotates once per day. Which is too slow. As you could see for yourself if you were willing to do the math.

Once you start thinking, you realize that the total rotational kinetic energy of the system must exceed the gravitational potential for the apparent force on the object (in the rotational coordinate system) to be directed outward. No, that's not going to be revealed to you by some kind of magic, it requires that you learn to think.

To enhance the thought experiment, you are standing on a magic platform in no (micro) gravity space, swinging your string around. Can you rotate it around slowly? Yes.

No, you cannot. If you rotate slowly enough you simply become a spool upon which the tether winds itself until the mass has been reeled in.

Put it another way. Speed the earths rotation up. Faster and faster, until a geosynchronous orbit is about twenty feet off the ground (It'll drive the birds nuts, but hey, it's for science). Tie a rock on a string, hang on to the end of the string and toss your rock fifty feet straight up. It'll stay up there, I promise.

Of course. Which is what I have been telling you all along: if the rotational energy of the system is high enough, then a space elevator tied to a geosync station is possible. In the case of the Earth, it is not high enough. That is all there is to it.

Geo-synch is not really magic in terms of the system.

So why are you treating it as if it were magic? As if the invocation of "geosync" alone absolved you from the necessity to do your homework, compute all the forces and energies in the system and see for yourself what's going to happen?

Your unwillingness to examine the actual, real, true (capital R) Reality of the situation in favor of hand-waving and invocation of magic makes it quite clear where you're coming from.

Re:X-Prize

[lgw]

The earth rotates once per day. Which is too slow. As you could see for yourself if you were willing to do the math.

Geostationary is exactly the radius at which the speed of rotation is "just right" - clearly, as it's a stable orbit. Inside geostationary with a rotation of once per day is too slow, which makes standing on the plant's surface stable. Outside geostationary with a rotation of once per day is faster than the stable circular orbit, so stability is achieved when the cable applies enough centripetal force to pull the weight around that fast. Going faster than stable orbit requires tension on a cable to hold the weight in place.

I think you flipped a sign somewhere.

Re:X-Prize

[lgw]

Sure, the cargo needs to be accelerated eastwards, which means the top of the cable will be pressed westwards. But the cable is under stress, and the stress itself will tend to rigthen it.

If you have a mass at the end of a pendulum, and press it westwards 1 foot, and release it, the cable is under stress from the force of gravity acting on that mass, and that force of gravity added to the stress on the cable will tend to righten it. The mass will swing eastwards 2 feet, then westwards 2 feet, ocsillating forever unless we introduce friction to dampen the wave.

The orbital mechanics which combine with the stress on the cable tethering a counterweight past geostationary orbit works much the same way. The counterweight once displaced to the west will sure enough return to "center", but just like a pendulum it will have kinetic energy when it gets there equal to the total energy used to displace it in the first place, and it will continue moving east to the same angle "off-center" (assuming small angles here), then swing back past "center" to the initial displaced position, swinging back and forth forever unless some force is introduced to dampen the wave.

Unfortunately for your ion-thruster idea, the extreme tension on the cable will cause it to act more like a guitar string than a pendulum, and you'd likely get standing waves at every harmonic. Actually, it would be more of a mess than that, as the payload moving up the cable will first create a series of waves moving along the cable, which best case stabilize as standing waves. Of course, thrusters all along the length of the cable would work fine, but aren't very practical unless they're very light indeed.

Adding tension to a cable does very little to dampen energy expressed as waves on that cable: all it does is increase the frequency of those waves (which does increase the effect of the friction of bending the cable, but that friction is very small on this scale).

Re:X-Prize

[Eivind]

There's a number of reasons things don't work out like that.

First, there actually *is* friction. So it's obvious the elevator would not swing forever. Second, you claimed that each cargo sent up would tend to strengthen the swinging, until something breaks. That's also not true. That *would* be true if the cargo was sent up and released at the worst possible moment.

In the best case, two following cargoes cancel exactly. Like this:

First cargo goes up, presses top eastwards, whereafter the top swings westwards to neutral, and *would* overshoot to go an (almost) equal distance westward. Except you send up cargo 2 with such timing that it's eastward pressure cancels the westwards motion of the elevator, so that at the moment you release cargo 2, the elevator is both vertical, and at rest.

In practice, there's likely to be many cargoes on the way up at any given time, this acts a lot more like a *constant* eastwards pressure. (in the limit, infinitely many infinitely small cargoes, it *would* be a constant pressure)

You *do* need to take care that you don't put energy *into* the standing waves that will inevitably build quicker than the energy dissipates. That can be taken care of in two ways (or a combination thereof).

Put less energy in. (by timing, by size of cargo, by equal-symetrical-shipping whatever)

Or make the energy dissipate faster, by passive means (increase friction, dampeners) or active means (ion-trusters at top , or movement of the bottom-point that actively work against the waves, for example)

Re:X-Prize

[Urkki]

a) for undergrads: assume the thing to be a tower (i.e. straight line, angle with ground 90 degree). Aquire a solution for the total force by integrating over dm.

Surely you are aware that a space elevator is not a tower? It's a satellite on geosynchronous orbit, which just happens to reach all the way down to Earth (or at least almost, close enough that you can build a tower to reach the lowest end of the satellite so you can grab it.

If you believe that it's a physical impossibility, then can you please tell me, what is maximum length of a vertically (perpendicular to Earth surface some 36000km below) oriented piece of cable, with centre of gravity at GEO?

If you can't be bothered to calculate, could you at least give me a top-of-your-head ballpark estimate from these:

1m?
100m?
1km?
100km
10000km?
2x36000km?

Climbing the cable is then a different matter, and there's no point in going into that before we establish that a space elevater shaped satellite on GEO is not physically impossible.

Re:X-Prize

[47F0]

"Nothing bizarre about it. It's called "physics"."

Actually, it's called mis-applied physics.

Point 1)

My math (Ok, I borrowed it from a guy named Newton) says that satellites can orbit. Even in geosynchronous orbit. Apparently they can - they're up there today. As is the moon, the earth, etc. Hopefully, we can agree on that. It is necessary for all that follows. (And also to keep the universe from flying apart)

And, as I stated, geosynchronous orbit, is in fact, absolutely not magic - the only magic about geosynchronous orbit in this application is that it is the one orbit that allows an orbital body to remain static over the earth's surface - it has no other magic in the behavior of tethered, or asymetric orbital systems. For a space elevator, it is undesirable to have your ground terminus dragging across the ground. But the particular orbital altitude really has zero relevance to the behavior of asymetric systems in orbit.

If the earth rotated faster, or slower, the orbital mechanics would remain unchanged - they rely purely on gravity and inertia and are oblivious (aside from minor frame-dragging effects in the fabric of space) to the rotation of the body beneath them.

So for the sake of the physics, the orbit absolutely does not matter - it may be eighty miles up, or eighty-thousand miles up - we are only considering the behavior of any asymetric system in any circular orbit - once you've got a handle on that, geosynch is simply a desirable orbit to allow a fixed relationship to a rotating body.

