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If I had a ladder capable of withstanding the forces placed on it, wouldn't eventually I reach a place where the earth's rotating caused me to reach escape velocity? As the attached object was farther away it would have to spin faster to keep up with Earth and then would at some distance be faster enough that if one let go they would escape Earth's influence, right?
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Yes, you are correct.
The concept you are talking about here is the same as the space elevator, and there are various versions of this, tethered or non tethered. You could build the ladder up from the ground, or put a mass into orbit, drop the ladder over the side and feed it back down to the ground, and then tether it!
Have a look at this wiki link, it has references to the different methods and uses that may be possible.
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You can compute that altitude using cuberoot(G*M*2*period^2/(4*pi^2))-r, where G=6.673e-11, M=mass of Earth = 5.98e24, period=86164 seconds (sideral day), and r=Earth's radius=6378000m. You'll find your ladder needs to be about 61,000 km tall.
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I just perused the Wiki link and don't see a reference to an idea of a tether based in GS orbit, ending inside the atmosphere, and low enough to place cargo from a high-flying winged aircraft.
I supposed this idea has been put up and shot down already.
Order of Kilopi
If the tether comes down from geostationary orbit, then the Earth end of the tether will be stationary with respect to the ground, so trying to rendezvous with it in an aircraft would be difficult (the aircraft would be moving too fast). You could rendezvous with it more easily in a balloon, and this idea has been proposed seriously.Originally Posted by Pinemarten
Or you could have a tether not in GS orbit, and have the tip move at the required speed; the Skyhook concept describes something along those lines.
http://en.wikipedia.org/wiki/Tether_propulsion#Skyhooks
Banned
Problems with the strength of materials and atmospheric movement, or dragging seem to be a problem for this idea to get off the ground.
Do we want to build a lightning rod that big?
There must be some very good reasons why this could not work. or it would have been done all ready.
Order of Kilopi
As speedfreek and others have mentioned, you can search for "space elevator" and "rotovator" if you are inclined to do your perusing for information.
Quite vigorously... astromark has lightly touched on a few issues. A quick google of this site offers quite a few discussions with many pros and cons.
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Carbon nanotubes are strong enough to build a practical space elevator (with sufficient taper you could use steel, the required mass is impractical though). Atmospheric drag isn't an issue as the cable will be stationary relative to the Earth, and atmospheric movement (ie winds) can be coped with easily enough so long as you avoid the areas prone to major storms.
That can be solved easily enough:Do we want to build a lightning rod that big?
A) Start from the top of a mountain above most of the weather (which is a good idea for other reasons as well).
B) Use the same sort of solutions as are already used for high antennae.
Money is the main one, the other big one is that no one has yet figured out how to grow long enough carbon nanotubes or to join them together (its being worked on though, there are a huge number of potential uses other than orbital elevators). There are companies working on building orbital elevators, for example the Liftport group.There must be some very good reasons why this could not work. or it would have been done all ready.
Order of Kilopi
Oh boy, the religion of space elevatorism... here we go again...
Taking individual issues, discussing them ad nauseum, and not looking at the big picture of these X things need to be considered, and here are the Y things that will be needed to overcome them.
Banned
I began this space elevator vs rotovator thread a couple days ago to discuss just such pros and cons.
Order of Kilopi
Ah good; haven't got that far yet (away for the weekend).
Order of Kilopi
The real problem with this idea is the object wouldn't be in orbit-- it would be hanging from a ladder. We can always hang this from other things if the materials are strong enough-- what we want is to achieve orbital speeds.
Order of Dr. Kilopi
what does Coriolis say about this?
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It's amazing that lightweight ropes are starting to approach the incredible strength/weights needed for such a venture. Whether they will ever bridge the gap between now and what's needed is yet again a problem - and no telling what would happen to any material of such fine avanced structure needed when exposed to temperatures radiations and electrical differentials. Also, it would seem that to get to stationary orbit, the slow travel through the radiation belts (van allen) could be fatal for elevator riders.
While it makes for intriguing scifi - and who knows - maybe there is some place other than earth where it's practical - the view of watching some rope that looks like something pulling a skier from a water ski boat picking up a half dozen vehicles off the ground is just astounding.
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There is a certain existential attraction to the idea of climbing into space...one rung at a time
Order of Kilopi
This image gives an idea of the coriolis effect; it causes a displacement in the cable as the climber goes up or down.
http://en.wikipedia.org/wiki/Image:S..._of_forces.png
If the mass of material going up is about the same as the mass going down, this force would even out over time (not without causing some lateral movement in the meantime), but in the early days of space elevator operation a balance is unlikely. So the design would have to accomodate some displacement; more wiki info here
http://en.wikipedia.org/wiki/Space_e...and_cable_lean
from here the coriolis force acting on a climber at 695 metres per second is given as 0.05 g
http://www.halfbakery.com/idea/Elevator_20to_20Space
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What is the orbital speed of an object in geostationary orbit relative to the ground?
The elevator can also be used to access lower orbits as well, drop off the cable below GSO and Coriolis forces will push you into an elliptical orbit which you can circularize with a high efficiency, low thrust engine. Though of course the use of orbits below GSO would have to be restricted due to the risk of collisions with the elevator cable.
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Unless of course it was tested first, both using physical testbeds and computer modeling (carbon nanotubes actually have a really simple structure).
That is a definite problem, the solution though is quite simple, add shielding to the passenger cars (its cheaper to make cargo sufficiently hardened to nor need shielding), the problem is that it would use up a large portion of the mass budget,particularly for early versions of the elevator, but that is probably acceptable as mass wise humans aren't likely to be a major item being sent up.Also, it would seem that to get to stationary orbit, the slow travel through the radiation belts (van allen) could be fatal for elevator riders.
