Japan to build Space Elevator

It's going to be another rip-off like perpetual motion or hot fusion research.

 

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Does OIM have a functioning brain?

 

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He makes Dwayne DL Dralon sound smart.
If they do get a space elevator, they will need an elevator man.
Perfect for it.

 

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I wish Japan the best with this noble endeavor!

 

The cable would be at least 35000 km long with its center of mass in geostationary orbit, and only the first 10 km or so would experience any significant force from wind. You can calculate how much hurricane-force wind would affect the cable, and the answer is "not much."

 

You would only get thousands of km of cable falling back to earth if your "pissed off muslims" managed to cut the cable thousands of km up. If they hit it with a plane, the plane would only be a few tens of km up at most, and so only a few tens of km of cable would land. Note that this wouldn't destroy the elevator, because the entire elevator system is in a stable orbit - you simply replace the last few km near the ground and you're up and running again. The rest of the cable will just hang there waiting for you to repair it. The falling cable isn't a danger, because its terminal velocity would be very low. Even if it broke very high up and many thousands of km of cable fell back to earth, it would mainly just be a problem of cleaning up all the loose cable. It's not like there would be any fiery destruction.

 

You are right, the icing is much bigger problem. There will be NEVER space elevators....

 

So no possibility of it causing the orbiting satellite to start a descending orbit resulting in the release of the total amount of cable would exist? How about if they purposely stalled the aircraft into a nose up position just before striking the cable at an almost totally stalled air speed? "Low terminal velocity"? Explain that term to me please. I understand fully what "Terminal velocity" is. I don't have a clue what you mean by "Low" Terminal velocity. It seems you're saying that if I reach the highest altitude of an airliner and shove a million kg of this cable out of it, that it would fall harmlessly onto the planet without harming anything? Please explain the math behind that concept. I believe that while "cleaning up all the loose cable", they would have the nasty job of wiping a few thousand people parts from it in the process. Picture this happening over the island of Japan, a very, very populated piece of land at high noon, Japan time.

 

If thee structural strength of materials can't handle making a space elevator, why not make one out of light?
http://en.wikipedia.org/wiki/Beam-powered_propulsion

Draw back: It would require a laser or maser array capable of beaming out 60 GW, once the atmosphere gets to thin the spaceship will need a fuel (H2, Liquefied Air or H2O will do), still launch cost would be many fold lower than todays rockets.

 

Correct. The orbiting satellite, if you use an elevator design that has one (you can also just use a really long cable and not bother with the satellite), is in a stable position beyond geostationary orbit. Cutting the cable would not cause it to fall. In fact, it would cause it to raise very slightly because it now has slightly less mass of the cable pulling down on it.

The force needed to break the cable will be FAR less than the force needed to jerk the satellite down like that. The cable will simply break. A cable strong enough to tug the satellite down would require fantasy technology.

Carbon nanotubes have a relatively low density, so the air resistance as they fall would prevent the cable from gaining enough speed to be very damaging when it hits the ground. Simulations indicate that the terminal velocity would be below 10 m/sec when it hits the ground. Note that this is only relevant if you're talking about a break pretty high up the cable. If the cable breaks within the first few thousand km of the ground it will simply fall "strait down" and only land around the elevator base.

 

Nasor: Correct. The orbiting satellite, if you use an elevator design that has one (you can also just use a really long cable and not bother with the satellite), is in a stable position beyond geostationary orbit.

The upper end of the cables would have to be attached to something. That "something" would be a satellite. How can you say a satellite wouldn't be necessary? Are the cables to just terminate in space?

Cutting the cable would not cause it to fall. In fact, it would cause it to raise very slightly because it now has slightly less mass of the cable pulling down on it.

A very slight adjustment to the attitude of the satellite would result in it's shifting orbit either towards or away from the planet. Automatic adjustment of the satellite would be as necessary as it it with any other orbiting object. If the impact to it's trajectory was sufficient, the orbit could alter enough to cause either release of the cables or a catastrophic degradation to it's orbit. How could this be anything else? You keep referring to "cutting" the cable. How about if the cable is not cut, but moved with enough force to transmit that force to either end of the structure? The kinetic energy would have to dissipate in some manner. That dissipating energy could very well be the force that causes an attitude alteration to the satellite, possibly causing it to change orbit and enter the atmosphere in an uncontrollable decent.

The force needed to break the cable will be FAR less than the force needed to jerk the satellite down like that. The cable will simply break. A cable strong enough to tug the satellite down would require fantasy technology.