Point 2)

Assuming this radical leap, that object can in fact orbit, can we also agree that each orbit has it's own period, i.e. velocity, and that an object that is moving too slowly for it's orbit will move inward and an object moving too rapidly for it's orbit will move outward?

I hope so, because if not, we're going to have an awfully tough time from here out figuring out where our satellites go.

Given that, the math also says you can extend a couple of weighted, tethered strings from a body in orbit - one directed inward and one outward. The inward tether will "fall" towards the earth - the outward tether will pull away. Why? Because the center of mass of the system remains in it's original orbit - honest - it has to. The inner tether is moving too slowly for it's orbit - and pulls inward - it's velocity is insufficient for it's orbit.

That's Newton 101. The center of mass of the whole system remains precisely in the same orbit - at precisely the same velocity.

The inner tethered mass cannot accelerate the whole assembly - that silly conservation of energy thing - it can't speed up (it's tethered,remember?) so it continuously falls. The outer tether is moving too rapidly for it's orbit - similarly, it cannot decelerate the entire system - and pulls outward. Or do you also revoke Newton?

Your denial of this fact suggests that tidal alignment is not a factor in orbital mechanics - yet it is. Or perhaps it's just an amazing coincidence that the moon's rotational and orbital periods are identical?

Point 3)

If you grant that, Point 1, bodies can, and do, orbit, and Point 2, that any mass-point moving too slowly for it's orbit moves to a lower orbit, and any mass-point moving too rapidly for it's orbit moves to a higher orbit, then where is the inconsistency? All that is necessary from those points to derive a (theoretical) space elevator is to select an orbit that matches the rotational period of the body beneath it (the "magic" geosynchronous orbit) and extend the orbiting tethers such that the inner tether can reach the ground.

I admire your ability not to let reality interfere with your equations - but your equations may not be the right wrench to hammer that nail in.

Re:X-Prize

[Rogerborg]

And these stronger, lighter cables of which you speak; is it necessary to have cables that are sufficient to build a space elevator?

99% of the way there doesn't cut it. Someone, somewhere will have to fund the development of materials for a beanstalk. Who's that going to be?

Re:X-Prize

[Anonymous Coward]

adjust it's orbital height

"its".

Re:X-Prize

[Anonymous Coward]

keep it's average position constant

"its".

Re:X-Prize

[Anonymous Coward]

with such timing that it's eastward pressure

"its".

Re:X-Prize

[Anonymous Coward]

then returns to it's natural "centripital" position

"its".

Re:X-Prize

[Anonymous Coward]

each orbit has it's own period
too slowly for it's orbit
too rapidly for it's orbit
remains in it's original orbit
too slowly for it's orbit
it's velocity is insufficient
for it's orbit
too rapidly for it's orbit
too slowly for it's orbit
too rapidly for it's orbit

"its".

the right wrench to hammer that nail in

"the right wrench in which to hammer that nail".

Re:X-Prize

[Eivind]

I don't quite get your question. What exactly do you mean by "necessary" ? Having a space-elevator (or indeed a space-program at all) is not "necessary" for suitable definitions of that word.

Regardless of how strong/ligth cables you have, there's always going to be an advantage to having a yet-stronger yet-ligther cable. The advantages are diminishing offcourse, going from rope to steel-wire has a larger benefit than from steel-wire to carbon-nanotube-rope. But both are there.

Your assertion that "99% of the way doesn't cut it" is also nonsensical. Actually, in theory *any* material with tensile strength can be used for a space-elevator. It's just that without a high strength/weigth ratio the needed tapering would be ridicolous. If you made one of normal steel for example, the "cable" would, at geosynch orbit be several miles thick. Which makes it unworkable in the real world.

With a cable with half the strength of a single CNT, you could get to geosynch orbit without tapering at all. If the cable was only 99% strong enough to do that, the consequence would be you'd need sligth tapering. Big deal. You make it out as if there's some hard limit. There ain't. There are just soft limits. (i.e. weaker means more tapering, so at *some* point you're in "impractical" territory, but it's not a case of black and white like you seem to believe)

Re:How could you do this now?

[PieSquared]

The structure of the elevator isn't the only technology that has to be developed. We also have to make a climber that can go up a thin strand of material and hold wait, as well as a way to power it. Not all of these require carbon nanotube robes to build.

Ribbon

[MattSparkes]

I think that the material to make the ribbon can't actually be produced yet, and a 50-60 metre long section is about all that can be used. However, for the purposes of a test like this, it will suffice. The competition is more to do with getting the elevator technology advancing than actually putting together a working device.

Re:Ribbon

[Rogerborg]

But how does this help? $200,000 is chump change. It's not enough to pay the guy who runs the accounts of a serious research project. That number needs another three zeroes on the end before it will actually produce anything new.

As the article says, none of the teams actually created their own materials, they bought off the shelf. That's like trying to push forward hybrid car technology by awarding a prize to the team that brings the cleanest Prius.

Re:Ribbon

[KillerBob]

You're right. it is chump change. Do you know how much was spent developping SpaceShipOne? Or the other entries? My guess is that $10 million doesn't begin to cover the amount of capital spent on development....

It's not the money that makes them do it. It's the competition. The notion that other people are competing for the same prize awakens something primal in human nature, and drives us to the goal. $200k isn't much money, but it's enough to get the attention of the people competing.

Re:Ribbon

[Defes'an]

Having actually been to the competition, I can correct a few things. The ribbon was NOT made out of carbon nanotubes. The creation of the ribbon material is, in fact, an entirely different contest. The ribbon was actually plain old rubber. The costs for each climber ranged from $2,000 to $50,000. $200,000 is actually pretty good for these people. SpaceShipOne was funded to the tune of twenty million dollars, as far as I know. Ten million wasn't enough to cover the costs, but it went a good way. Finally, last year, the top climber didn't even get to the top of the ribbon. This year, the top climber did it in two minutes. I'd say a win is quite likely next year.

Re:How could you do this now?

[kyknos.org]

RTFA. You do not need to climb to orbit to win the prize. "a test of over 20 teams to use light to power a vehicle along a tether, this year up about 50 meters..."

Re:How could you do this now?

[Smidge204]

The competition was for building a vehicle to climb the ribbon, not making the ribbon itself.

There is a seperate competition for designing/making the actual ribbon.

Ref: http://www.elevator2010.org/site/competition.html

=Smidge=

X-Prize Foundation

[Raynor]

is already responsible for a major advancement: the first private space ship able to relaunch in two weeks (SpaceShipOne).

The prize is definately motivation, and the X-Prize foundation has a few contests going:
-The Ansari X-Prize (Get 3 people to 100km twice in two weeks) - WON
-The Archon X-Prize (Sequence 100 people in 10 days with $10,000 cost per person) - OPEN
-The Automotive X-Prize (Currently being developed. Create super-efficent cars or alternative energy) - FUTURE

Those are the three the X-Prize Foundation has created. An interesting fact from the X-Prize website: "Ten times the amount of the prize purse was spent by the competitors trying to win the prize."