A more intractable problem is that there is a significant region of the elevator where in the event of an accident like the car falling off or the cable failing passengers would inevitably die because they would reach too high a speed to survivable renter the atmosphere and don't have enough radial velocity to go into orbit.
Wrong type of orbital elevator, that view would only occur with a rotating tether, the version of orbital elevator being mostly discussed so far in this thread is a static one that would look like the Indian Rope Trick done on a grand scale, a cable disappearing into the sky with no visible support for it.While it makes for intriguing scifi - and who knows - maybe there is some place other than earth where it's practical - the view of watching some rope that looks like something pulling a skier from a water ski boat picking up a half dozen vehicles off the ground is just astounding.
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existential attraction? Sorry, 126 million rungs doesn't ring my chimes. What was that existentialist short story of the room full of people that didn't like each other - the existential version of hell if I recall?There is a certain existential attraction to the idea of climbing into space...one rung at a time
An elevator would be bad enough. New variations for the bottles of beer on the wall. 21,296 bottles of beer on the wall ....
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That's 5916 rungs per bottle
I would need a bottle of beer a least every 1,000 rungs, minimum
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Grashtel,
That last quote of mine about the cars wasn't about the elevator, it was about the rope that is currently available. It looks like a rope one might use for water skiing - in fact, being lighter than h2o, it floats and hence is suitable but rather overkill. Some manufacturer did a commercial picking up half a dozen full sized vehicle using one of these ropes that looks like it could be a plain old water ski rope or something you might tie down a tarp with in the back of a pickup truck.
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With that much beer, probably don't need to worry about the van allen belt radiation.That's 5916 rungs per bottle
I would need a bottle of beer a least every 1,000 rungs, minimum
Order of Kilopi
I think you missed my point-- I was talking about the question of dangling something low enough for an airplane to reach it. That's not an orbit at all.
But seriously, the space elevator is a positively absurd idea, and it will never happen. It's about as likely as warp travel, and it's needed about as badly at this particular moment in the human story.
Order of Kilopi
There are a number of tether concepts that would be in orbit and would dangle a cable end low enough and slow enough for an airplane to reach it. Study up on "space rotovators" for one. The synchronous tether, with a counterweight above GS orbit could have the cable end in the air, or on the ground. Of course, there wouldn't be much point in having airplanes reach it.
The space elevator is physically possible, the primary show stopper at this time is the strength of bulk materials. However, carbon nanotubes demonstrate that such materials are possible with development. It is unreasonable to compare it to a warp drive, which is not physically possible.But seriously, the space elevator is a positively absurd idea, and it will never happen. It's about as likely as warp travel, and it's needed about as badly at this particular moment in the human story.
Last edited by Van Rijn; 2007-Apr-24 at 01:44 AM. Reason: Removed editorial comments
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
The Leif Ericson Cruiser
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It is if what you are dangling is a 35,786 km long cable (with an appropriately massive counterweight going outwards), in which case the center of mass is in geostationary orbit and the end of the cable is able to be anchored to the ground so it can be scaled.
Try learning a little more about orbital elevators before you decide that its "a positively absurd idea" you might just be surprised. Being able to charge merely hundreds (as opposed to something like ten thousand now) of dollars per kilogram to get into orbit while still making big profits seems like it might just be something a business might want. Unlike warp drive an orbital elevator doesn't need any major new developments, we already know how to make nanotubes strong enough for a practical OE, we know how to fuse nanotubes together to get very long ones, and spinning nanotubes into a cable is being worked on.But seriously, the space elevator is a positively absurd idea, and it will never happen. It's about as likely as warp travel, and it's needed about as badly at this particular moment in the human story.
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Payload of the car is a consideration. I am thinking; provided the elevator gets done, there will be an interesting exercise for students of the future working out what has to happen as a car rises and the system's centre of gravity moves.
Order of Kilopi
Hardly. The show stopper, even with unlimited tensile strength, is the completely unproven status of the concept. Safety issues, feasibility surprises, and environmental impact have been hardly touched. This is a freshman physics problem gone amuck. Time for some skepticism, folks.
I'll give you that-- you can't make a freshman physics problem out of FTL travel. That's pretty much the difference I see. Maybe people are "playing" with this idea, wondering if we'll need it or use it in 500 years from now. But in our lifetimes, or our children's? Hey, UFO aliens are also physically possible, perhaps that should have been my comparison.It is unreasonable to compare it to a warp drive, which is not physically possible.
Order of Kilopi
And Leonardo Da Vinci had the the basic principles, from studying birds, to learn how to fly. But his method was completely unproven in practice, and suffered from all kinds of safety and scalability problems that killed a lot of entrepreneurs until the Wright brothers figured out how to do it differently, 400 years later. So let me just ask you, what time frame are you looking at for this?
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One practical consideration is that the ladder/elevator must be stradled to the equator...I think (seems intuitively obvious)
The question is, are there any satellites in orbits that do not have equator-crossing orbits? In other words, are there any satellites for which there is no chance of clipping the ladder at some point?
Is there a Los Vegas bookie in the house? What are the odds of a stationary ladder not getting in the way of present and future orbiting gadgets?
Order of Kilopi
Orbits follow a great circle around the Earth (eccentricity may make this a littl off, but the overall effect is still a great circle.
The equator is a great circle.
There is no way that great circles can be parallel (non-crossing).
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