Ahhhhh, "fantasy technology". Exactly the case with this entire project. Thank you. My proposed "fantasy technology" is no more unlikely than is yours.

Carbon nanotubes have a relatively low density, so the air resistance as they fall would prevent the cable from gaining enough speed to be very damaging when it hits the ground. Simulations indicate that the terminal velocity would be below 10 m/sec when it hits the ground.

If I throw a 100 kg of anything at you at 10 m/sec, the impact will harm you and possibly kill you. Imagine this at one million kg. falling on a crowded street in downtown Tokoyo.

Note that this is only relevant if you're talking about a break pretty high up the cable. If the cable breaks within the first few thousand km of the ground it will simply fall "strait down" and only land around the elevator base.

Once the cable is free of the satellite, it will be subject to the natural forces of the atmosphere and planetary movement. It would absolutely NOT fall strait down. Even if those forces were not a consideration, an object of that mass and configuration can not and would not gather at a single, stacked neatly, pile at the exact location below it. That, my friend is fantasy math. Plus, again you refer to only the possibility of a break in the cable. That is only one possible outcome of impact to the structure.

 

Yes, the cables could just terminate in space. The only important thing is for the center of mass to be at the point of geostationary orbit. If you use 70k km of cable instead of 35k (half below GEO and half above) then the center of mass would still be at GEO and the system would still be stable. The advantage of this is that the end of the cable would be traveling at far above orbital velocity, so you could launch things directly out into the solar system without having to burn rocket fuel to move from a geostationary orbit to an earth-escape orbit. The disadvantage is that you have to make twice as much cable.

Well, it depends on whether by "fantasy technology" you mean "technology that we have a good idea how to build and is probably a few years or decades away" or if you want it to mean "technology that we have absolutely no clue how to build and probably won't develop for the foreseeable future."

The minimum strength for a space elevator cable is around 65 GPa, but most designs call for a cable material with a strength of around 120-130 GPa so that there's a comfortable safety factor. We have already developed carbon nanotubes with measured tensile strengths of 63 GPa, and calculations indicate that "ideal" nanotube ropes should have tensile strengths around 300 GPa. So we know of a material that's strong enough, and we are getting progressively better and better at making it. Of course it's not clear exactly when 100+ GPa nanotube cables that are appropriate for a space elevator will be developed, but it's definitely a technology that everyone expects within a decade or two - we aren't talking about wacky fantasy technology that we have no idea how to build.

A cable that would let you pull the entire assembly down from orbit without breaking would have to be a LOT stronger than a cable that merely hung under its own weight.

The cable will have a density of about 1.3 g/cm^3, and is less than 1 cm thick along most of its length, so no one is ever likely to be hit with 100 kg of it. A better analogy would be having two airplanes flying over Tokyo with a long, thin piece of nylon rope strung out between them. Then they cut the rope loose. The rope isn't going to crush anyone or damage any buildings when it lands, it's just going to drape itself over the city and annoy people.

On a side note, Tokyo would never be hit with the cable anyway because the cable has to be anchored along the equator. Sorry, no space elevator for Japan.

You are forgetting that entire cable is already rotating exactly in sync with the surface of the earth when it is cut. Yes, of course eventually coriolis forces will cause it to "wrap around" the earth, but the cut would have to be extremely high (thousands of km up) before they had any significant effect. Of course the cable isn't going to coil itself into a nice little pile right at the base of the elevator, it's going to be subject to wind etc. as it floats down to earth. The point is that there isn't going to be any significant "wrapping" of the cable around the earth unless the cut is made very high.

Edit: And if you're still really worried about it, you can anchor the cable on a ship over the ocean or something.

As for problems that don't break the cable, one of the nice things about the space elevator is that it is self-stabilizing because of the earth's rotation and the centripetal force being exerted on the portion of the elevator system that's beyond geostationary orbit. If you simply pull on the cable for a while it will deform the cable slightly and pull the whole thing down a little, but as soon as you release the pressure it will begin to drift back to its original position. This is pretty important, because otherwise the whole thing would eventually become destabilized by the changes in angular momentum that occur when cars move up or down it.

NGM, you seem very hostile to the idea of a space elevator. It's perfectly fine that you're skeptical, and there are indeed many major engineering challenges associated with building one. But you might want to remember that a lot of serious physicists and engineers have evaluated the idea and they generally agree that it will be feasible relatively soon. It's not like this is some wild idea that a crackpot came up with on this message board; space elevators have been seriously studied since the 1970s. You've only been hearing about them in the popular press recently because it has only been in the last 10 years or so that we've gotten close to having the technology to actually make a cable that is strong enough. Of course that doesn't mean that we will necessarily ever be able to build one, but most of the things that immediately come to mind as potential problems have already been very thoroughly evaluated by professionals.