Re:X-Prize Foundation

[Shadowmist]

Important thing to remember, SpaceShipOne did not acheive anything near orbital velocity. In fact I'm not even sure it was close to the velocity of Alan Shepard's suborbital Mercury flight. Hence it did not have to deal with severe re-entry heating, so was spared one of the critical neccessities of the Space Shuttle. I'm not knocking the acheivement of this group, just putting it in perspective.

Re:X-Prize Foundation

[LordVader717]

I wouldn't give it that much credit. One achievement, which was long overdue, and not all that intersting (when will we get people to orbit?). It might have made the project a bit more exciting, but giving the credit to the prize is a bit of a long shot, not least because the development costs far outnumber the prize.

What it is good for though, is setting actual real-world goals for scientists to achieve, learn from, with the prospect of winning the prize and the fame. They compete with other entries and it also sparks interest in it, rather than only staying a concept, with no specific development.

Re:X-Prize Foundation

[Darkman, Walkin Dude]

I'm not knocking the acheivement of this group, just putting it in perspective.

At least they managed to get higher than 50 meters. Or was it 60? Haaaaaaahahaaa, tragic...

Re:How could you do this now?

[Anonymous Coward]

To be fair, it doesn't matter much if they have funding to make the tether, since the tech to do this isn't even possible at the moment. A lot of people get stuck on carbon nanotubes and think that a space elevator is coming tomorrow, but when you look at current research we aren't really up to making a long fiber out of nanotubes (and when/if we get there, there are heat properties that I always wonder about in a space elevator, for instance a photo flash is enough heat to ignite loose nanotubes). The contest is really meant to develop that sort of tech.

That being said, yeah small teams would have a hard time with it. though they didn't say who was funding the disqualified teams, they did say the team that tested was part of an aerospace company.

Dupe dupey dupe dupe

[Novotny]

I preferred the 'Canadians Vie for Space Elevator Victory' title this piece was given further down the page.

Re:Dupe dupey dupe dupe

[Raynor]

Actually this is a half dupe, since the main contest here is the fiber strength not the elevator. It is a secondary note.

Sounds like IT

[Gothmolly]

Infosec: "We don't really know what you're doing, but we're certain it's bad. Disqualified!"
Development: "We're not sure how long the cable is supposed to be, so we'll hardcode it in the top of the code. If we're wrong, its out of scope and we won't fix it."
Engineering: "We don't know how fast it is supposed to climb, so we'll pick a value. If we're wrong, it was Marketing's failure to gather the right requirements.""
Audit: "All your project are belong to us".
Milton: "I could just burn down the building..."

Geez, who is running this thing, the PHB?

Re:Sounds like IT

[TubeSteak]

Geez, who is running this thing, the PHB?

Even better, it's being run by the lowest bidder(s).
/rimshot

Re:How do they work?

[MichaelSmith]

How does a space elevator work?

If you attach a weight to a rope and spin it around your head the inertia of the weight will keep the rope tight. Because the Earth rotates, a large mass a long way out in space should be able to keep a line tight. The bottom end would be attached to the Earth, preferabley close to the equator. A station close to Geosynchronous orbit will be in microgravity. The weight at the end of the cable will experience rotational pseudo gravity. Objects dropped from this point will enter solar orbit.

Call me picky but..

[clickclickdrone]

If I'm going up in to space on a giant elevator, I want it to be nailed on to something a bit more substantial sounding that a 'ribbon'. Heck, all the ones I used to read about in 1950's sci-fi books were basically normal elevators, steel girders, nice big box with windows, sliding doors etc., just a hundred thousand feet high. THAT's what I'd feel safe in.

Re:Call me picky but..

[Shadowmist]

No such structure could withstand the tensile stress generated from being pulled at opposite ends 25,000 miles apart. Just to put some perspective here, a the length of a space elevator, depending on which source you quote is at the minimum over 3 times the diameter of the Earth itself!

Re:Call me picky but..

[aadvancedGIR]

Don't worry, you're far more likely to die in a failure of your home/office elevator than in a space elevator.

Re:Call me picky but..

[mattdm]

Hence the challenge. Clearly, current materials can't do it. Sci-fi implementations usually involve some sort of nanotech manufacturing.

Re:Call me picky but..

[clickclickdrone]

I didn't actually think it could be built, it was an attempt at humour.

Re:Call me picky but..

[Shadowmist]

Nanotech as it's most commonly used in sci-fi is kind of like warp drive in Star Trek, a magical invocation used to create shortcuts in story plotting but not particurlarly meaningful beyond that.

Re:Call me picky but..

[mattdm]

Yep. It's not clear that it's really possible. However, unlike warp drive, it's at least not violating the laws of physics.

Re:Call me picky but..

[Flentil]

Because our current materials aren't strong enough, so they're working to make stronger materials. But then why, when they have these nanotube woven ribbons, would they stop at a ribbon? Why not use these super materials to build s super structure instead of trying to dangle a ton from a super strong hair? Why not weave those ribbons into thick cords or girder-like hard materials to build something real?

Re:Call me picky but..

[Iron Condor]

However, unlike warp drive, it's at least not violating the laws of physics.

Yes, it is very much violating the laws of physics.

Of course I cannot force you to open a mechanics book. That would be up to your motivation.

Re:Call me picky but..

[Shadowmist]

You don't use girders for the same reason that the largest bridges are suspension bridges. You need the flexibility to deal with stress, even with something that's a geo-synch cable, there will be variations in force. The other thing is that you need something with the impossible combination of being comparatively light and strong and girder construction simply doesn't cut it.

Re:How do they work?

[Shadowmist]

In theory it works well. In practise I think it's more of a pipe dream and I believe NASA knows it. We have one football field sized structure that's taken the better part of a decade to build. We've never constructed something anywhere near the magnitude for the size this thing is going to be and as far as I know there isn't a good engineering plan on how this thing is supposed to be put up. However they're desperate for whatever good will and publicity that they can scramble to get and this competition even with all it's strings attached is a pretty good and inexpensive way to generate some.

Re:How do they work?

[Anonymous Coward]

Go to university and take physics 101.

lots of competitiors, drama, technology.

[heitikender]

And not ONE picture or movie about it? How come?

Pretty picky

[Dan East]

According to the rules, the circumference of the loop must measure at least 2 metres. ...the Snowstar team from Canada's University of British Columbia, for example, was shy of this by less than half a millimetre.

The diameter of their spool was 0.25% smaller than required, which was probably the result of warping from moving the spool around so it could be weighed, etc, before the competition. So they were disqualified and didn't get to formally compete.

The height of the robot climb is what got me. It's a timed event, and the height they had to climb might have been 10 meters further than the benchmark. Now that's a complete joke.

Dan East

Re:Pretty picky

[AGMW]

The height of the robot climb is what got me. It's a timed event, and the height they had to climb might have been 10 meters further than the benchmark.

... and why couldn't they measure the stupid thing after the event? They really need to sort themselves out if they want people to come and play next time. And the 2 metre loop - they have to tell the competitors how it will be measured - maybe have a "measuring machine" that competitors can have access too. The competitors must load their own loop onto the machine to be measured too, so they can't cry foul thinking it was measured wrong.

