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Highlift Systems' Space Elevator In The News Again
Kris_J writes "Highlift Systems may have found a second location for the anchor of their space elevator -- Perth, Western Australia. Apparently we have the calm waters and international airport that it needs, amongst other things. Slashdot has covered this company's efforts before: Oct 9, 2002 and, earlier, August 13, 2002, but it's worth discussing again since '[recent funding] has been given momentum by the Columbia shuttle disaster.'"
Think of holding a string with a weight attached to the end of it. Now swing it around your head. The faster you swing, the more horizontal the string becomes. It's the same effect with this 'space elevator'. The idea is to have an asteroid or some other heavy body attached to the end of the space elevator, and as the earth *swings* it around, the force of that weight on the end is supposed to keep it in place.
Obviously, there has to be a pretty good anchor in the ground for it not to go flying into space.
will SOMEONE explain to me how such a thing is supposed to work?
In a nutshell, the center of mass of the whole elevator, including ribbon and cargo, is at (or near enough) the radius which provides geosynchronous orbit. This can be achieved and maintained in a number of ways, all of which are irrelevant details once you grok what 'geosynchrony' and 'orbit' really mean.
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The earth is spinning. At ~100miles, it's moving very, very, very fast. The centriptal force created by that motion will hold it out. I don't know the specific speeds and forces offhand, and I'm too lazy to get my physics text off the bookshelf.
To give you an idea, get a weight and tie a rope to it. Spin in a circle. Notice the weight pulls away from you and stays steady? Now, you could build a little robot to move up and down that rope (while you are spinning it). That's how it works. The forces are astronomical though, and the materials science problem is why it hasn't been attempted before.
..don't panic
The other possibility sometimes mentioned is electrical charge. The differential over a long length of conductor inserted into the Van Allen belt could provide enough charge to suspend it.
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
http://www.howstuffworks.com/space-elevator.htm
Centrifugal force. I have the .pdf file, the examination on the plausability of this working. The cable would be 60,000 miles long. At this length the force of the Earth spinning would hold the end of the cable outwards in a straight line.
The first cable would be 1 micron thick, and taper from 5cm wide at Earth to 11.5cm in space. This would be added to each climb. By the 107th addition it would be capable of holding a climber of 22tons with a 14 ton payload.
Of course it would be made of Carbon nanotubes (the only thing that could possibly be strong enough and light enough).
Now I'm not saying I believe it can or will be done. I'm only quoting Bradley C. Edward's paper.
My guess is you have to put a weight on the end out just far enough away from geostationary orbit to counteract the downward forces.
Jeremy
The top end is actually above orbit, such that the center of inertia of the entire thing (elevator included) is in orbit (adjusting for the different gravity over the length of the cable, of course). So the real answer is that there is excess upwards force, but the end can't fly off because the cable holds it down. Then the elevator pulls against that force.
It's not a stupid question. Get a ball on a string and whirl it round. The ball doesn't lag does it? The outward pull of the ball keeps the string taut. The exact same effect will be used by the elevator. Locally, in the atmosphere, the cable will be stationary, so it will have to resist wind loads, but they have worked those out. There is also some drag due to space debris and solar wind, but again they have accounted or that.
Good article, nice website, fantastic project. As Arthur C Clarke said (I think, loosely), we'll be using a space elevator about twenty years after everyone stops laughing at the idea.
Not stupid at all, accurate actually. See their FAQ .
The second paragraph ends with:
It's kinda neat that they used Australia as an example (I read their FAQ a few days ago, before this decision about putting it near Australia was published; they didn't change the example for this recent news).
OT: the fortune at the bottom of the page is very amusing: "Mr. Spock succumbs to a powerful mating urge and nearly kills Captain Kirk." -- TV Guide, describing the Star Trek episode _Amok_Time_
I feel fantastic, and I'm still alive.
First of all, theres no way that the structure could be supported solely from the ground, the bottom is anchored, but thats not why its rotates with the earth. Rather, the top is anchored to some heavy object (read asteroid or the like) that is (somehow) placed into a geosync orbit. The structure merely provides a way to efficiently travel from earth to the other object (as you have a solid medium to push against and facilitate the change in grav. potential).
P.S. Yes, technically the orbit of the top of the elevator/upper anchor is not geosync, but rather slightly above geosync to allow for the center of mass of the contraption to be geosync in its orbit, (and the bottom anchor then serves to maintain the proper orientation).