It really has to all be above board with no room for arguments or people will get fed up!

Re:Pretty picky

[Cr33pybusguy]

Leave it to engineers to screw up something so damn simple. I can fix your length query in about ten minutes with some really sophisticated technology. It's tricky to use but after about thirty years daily use you can get pretty good at using it. Wait for it..... IT'S A TAPE MEASURE!! TADA!!!! Am I the only one who thought of this revolution in measuring technology?

Re:Pretty picky

[Penty]

It wasn't a climb X number of feet event. It was a climb at least 1m/s event. They were slow by a couple of seconds.

Re:How do they work?

[Maddog Batty]

Just Google it

Its not all that difficult...

My plan!

[BeeBeard]

You know how people sometimes use the metric of "If you stacked all the X in the world (graham crackers, AOL CD's, empty pantyhose containers) end to end, it would reach the moon and back!" My tentative plan is to find those items and to dedicate them to that exact purpose. Mole of Twinkies stacked end to end, here I come!

Re:How do they work?

[KlaymenDK]

I can't imagine you don't know how a space elevator works AND don't know how to find out ... in any case, I'll presume you aren't trolling.

See http://en.wikipedia.org/wiki/Space_Elevator, or for that matter Arthur Clarke's "The Fountains of Paradise".

The clue is that an elevator is attached to a *GEOSYNCHRONOUS* satellite. That is, it will stay at the same place above the Earth's equator. Granted, there would probably be some amount of drift, but that can probably be solved by applying steering thrusters to the whole contraption.

So you have to go to the place where the elevator is; but once you're there you can just use it as any ol' elevator.

Re:How do they work?

[ravenshrike]

Ding. The footprint for a truly sturdy space elevator would probably be around the size in square mileage of Delaware, if not greater.

Other end?

[ThePhilips]

Can anyone enlighten me how that thing supposed to work?

We fasten one end on ground and second end is fastened... where???

And what about Earth rotation?

[sarcasm] Which TV show the people pursuing that idea watched too much? [/sarcasm] I cannot recall a show which had advertised that idea. I still think that normal elevator - a-la tower - is much saner idea and can be achieved easier, since it doesn't depend on another end. I think it is more feasible idea compared to super strong tether. Though I was already flamed twice on /. for such opinions. Apparently the TV show was too good.

Re:Other end?

[Anonymous Coward]

Can anyone enlighten me how that thing supposed to work?

See Wikipedia.

We fasten one end on ground and second end is fastened... where???

To an orbiting counterweight.

And what about Earth rotation?

Earth's rotation is what makes it work. Otherwise:

I still think that normal elevator - a-la tower - is much saner idea and can be achieved easier

Yeah, nobody ever thought of that idea. They're pursuing orbital tethers because they're all insane masochists.

A tower would be much more massive and would have to support its full weight. Tethering to an orbiting counterweight allows centrifugal effects to lighten the total load, since the Earth is rotating. You couldn't build one high enough to reach geosynchronous orbit, and thus whatever you brought to the top wouldn't be in a nice circular orbit when it got there; it would still need something like rocket thrust. With a tether, as soon as you get up to geosynchronous, you're automatically in a circular orbit. See the "compressive structure" entry on Wikipedia.

Re:Other end?

[gclef]

For some intro info about the space elevator, try starting at the wikipedia entry on it. In short, if the cable is long enough, with the proper counterweight, the center of gravity of the cable + counterweight will be at geostationary orbit. So it won't be attached to *anything* at *either* end. It'll just hang there, in sync with the earth's rotation. We'll then attach climbers to it & use it like a big pole that we'll climb to orbit, rather than using rockets.

A straight tower couldn't be built. The tensile pressures on the building would be insane. Heck, we can't even make the ribbon yet, and it's an easier task (though still not exactly easy) than trying to build full-on girders.

Re:Other end?

[ThePhilips]

A tower would be much more massive and would have to support its full weight.

Precisely my question. So you are saying that tether might be possible to be made so light and strong - but no way simple tower construct would achieve the same???

If you can make tether that strong and light, you can use N of them to make tower stand. Materials for such tower also can be very very light and very very hard. But probably to not such greater extent tether has to be strong.

What makes super-super-strong tether in your mind possible and super-hard and super-light tower impossible?

... an orbiting counterweight.

But how heavy it would have to have? I shiver to even think that thing might alter (or even de-orbit) Earth. The wikipedia page doesn't answer that question.

It kind'a reminds me of other problem, since again we forget about balance.

Re:Other end?

[Itanshi]

bubblegum crisis 2040 has a neat space elevator

gunnm (battle angel, manga specifically) as well, this one uses the premise of geosynchronous orbit

Re:Other end?

[aug24]

Not too sure if you are joking, but I'll bite:

We probably could build a tower from known materials (eg stone which is really, really, hard to crush, hence cathedrals etc). However, a tower is not stable. It would fall over at that height, even with our current best engineering efforts. Unless you made it very wide. Very, very wide, as it needs to be at least 50 miles (70 would be better) high to be useful. Our current tallest buildings are less than 600m high (that's less than 1% of 50 miles).

The other end of the ribbon is fastened to an counterweight asteroid a long, long way out, in geo-synchronous orbit. This means that it would be a stable structure requiring no special real-time balancing act. The (forst) problem is that we don't have a material with sufficient tensile strength.

We are currently believed to be more likely to solve the problems in (2) than (1). We may be wrong!

Justin.

Re:Other end?

[at_18]

But how heavy it would have to have? I shiver to even think that thing might alter (or even de-orbit) Earth. The wikipedia page doesn't answer that question.

Do a couple of calculations. The ribbon is a fraction of mm thick and from some mm to maybe one meter wide, and 40,000 km long. Its mass is very small, some thousands of tonnes probably. That's insignificant with respect to Earth's mass.

A tower, on another hand, would be *much* more massive, not to mention impossible to build with any known, or foreseeable, material.

Re:Other end?

[ThePhilips]

IOW, the tether would manage to: (1) be very light, (2) be strong enough to sustain centrifugal energy of counter weight, (3) be even more stronger to carry useful load.

Just how this more feasible that ribbon is a fraction of mm thick and from some mm to maybe one meter wide would manage that?

A tower, on another hand, would be much more massive, not to mention impossible to build with any known, or foreseeable, material.

Your post suggest that material for tether/ribbon is already known. So why we held that competition then? ;-)

The materials are not known. And it is kind of gamble to know which material would be invented first: one to make the tether or one to make a tower.

Tower doesn't have to be all that tall. It must be high enough to fraction Earth gravity force by e.g. ten - requiring ten times less of fuel to launch elevated rocket. That would already be achievement. With "space elevator" - no such gradual progress seems to be possible.

Re:Other end?

[eggstasy]

Ok I am not a physicist or civil engineer or anything... but it seems to me that you can't make a building out of rope ;)
Some materials are engineered for compression, such as the hollow bricks you so often see, and other materials are engineered for tension... a rope can't hold itself upright, it will fall down and fold, and if you try stretching a brick you will simply break a piece off of its edge.
Go play some Pontifex or Armadillo Run... it makes this sort of physics a tad more intuitive :)

Re:Other end?

[Anonymous Coward]

So you are saying that tether might be possible to be made so light and strong - but no way simple tower construct would achieve the same??

Yes. The tether is kept under tension, rather than compression. Different material properties in question. As I said, a tether with an orbiting counterweight has to support less of its own weight than a compressional tower does, due to the centrifugal force.

While a material with appropriate tensional properties for a tether is hard to achieve, a material with appropriate compressional properties for a tower is even harder to achieve.

But how heavy it would have to have?

That depends on the design. Some designs have counterweights on the order of 100-1000 tons.

I shiver to even think that thing might alter (or even de-orbit) Earth.

It's in high orbit (above geosynchronous). It can't just "deorbit" and fall on us; there isn't any atmospheric friction to speak of. It would require enormous energy to alter its orbit to intersect the Earth. You might as well worry about the Moon falling on us.

It kind'a reminds me of other problem, since again we forget about balance.

What the hell are you talking about?

Re:Other end?

[Anonymous Coward]

Tower doesn't have to be all that tall. It must be high enough to fraction Earth gravity force by e.g. ten - requiring ten times less of fuel to launch elevated rocket.

Reducing the force of Earth's gravity by 10 doesn't equate to 10x less fuel. The fuel required is a function of the change in velocity needed; it's more related to reducing energy than reducing force (1/r vs. 1/r^2). See the rocket equation.

Anyway, the altitude required to reduce the force of Earth's gravity by 10 would be almost 14,000 km above the Earth. And you still wouldn't have the right velocity for orbital insertion.

With "space elevator" - no such gradual progress seems to be possible.

Orbital tethers don't have to be geosynchronous. See tether propulsion. Besides, if you crunch the numbers, you will find that a compression tower has to be quite high before any substantial benefit in fuel reduction is achieved.

Re:Other end?

[Control Group]

If you can make tether that strong and light, you can use N of them to make tower stand. Materials for such tower also can be very very light and very very hard. But probably to not such greater extent tether has to be strong.

What makes super-super-strong tether in your mind possible and super-hard and super-light tower impossible?

Well, for one thing, tensile strength and compressive strength aren't the same thing. A substance which would withstand the pulling force of a fixed space elevator (from earth's surface through GSO to a counterweight) would not necessarily be able to withstand the compressive force of supporting its own weight.

Then there's the balance issue. If you build a tether with its center of mass at GSO, it's in free orbit around the planet. This means it has zero chance of falling over, whereas a shorter tower's center of mass would need to always be over its surface footprint. The higher you make the tower, obviously, the harder this is to maintain.

If you can make tether that strong and light, you can use N of them to make tower stand. Materials for such tower also can be very very light and very very hard. But probably to not such greater extent tether has to be strong.

This is simply untrue. If I'm standing on top of a building and lower a rope to the ground, someone can climb it. This doesn't mean you can build a tower of that height out of the same material (a rope). (In this analogy, the top of the building is the counterweight on the end of the tether, which holds it taut)

But how heavy it would have to have? I shiver to even think that thing might alter (or even de-orbit) Earth. The wikipedia page doesn't answer that question.

It doesn't answer this question for the same reason it doesn't answer the question of whether the Klingons will think that the tether is a threat to them, and therefore attack the human race: it's a complete non-issue. For one thing, the earth gets heavier every day, as crap from space falls into it (from dust all the way up to visible meteors), probably more in a year than the mass of the asteroid counterweight. I'm not worried about de-orbiting the planet anytime soon, are you?

If you're really worried about it, let's make the counterweight out of material taken from the planet, thereby not changing the planet's mass at all, and therefore not affecting its orbit around the sun.

I don't think you grasp how much mass and velocity the planet has.

Re:Other end?

[VWJedi]

I shiver to even think that thing might alter (or even de-orbit) Earth.

It's in high orbit (above geosynchronous). It can't just "deorbit" and fall on us; there isn't any atmospheric friction to speak of. It would require enormous energy to alter its orbit to intersect the Earth. You might as well worry about the Moon falling on us.

I'm not certain what the original poster meant by this sentence, but I took it to mean that the space elevator and counterweight would affect earth's orbit around the sun. I doubt that the mass would be enough to make a significant difference, but it would certainly change earth's center of gravity to some degree.

Along this same line of thought, this could have an effect on tidal patterns as well. (The part of earth near the elevator might experience a "permanent high tide".)

Re:Other end?

[Control Group]

OK - let's shoot for reducing acceleration from gravity from 9.8N to .98N, as you suggest.

Gravity falls off according to the inverse-square law. So, to achieve 1/10 the force of gravity, you need to get sqrt(10) times as far away from the center of gravity of the planet. So we have to get just over 3.1 times as far from the center of gravity as we currently are.

So, how far from the surface is that? Let's assume that the planet is a perfect sphere of uniform density, which will make the center of gravity (conveniently) co-located with the center of the planet. According to Google, the radius of the earth is 6,378.1 km, but we're using two sig figs for the multiplication, so we'll call it 6,300 km. Obviously, three times that is 19,000 km. Subtract the 6,300 km we're already at, and we're at 12,000 km.

Now, explaing to me again how it's so much more feasible to build a tower 12,000 km tall than it is to build the tether with a counterweight?

Re:Other end?

[Anonymous Coward]

The presence of a 1000-ton mass beyond geosynchronous orbit will have an utterly, utterly negligible effect on the Earth's center of gravity or on tidal forces.

Take tidal forces, for instance. The distance geosynch orbit is about 40,000 km (I'm rounding up to 1 sig fig); the radius of the Moon's orbit is about 400,000 km. Since the counterweight is 10x closer to the Earth than to the Moon, that increases its tidal strength by the cube root of 10, or about a factor of 2. However, that is offset by a 10^20 reduction in mass. So the tidal forces due to the counterweight would be almost a billion trillion times weaker than those of the Moon.

The counterweight used in many space elevator designs is not that much more massive than the International Space Station. That certainly doesn't produce significant gravitational effects, despite being in low Earth orbit instead of geosynch. Hell, even a typical-size asteroid in low Earth orbit wouldn't produce significant gravitational effects at the Earth's surface.

Re:Other end?

[WalksOnDirt]

Since the counterweight is 10x closer to the Earth than to the Moon, that increases its tidal strength by the cube root of 10...

No, it's the cube of 10 i.e. 1000. This is still, of course, completely insignificant.

Re:Other end?

[Anonymous Coward]

D'oh. You're right, of course.

Re:Other end?

[Big_Breaker]

A big base also means a immobile base. The most considered plan for a space elevator has it anchored to a platform at sea. That allows it to move out of the way of storms and other localized issues.

That brings up an intersting idea though - your tower could float at sea. Every 100 meters of tower decreases the material constraints on the ribbon - though not by that much.

Personally I think a space elevator on earth is a bad idea. The material constraints are too close to the scientific limit of carbon nanotubes. We should build an orbital ferry with a tether that drops down to the edge of the atmosphere to grab more conventionally lifted payloads. This is sometimes called a sky hook.