**AA: a bunch of mindless jerks who'll be the first against the wall when the revolution comes
Exactly. The damage done by a broken orbital elevator depends almost entirely on where the break occurs. Red Mars had such a terrifically destructive event becuase A) the thing was far heavier than anyone is planning for use here and B) it was cut on the far side of its center of mass. Orbital mechanics dictated that it would go nowhere but down. If the thing had been broken on the other end of its center of mass, then (barring the piece that was severed) it would have gone _up_ instead. Which would make it a hassle to reestablish, but not the latitude-destroying event Robinson depicted so well.
Dyolf Knip
Any local Perth residents that want anything to happen with this project should send a message to the Premier's office using this page. Be polite. (I'm fairly sure this isn't redirected to /dev/null.)
There's no reason (in theory) why the bottom has to be anchored to the ground (although it probably would have to be to reduce tension on the elevator material). Ideally the elevator could be set up so that the bottom would hang a few feet off the ground in midair.
There's also no reason why the top would "lag behind a bit". In fact the orbital speed of the counterweight will tend to increase, not decrease, if the orbit decays below geosynchronous orbit. So it would tend to lag forward, not behind. It would definitely need a transport system to carry rocket fuel up to the counterweight for corrective thrust.
The real reason why one hasn't been built is the extreme material strength required. Nobody has yet developed a material that can hang suspended for a length of 30,000 miles without breaking. This is why most designs count on the bottom of the elevator touching the ground, so that a significant portion of the elevator's weight can be supported by contact with the earth instead of tension in the elevator. Another mitigating factor is the weightlessness of the material at high altitudes- the parts up near the counterweight hardly contribute any tension at all and can be built especially thick. Even with these two caveats, the required tensile strength is so high that people still talk about exotic materials like buckytubes and single-crystal metals whenever the topic of the space elevator comes up. Without some breakthrough in materials engineering, the project is essentially hopeless.
More info if you are interrested can be found at http://science.howstuffworks.com/space-elevator.ht m
Space elevators are central to Robinson's 'Mars' trilogy as well ("Red Mars," "Green Mars," "Blue Mars"). Highly recommended if you're into Mars. ^_^
And all our yesterdays have lighted fools The way to dusty death. --Will
There is NO SUCH THING as "centrifugal force". "Centrifugal force" is the effect of tension in a cable against the center of rotation caused by CENTRIPETAL force accelerating the swung object towards the center.
It's like this...a car pulls a trailer. The car is pulling the trailer! There is a force acting backwards on the trailer hitch on the car, but it is actually the car pulling the trailer, not the other way around. The anchor is not pulled by the swung object, the anchor PULLS the swung object.
If the string is cut, the object does not accelerate away from the anchor because of some centrifugal force; the object will STOP accelerating and continue along in a straight tangential line.
Centripetal force is real, centrifugal force is apparent.
I believe it's a three day trip.
Simple. Just like the shuttle did, it would burn up in the atmosphere and break up. Maybe the lower portion of it would have some explosives to blow it into little pieces if it ever came apart (since it wouldn't be high enough up to burn up), but this is part of why it would be ocean-based (then, if it did fall the only people upset would be the environmentalists)
If this is built out of carbon nanotubes, like people suggest, then its possible they could be woven together in such a way that if any point broke, the chain would come apart in many places, so that a lot of little pieces would fall, however the extra length/weight of tubing required for this might make it prohibitive.
If I have been able to see further than others, it is because I bought a pair of binoculars.
Start with an elevator starting in perth, sticking out parallel to the equatorial plane. Have the end attached to a meteor or something (I think it would work the same either way, but this way is easier for me to visualize). Let gravity pull the meteor pull the end of the elevator back toward the equatorial plane, resulting in a sort of curve that starts parallel to the equatorial plane in perth, and ends up somewhat south of the equattorial plane, held in place by tension.
I'm not sure if this works, physics-wise, it's just what I visualized. I'm sure someone here can bust out some equations for us, and tell us what would happen!
What's that sound? Why, it's just Isaac Newton, spinning in his grave fast enough to power a city...
Velocity exerts no force. The orbital anchor will "want" to fly off straight at high speed. The (currently wundertech) carbon nanotube cable, attached to it, suffers a tension. The Newton III complement to this tension pulls the anchor toward the Earth. This imparts an acceleration exactly balanced so as to cause the anchor to execute a circle about the center of the Earth.
It's only been 320 years since the Principia. Maybe someday soon we'll catch up to Newton.
The Mongrel Dogs Who Teach
The above post makes an excellent point, there is currently no material that can sustain the enormous stress that would be required to construct a space elevator.