The orbital ferry would have it's orbit recharged by also catching carefully timed high velocity dead mass. The recharging mass would come from earth (or moon) based accelerators. In a charged state the ferry has a highly elliptical orbit that still brings it in, very close to the earth. The discharged state is a simple LEO orbit.

Re:How do they work?

[evilsofa]

You start at geosynchronous orbit over the equator. You spin your cable both down towards earth and up into space at the same time, which balances the cable.

Re:Didn't measure the tether first?!

[PIPBoy3000]

Actually, they did, but in classic NASA fashion, they couldn't remember if they did it in metric or not.

Pixel and Texel design constraints

[rbanffy]

I don't know if anyone noticed that, but the Pixel vehicle seems somewhat unstable with its single engine.

You can see it here http://media.armadilloaerospace.com/2006_09_23/Pix elQualification.wmv, later in the hover, when it starts to oscilate the engine thrust vector in order to stabilize the craft. The oscilation seems to be increasing, but it's hard to tell since the hover itself is too short.

I know they _are_ rocket scientists and, no doubt, know about this. But it seems to be a major obstacle to achieve the 180-second hover goal.

I wonder what can be done to improve it without compromising the single-engine simplicity.

Re:Pixel and Texel design constraints

[BigBuckHunter]

Bigger Gyro?

Re:Pixel and Texel design constraints

[qbwiz]

They might be able to decrease the reaction time, which would make the reactions smoother. Also, they can change the 4 little side engines from either being on or off, to being able to throttle different amounts.

Re:Pixel and Texel design constraints

[Anonymous Coward]

The second paragraph below the movie on their website.

We didn't realize it until I looked at the side view video and telemetry back at the shop, but all the problem turned out to be was that the vehicle position drifted enough that it was tugging on the tether bungee cords, which caused lots of firing of the lox side roll thrusters, depleting a lot of lox ullage pressure, and also caused the oscillations. If we had been flying without tethers, we wouldn't have seen either issue.

Re:Pixel and Texel design constraints

[mozzis]

I was at the X-Prize event and saw Pixel (and Texel) fly. Whatever the previous instabilities were, at the event this weekend the craft flew really well. The main problem was that they could not see the landing pad because of the dust being stirred up by the engines (welcome to New Mexico!) and so landed partly off the pad. But the horizontal part of the flight looked rock-solid.

Re:Pixel and Texel design constraints

[rbanffy]

Sorry. I got the video from a news site. They didn't carry the text of the page

Re:Pixel and Texel design constraints

[rbanffy]

Nice to know. I'll try to find a video of that flight.

Intro to Space Elevators

[thelordx]

For those who don't have a good understanding of Space Elevators other than some Sci-Fi you may have read that was written 50 years ago: A space elevator consists of 5 primary components: 1. Base Station 2. Ribbon 3. Climber 4. Counterweight 5. Power system This contest is an attempt to trigger innovation in the area of power and climber, not in the ribbon, station or counter-weight. The ribbon would need to be a carbon nanotube-based composite that is a matter of microns thick and very wide. The width of the ribbon would change based on whether it is in Earth's atmosphere (very thin - less affected by wind and less of a danger) or outer space (very thick, to be able to recover from damage from debris). The ribbon would stretch from a base station to approximately 125,000 km to geosynchronous earth orbit, at which point there will be a counterweight - initially the spacecraft used to deploy the ribbon and eventually an orbital station. The climber drives up the ribbon with an electric engine, and will need to be powered wirelessly. Currently the predominate thinking is to use a laser to hit solar-panels on the climber that are tuned for the particular wavelength of light that the laser is emitting. Initial Space Elevators, built in about 10 years for about $10 B, will be able to carry 20 tons of material at a cost of ~$300/kg (contrast that with the next-gen shuttle - $100 Billion, with a capacity of 40 tons @ ~$10,000/kg), with subsequent elevators able to carry up to 200 tons at a cost of $100/kg.

Re:Intro to Space Elevators

[GodSpiral]

1 m/s takes 34+ days to go up 125000 meters. 35,786 km is the altitude this link (http://science.nasa.gov/headlines/y2000/ast07sep_ 1.htm) gives. That would take almost 10000 hours(416 days) at 1 m/s. A reasonably practical 8 days at 50 m/s (180km/h).

It takes a ton of energy to climb alot of weight. Going slowly can help cut down air drag, and so can not having to lift the energy source and motor, but anchoring to the rope is probably antithetical to going up fast, and it will need some speed (~180 kmh) in order to have any practical value.

Re:How do they work?

[Leebert]

A station close to Geosynchronous orbit will be in microgravity.

More specifically, at the equator it would be geostationary orbit.

Re:How do they work?

[endemoniada]

Thankyou for your insightful explanation.

I just wanted a short, to the point, explanation of how it worked, and that's what I got. Google and Wikipedia in all honor, but when you REALLY want something explained, you post a Slashdot comment! :)

It's the music!

[The-Bus]

The problem is the music. We can all stand elevator music for a few seconds, maybe a minute or two. But could you imagine dealing with it for hours? We'd all go stark raving mad!

Re:It's the music!

[Sigg3.net]

Survival of the fittest, no doubt.

Re:How do they work?

[CastrTroy]

I think that the reason that we have no space elevatos is the same reason that we haven't been to the moon in 30+ years. Nobody has made it a priority. Kenedy made it a priority to get to the moon, and NASA got the necessary funding. Lately presidents haven't been willing to spend so much money on space exploration, but would rather spend money on things like national defence.

How long does it take to measure 60 meters?

[aplusjimages]

Just curious why it is taking so long to measure the the ribbon to see if it was 60 meters or 50? Is there a specific process to it?

Re:How could you do this now?

[OriginalArlen]

Son, I'm sorry to break it to you, but just because something can be imagined doesn't mean it can be built. Yes, Veronica, that means that science fiction is not necessarily a cast-iron guarantee of new technologies that will be invented real-soon-now. In fact when it comes to Space Elevators I'd bet every penny I have that they will never happen.

Now, turn that TV off and go and tidy your room.

Re:How do they work?

[CastrTroy]

Well, according to wikipedia, the size of Delaware is 6 square Kilometers. If it gave us an easy to way get things into orbit, I think that it would be worth giving up such a small piece of land.

Re:How do they work?

[Anonymous Coward]

Er....

If the weight at the end is in geostationary orbit, how is it exerting any kind of force to tension the line? Isn't the whole point of being in a stable orbit the balance of forces?

The weight of the line itself will try to pull it out of orbit, climbing robots etc. will try to pull it out of orbit - hell, the drag of the jetstream will try to pull it out of orbit.

There is no way that this space elevator lark is going to work without thrusters on the head end continually applying tension to the line - this technology is going to be far from a free ride.

I'll expect to see it working about the same time as I pass my flying car license.

Why electric?

[Nuffsaid]

Why this fixation on electric motors for the climber? The travel takes way too long this way. Use rocket engines, I say. Fast, solid, space-proven technology. Plus, you might be able to avoid the tether construction entirely!

100 metre

[hey]

Why not make the first challenge a 100 metre elevator. Which is still pretty tall.
There would have to be some weight restrictions. Build a tower that tall and see who can
climb up.

Re:How do they work?

[lgw]

The station is in geostationary orbit. The counterweight is beyond geostationary, exerting considerable tension on the cable.

Re:How do they work?

[MachineShedFred]

O Rly?

Area Ranked 49th
  - Total 2,491 sq mi
(6,452 km)
  - Width 30 miles (48 km)
  - Length 100 miles (161 km)
  - % water 21.5
  - Latitude 3827'N to 3950'N
  - Longitude 752'W to 7547'W

( source: http://en.wikipedia.org/wiki/Delaware )

couldn't they just

[s-gen]

...send the next payload up "out of phase" with the oscillation caused by the first one? (its good that space elevators can swing back'n'forth btw... thats how the one on Mars is gonna avoid getting hit by Phobos).

Re:couldn't they just

[lgw]

You too can try the experiment!

Step 1: you need a long pendulum with a heavy bob, hanging a string from the suspended ceiling at work is a good plan, and you stapler is about the right weight.

Step 2: you need another heavy weight about 2 feet up from the first to simulate the wieght of the station. Borrow your neighbor's stapler too.

Step 3: get the pendulum swinging at least a yard in either direction. Now try to stop it from swinging, but you're only allowed to push on the middle of the string, and you have to push in the same direction for several back-and-forth cycles of the pendulum.

Step 4: OK, that was a bad place for your monitor, pick it up off the floor and put it on a different spot on your desk. It probably still works.

Step 5: explain to your boss the redeeming scientific value of this important experiment!

If we ever want to build an elevator on Mars, we'll just have to grab Phobos and use it as the counterweight, because sadly the elevator will be swinging in the wrong plane to dodge Phobos.

Why not a moon ladder instead of a space elevator?

[nsandland]

With all the talk about space elevators lately, it's gotten me thinking why we wouldn't also consider the problem from the opposite angle: start at the moon and go down to earth. We could attach a rope/ribbon/ladder/whatever at the moon, then dangle it down into the earth's atmosphere. Naturally we couldn't attach it to the earth due to the asynchronous movement of the two bodies. So instead, we would dangle the ribbon in the air and use an airplane to fly up to it's end.

Some advantages I see in this approach would be that:

1. The earth's gravity would be much stronger than the centripital force of its rotation, for keeping the ribbon taut.
2. We could hang the ribbon high enough that it wouldn't be subject to weather problems, as would a ribbon which starts at the ground.
3. The moon is a useful destination.

Has any research been done into something like this? Is it viable (at least as viable as a space elevator, anyway)?

Re:How do they work?

[Shadowmist]

Compared to this project, the moonshot doesn't even approach cakewalk status. You have absolutly no comprehension of the sheer physical size that this would entail.

Re:How do they work?

[CastrTroy]

sorry, i meant to type 6000, either way, it's a small piece of land if the space elevator works as well as it should.

Re:How could you do this now?

[Anonymous Coward]

In theory, that's true. In practice, however, science fiction has been a pretty good predictor of technology to come. It's not 100% (yet), but quite often, the 'super high tech' stuff of sci-fi is developed a few hundred years *before* the sci-fi predicted it would be. As for most of the rest? Well, we're running a bit late on actually *using* flying cars, but the technology for them exists.

Re:Why not a moon ladder instead of a space elevat

[Anonymous Coward]

The height of the moon from earth varies greatly, so then you'd have to make it variable length, and it moves at a pretty nice clip over the earth, creating problems with trying to attach anything to it.

Re:Why not a moon ladder instead of a space...

[Ulven]

On the very remote chance that you aren't a troll, the moon is about 10 times further away than geostationary orbit.

This isn't even the biggest problem with your proposal.

KISS

[slashmojo]

Keep It Simple Stupid

Just build a space ladder.. and then you could lose some weight on the way up to space. ;)

Re:How could you do this now?

[drinkypoo]

(and when/if we get there, there are heat properties that I always wonder about in a space elevator, for instance a photo flash is enough heat to ignite loose nanotubes)

Those are loose nanotubes. I have another experiment for you: Get a 3" square of some copper screen, made with a fairly small wire. Try to melt the center of it with a lighter; experience defeat. Now pull one wire out of the mesh, and try to melt it with a lighter. You will succeed. In that moment, the student will be enlightened.

Re:Why not a moon ladder instead of a space elevat

[Anonymous Coward]

This wikipedia article has some interesting references on a lunar space elevator. I think there ought to be an X prize for that specific accomplishment. This is the sort of think that might be relatively economical in a few years. Just getting a stable prize in place could easily accelerate the time this would get accomplished by several years. What a lunar space elevator means is that suddenly, it becomes a lot more economical to get various forms of mass to orbit. It would still be expensive to get people up there,but a lunar space elevator would be a major infrastructure item helping to make large structures in orbit.

Re:How do they work?

[budgenator]

obviously the "easiest" way would be to put a cable factory into geosync orbit then and make the cables, then there are two different ways to do it;
1. make two cables one going down, and one going up to counter-ballance. after a while the downward bound cable touches the ground and gets tied off you keep making the downward a bit longer to stand-off the countermass from the geosync point. Then if possible You then add mass to counter-ballance and reel in the counter-mass cable as you go. once the counter-ballance cable is all reeled in, you detach it and fly it over to elevator station 2.
2. you take a reeled cable manufactured is space and carefully unreel it to the ground while keeping the center of gravity at geosyncronus orbit.

This is conceptually simple and elegent, but the engineering will be mind-boglingly difficult, I doubt it'll ever happen because we've never have a material with enough strength to mass ratio. Imagine how much static electricity a cable that long would gather, it would be the world's tallest lightning rod.

That's a big Twinkie.

[kureido]

Today's fun fact: a mole of Twinkies stacked end to end, assuming they're about three inches long (I haven't one around to measure), would stretch from here to Andromeda and about 90% of the way back.

Re:That's a big Twinkie.

[rkanodia]

Well duh. Don't you think the GP thought of that? A tower of twinkies stacked end-to-end would NEVER stand up. You have to lay them down on top of each other, lengthwise!

Sheesh, some people, always trying to take the easy way out...

NASA's units off again...

[Nanoda]

So you can't play if you're off by a millimetre, but if they're off by 10m or so, that's ok. :-P

When physics hands you a lemon, make lemonade.

[Ungrounded Lightning]

You also have to handle the oscilation modes of the cable as a plucked string.

Seems to me you can turn this to your advantage:

Initially the climber plus payload pulls the counterweight back - but then it swings forward, converting a backward momentum delta to a forward one, which you can then use to accellerate the payload further with more climbing. When you get to a decent release point you can also wait until you've got extra forward momentum to help circularize your orbit or improve your launch, and let go then.

You end up with the whole thing in some combination of string vibration and pendulum oscilation. But you can damp much of that out on the climber's way back down - unless you want to deliberately leave some of that energy and momentum in the elevator's motion for use by the next payload.