While there is no current material that yields the necessary strength/mass required in order to built a space elevator, realistic possibilities are on the horizon. Quite simply, with the advent of nanotechnology, we are nearing the technological feasibility of creating a material composed of intertwined nanotubes. This is theoretically the strongest material that can ever be created. Carbon-Carbon bonds are extremely strong and would be extremely densely packed in a nanotube pole. It would be an order of magnitude stronger than steel, as well as significantly lighter.
While nanotubes can already be readily produced (Dr. Smalley of buckyball fame operates a production facility), strong nanotubes rods have yet to be produced. This is due to a variety of technical hurdles that must still be overcome. Perhaps the foremost obstacle is getting the produced nanotubes to lie parallel to each other. The current production method has the nanotubes forming from a catalyst and then becoming intertwined in a jumbled mess. When tension is applies to the mesh, the rope breaks not within the nanotubes (which would require a great deal of energy), but between the nanotubes, unraveling them from each other. Attempts to get the nanotubes to align properly have failed. Nanotubes are not an easy molecule to work with. They have extremely strong cohesion forces and are very difficult to pull apart from one another. The obvious approach of functionalizing each nanotube in order to orient it correctly doesn't work as doing so causes the nanotube to lose much of its mechanical and electrical promising properties.
In addition, when nanotubes are put under extreme mechanical stress, the bonds within the nanotube shift. For example, I've seen simulations where the bonds separating two polygons disappears, creating what appears to be a bonding who in the nanotube. The hole then resonates through the nanotube causing significant weakening in the structure.
At a talk I attended, the most promising idea I heard discussed was a steel/nanotube alloy. The nanotubes would run vertically through the steel, reinforcing the structure in the same way steel rods are often used to reinforce concrete. This would alleviate the risk of the nanotubes becoming unraveled intermolecular while at the same time using their large intermolecular strength to reinforce the structure.
Of course, without any physical models, this is mere speculation. However, it suffices to say that a there are real possibilities of breakthroughs that would allow for the construction of such a space elevator.
Actually, the Moon has a lot of nice resources. Plenty of Gold and diamonds (shocked carbon from lunar 'meteorites' and a less differentiated crust implying *easier* heavy metal prospecting.) There are things, much more valuable than gold or diamonds, however, are on the moon that make such an endeavour worth it.
Assuming you can deal with the ever-present Lunar dust, all you need to do is scoop up regolith and shoot buckets of it down to earth for processing. Unfortunately, getting the first mining and support equipment to the moon, assuming tele-operated rigs, is very expensive.
But, wait...a space elevator could be hauling multi-ton stuff at a fraction of the cost-per-kilo of the equivalently expensive[1] Saturn 5 program (okay, 6.5% of the U.S. gov't annual budget vs. 6% for Neil Armstrong's legendary words.)
[1] total cost is almost equal. But you can use the cable a few more times that you can use a Saturn 5, thus your cost-per trip goes down with more trips.
"You cannot have a General Will unless you have shared experiences. You cannot be fair to people you don't know."
absolutely not true. the elevator is in orbit around the earth just like the moon or any other satellite. the center of gravity of the elevator is in geosynchronous orbit (36000 km or 6.6 ER) Geosynchronous orbit has an orbital period the same as the rotation rate of the earth. A geostationary earth has a period of 24 hours and coincides with one spot on the earths surface. In other words, anything in that orbit will remain over the exact same spot essentially forever. The elevator goes into a geostationary orbit. Since its long, they can put the cable down anywhere within a 45 degree arc. The only thing you need an anchor for is to keep track of the cable. The greatest tension on the cable is at its center of gravity, because at that point, half the cable above it is centripetally trying to be flung into space, and the other half is trying to fall down to the earth. But this is located in geostationary orbit. Theres little if any tension on the cable at ground level.
Unfortunatly you are absolutely wrong. In the example you gave the object is held in "orbit" by the tether. That is most definitely NOT how space elevators work. If it were, "a pretty good anchor" would be something of an understatement. ; )
This is a bit of a simplification, but here goes. In a space elevator, the object at the other end of the cable is in geosynchronous orbit. The cable's purpose is purely for the elevator to traverse. You could take the cable away and the object at the end would still be there*. It is not holding the object in it's orbit - that's what gravity is for.
* Technically, that's not true. Because the cable and cargo have some weight, you have to figure it into the calculations on where the object at the end will rest. It will actually be slightly farther than geosynchronous orbit.