The point is that by modulating the climber's travel rates you can move energy and momentum among the vibration modes, payload motion, and Earth's rotation, ending up up dumping it into the payload, where it's useful, rather than accumulating it in the cable and counterweight until you pull the counterweight out of orbit.

Devil's in the details, of course. You'll need a bunch of computation and to tweak it with feedback measurements from payload to payload. (If nothing else, wind loading will pump up the vibrational modes.)

You might also put "dampers" on the cable. In particular, by letting part of a climber's mass move sideways with the cable and part lag behind you can collect vibrational energy at the climber, damping it out of the cable's motion, and using it to generate power for more climbing. (Or avoid the extra gear on the climber by doing it at the ground station - letting the attachment move along a track with a generator/motor/actuator attached, to damp out the reflection by recovering the power.)

It might be interesting to analyze how much energy you could send up the cable to the climber by shaking it. (Probably not enough. But worth a look - especially if the cable is not prone to fatigue.)

Re:When physics hands you a lemon, make lemonade.

[Ungrounded Lightning]

Yes, I know:
  - you don't need to "circularize" if you get to geosync altitude,
  - somewhere below that you can let go and end up with an eliptical orbit with perigee sufficiently above the atmosphere, and
  - energetically, if you want to head out it's better to climb PAST geosync and take off than to let go sooner and use some thruster.

But using the momentum from the tether's vibration lets you cut loose lower, reducing the amount of space-elevator time needed to achieve your goals. Space-elevator time is, IMHO, likely to be a scarce enough resource that the best price-performance might be accomplished by minimizing it at the cost of more propultion on the payloads once you get them out of the atmosphere. And even if not, it will be non-zero cost, so you'll want to cut loose as soon as your payload can be given the needed momentum.

kg of force?

[Anonymous Coward]

So team member Bryan Laubscher quipped before the informal tether pull: "I cannot measure, but I can tie a hell of a knot." His tether broke after 240 kilograms (529 pounds) of force was applied.

I don't think the writer can measure either. Kilograms are not units of force.

more brilliant than it may appear

[GodSpiral]

In terms of energy required, it takes the same amount of energy to climb at 1 m/s as it does at 1km /s. The difference is in air resistance that is very high at high speed (function of v ^2).

The only benefit of the thether system is that it allows slow speed climbing. For some reason, we don't value trains that go 1 m/s, and if they can't have climbing bots go up and down on the same thether, which would indeed seem like a big complication, and there's no room in space to store a bunch of robots so you can send them all back down at the same time, then you can only bring a small payload up to space every 10 days. The reason trains don't go 1 m/s even if it saves fuel is that efficient track utilization is important too.

It might take decades in order to get sufficient payload totals up there to justify (as in break even on) the energy savings of building the thethers, and its not clear that these cables will last decades.

Re:more brilliant than it may appear

[GodSpiral]

turns out practical speeds for these things are 180-200 km/h, which pretty much makes the thether friction a slowing force with no help "holding up" the climber, and so if powering by lasers/microwaves from the ground is the needed breakthrough, then the thether part isn't needed.

Considering the innefficiency of lasers multiplied by the innefficiency of solar panels, if a thether is useful, then an electrically conductive power transmitting thether is necessary. Powered in part by slowly falling (braking) climbers on the other end.

a word from a participant

[Anonymous Coward]

I was one of the team leaders for one of the elevator games teams. The article linked here gives some sense of the incompetence of the competition organizers, but the truth of the matter was far worse. The climber challenge was fraught with late/nonexistent equipment, no parity in the rules between the teams, vague rules and inaccuracies along every step of the way. The tether strength challenge was a joke, with professional organizers funded by NASA failing to properly carry out a test that any science/engineering student could do in first year.

To give an analogy, dozens of teams put thousands of dollars and hours into building race cars, only to show up at the venue and find that instead of a formula one circuit there was a dirt track through a cornfield. Our team spent thousands of hours on our entry and so did all of the other participants. It's too bad the organizers couldn't have repaid this dedication and passion with a small amount of their own effort.

Re:a word from a participant

[ExFCER]

"...only to show up at the venue and find that instead of a formula one circuit there was a dirt track through a cornfield."

Should I sigh or is this insightful?

All problems demand that we look for more than just the standard solutions. That is what this/these test(s) is/are about...

Re:How could you do this now?

[Anonymous Coward]

Shows how stupid you are that you offer a bet that you can only lose.

Re:How could you do this now?

[Iron Condor]

Why was that modded "flamebait"?? It's the first realistic comment in the entirel thread!

Re:How do they work?

[Iron Condor]

The station is in geostationary orbit. The counterweight is beyond geostationary, exerting considerable tension on the cable.

If it is beyond geosync, then its orbital period is larger than one day. The "tension" it will exert on the station is thus not radial away from the earth but towards slowing the station down. Slowed down, the station will fall closer to the earth.

The whole thing will simply wind up around the planet.

And at all of /. there's nobody capable of doing the imple math to recognize that.

Pitiful, really.

Re:How could you do this now?

[OriginalArlen]

That comment was modded flamebait because it asserted that Space Elevators will never be a practical proposition, and further suggested that many people seem to assume that technologies seen in science fiction are merely a matter of time. These ideas are antithetical to a certain subset of Slashdotters, the ones who post to stories about space elevators, Mars colonisation, interstellar spaceships and the like in particular. They really don't like the idea of hard limits imposed by physics. It seems to upset their notions of Manifest Destiny...

Re:How do they work?

[MichaelSmith]

The Fountains of Paradise by Arthur C Clarke is well worth reading. He describes in detail a space elevator project in a future (and slightly modified) Sri Lanka.

Re:How do they work?

[MichaelSmith]

If it is beyond geosync, then its orbital period is larger than one day. The "tension" it will exert on the station is thus not radial away from the earth but towards slowing the station down. Slowed down, the station will fall closer to the earth.

It is not in orbit. It is tethered.

Calling Mr. Otis, Calling Mr. Otis

[jman.org]

It's an elevator, for cripe's sake. We've had them since the 3rd century BC. They've been reasonably safe for over 100 years now.

No new technology is needed for the car itself.

There are two problems to solve: Suspending enough cable outside the gravity well so that it won't fall back to earth, and keeping it 'straight' as it's whirled round 'n round.

Neither of those two things can be tested by a model. At least, not here on Earth, as our own gravity would skew the results.

The car itself, along with the drive mechanism are both proven technology, used in every high-rise across the planet.

So, string the big cable (made of BuckyBalls, perhaps?), mount solar panels up top to take care of the electrical requirements, and off we go.

The really exciting thing here would be if it could actually be built soon enough for Arthur C. Clarke to actually ride in it, similar to the way he was able to use his home satellite dish in Sri Lanka to fax chapters of 2010 to his New York publisher...

Bzzt

[ishmaelflood]

It is not in unrestrained orbit. Pitiful really.

Nanotech?

[ishmaelflood]

I'd have thought megatech or gigatech would be more appropriate for a thing umpteen thousand miles long