One, if the elevator is to remain in a fixed place above the Earth, the radial force (tension) must balance the inertia. For this to happen, a quick calculation shows that at that latitude, the center of mass of the elevator must be 18% higher than the geosync height over the equator. You'll have to put a massive asteroid into orbit at roughly 30k miles up going thousands of miles an hour to anchor this sucker.
Two, that asteroid will orbit with a 32 degree angle of inclination until it's actually connected to the elevator. I pity the poor fool that has to play catch with that thing in orbit and actually link it to the elevator. If anything goes wrong, the asteroid drops to Earth, bringing devastation on a global scale. All of the previous discussion assumes that the elevator remains perfectly vertical, which brings me to...
Three, if you anchor a space elevator to the Earth at any latitude but 0 degrees (the equator), you're going to have a lateral inertial component, perpendicular to the radial, that'll bend that rope like a taut bow string. Another calculation shows that the shear force on that rope will be almost 53% of the tension. (This is simple trig.) Carbon nanotubes may have a hella strong tensile strength, but has anyone looked at their shear strength? I wouldn't want the thing to snap like a twig just after they get Mr. Doomsday Rock into position to fuck us worse than the dinosaurs...
This post expresses my opinion, not that of my employer. And yes, IAAL.
The post referred to was talking about using Venus's moon(s) for a gravitational assist. This implies a certain minimum size for this hypothetical moon(s), such that the relative momentum difference between your craft and the aforementioned moon(s) is large enougth that you can borrow all the momentum you need without affecting the moon's orbit. Without whipping out the old HP, this is somewhere on the order of "pretty darn huge".
Venus is nice and close and plenty bright. So we would have seen any moon this size by now. So we should feel pretty darn comfortable saying that Venus has no moons.
When you can buy spools of this stuff, it's time to take this seriously. But not yet.
NASA Institute for Advanced Concepts: The Space Elevator
The rock is in orbit above the equator. The elevator starts at Perth. So, the cable/shaft runs at an angle not normal to the earth's surface. It leaves the ground at an angle.
The cable would trace out a cone if it were straight, if that helps you visualize it.
Justin Dubs
Weeeell, yes, just not for very long. I suppose you could build tracks around a meridian and put up with trains constantly hurtling around the planet at over 1000km/h, but it would hardly be economical.
Assuming the original poster was not just practicing rectal ventriloquism, `connected' doesn't mean literally bolted together. You would slingshot a load off the end of the elevator and catch it again on the end of another elevator at the destination. You could also use elevators (even just spinning tethers in free space) to accelerate and decelerate traffic out- and in-bound.
Translation: `I have no sense of scale'. (-:
On top of this, since the elevators are in orbit, they don't make the planet wobble at all (caveat: the mass of the elevators would move the center of mass of Earth, perhaps by a measurable amount).
Got time? Spend some of it coding or testing
The cable simply lacks the required strength to do this. It's made of carbon nanotubes, which are incredibly strong and ligthweigth. Those tubes would however burn up on reentry in the atmosphere.
If some low pieces should somehow *not* burn up, then they would fall very slowly, this is due to the low density of such a cable. Think along the lines of a 5cm wide strip of paper falling. It would not make a huge mess on impact exactly...
Very nicely put. The schoolboy physicist is told that centrifugal force does not exist, so we see it repeated here ad infinitum. The structural engineer (me) knows that the tension in the thread is not a vector, it is a tensor, a two headed vector, if you pass a control plane through the thread there are forces BOTH ways.
A glass of wine with you, sir!
The counterweight is just a long ribbon of the same material.
Launching it requires a rocket launch to past geosynch orbit, reeling out the tether (1mm^2 cross-sectional area) as it launches, the rocket doesn't have to go much past 35k km (geosynch), well at least not the full 65k km, more like 10-25k km before the cable will self unwind to the full extension.
Then a tiny robot (likely solar powered) will crawl up this tiny thread and stick another layer on. And another, and another until it has counterweight capability and strength to lift a 22 tonne lift car and 14 tonnes of cargo. The initial launch is difficult, BUT after that it is just materials and robots... 3 days a piece, after a year it'll be ready... Each robot can haul slightly more cable than the previous robot, which in turn increases its loadbearing capability, and thus more heavier cable... etc...
Z.
There is NO SUCH THING as "centrifugal force".
Centrifugal force is as real as gravity. Under relativity, acceleration due to gravity is simply an artifact of choosing a non-inertial frame of reference.
So is centrifugal force.
So in short, anyone who says that centrifugal force does not exist should also say that gravitational force does not exist. In both cases, the apparent "force" is merely due to a convenient choice of coordinates.
-- Tim Little