 

Also, I just did a little googling and it appears that the experts all agree that a carbon nanotube cable would mostly burn up on reentry anyway...so no worries there.

 

Wouldn't the cable need some tension on it in order to support the weight of the ascent vehicle? So, if it broke, it would lift out into a higher orbit.

 

Nasor: NGM, you seem very hostile to the idea of a space elevator. It's perfectly fine that you're skeptical, and there are indeed many major engineering challenges associated with building one. But you might want to remember that a lot of serious physicists and engineers have evaluated the idea and they generally agree that it will be feasible relatively soon. It's not like this is some wild idea that a crackpot came up with on this message board; space elevators have been seriously studied since the 1970s. You've only been hearing about them in the popular press recently because it has only been in the last 10 years or so that we've gotten close to having the technology to actually make a cable that is strong enough. Of course that doesn't mean that we will necessarily ever be able to build one, but most of the things that immediately come to mind as potential problems have already been very thoroughly evaluated by professionals.

I've moved your last series of comments to the front so as to address them first.

I certainly don't mean to appear hostile. I'm anything but hostile to the idea or any idea that furthers any type of scientific progress. However, I am supplying argument to the theory. That's a healthy process and should be encouraged, not discouraged or seen as an attack. Of the potential problems that have been addressed, what of a simple hurricane? They happen often in Japan. The costs involved with replacement of the downed cables would become too much to bear if done every season.

Yes, the cables could just terminate in space. The only important thing is for the center of mass to be at the point of geostationary orbit. If you use 70k km of cable instead of 35k (half below GEO and half above) then the center of mass would still be at GEO and the system would still be stable. The advantage of this is that the end of the cable would be traveling at far above orbital velocity, so you could launch things directly out into the solar system without having to burn rocket fuel to move from a geostationary orbit to an earth-escape orbit. The disadvantage is that you have to make twice as much cable.

In a perfect, non-trashed atmosphere and orbit, I could see it working. It's a sound theory with sound math. However, I don't believe that all the variables are being considered and when those variables are considered, it'll make the project pointless in practice. I would have to see a simulation work with those variables randomly assigned and dealt with, prior to my acceptance of this as a viable method.

Well, it depends on whether by "fantasy technology" you mean "technology that we have a good idea how to build and is probably a few years or decades away" or if you want it to mean "technology that we have absolutely no clue how to build and probably won't develop for the foreseeable future."

I eagerly await the development of the science and it's successful testing. Until then, I'm very, very sceptical of it's future in this context.

The minimum strength for a space elevator cable is around 65 GPa, but most designs call for a cable material with a strength of around 120-130 GPa so that there's a comfortable safety factor. We have already developed carbon nanotubes with measured tensile strengths of 63 GPa, and calculations indicate that "ideal" nanotube ropes should have tensile strengths around 300 GPa. So we know of a material that's strong enough, and we are getting progressively better and better at making it. Of course it's not clear exactly when 100+ GPa nanotube cables that are appropriate for a space elevator will be developed, but it's definitely a technology that everyone expects within a decade or two - we aren't talking about wacky fantasy technology that we have no idea how to build.

The random and combined kinetic energy of one very small hurricane would defeat it. How could it not be so?

The cable will have a density of about 1.3 g/cm^3, and is less than 1 cm thick along most of its length, so no one is ever likely to be hit with 100 kg of it. A better analogy would be having two airplanes flying over Tokyo with a long, thin piece of nylon rope strung out between them. Then they cut the rope loose. The rope isn't going to crush anyone or damage any buildings when it lands, it's just going to drape itself over the city.

And the cost of replacing this cable every time it is broken by nature or man? How long to build? How long to replace? I don't believe it's feasible until some sort of "protection" could be installed around it that prevented it's damage. That is the part of the technology I'm not seeing yet. The perfect world scenario only works in a lab setting. In the actual implementation of experiment, it seldom occurs for more than a fraction of time.

You are forgetting that entire cable is already rotating exactly in sync with the surface of the earth when it is cut. Yes, of course eventually coriolis forces will cause it to "wrap around" the earth, but the cut would have to be extremely high (thousands of km up) before they had any significant effect. Of course the cable isn't going to coil itself into a nice little pile right at the base of the elevator, it's going to be subject to wind etc. as it floats down to earth. The point is that there isn't going to be any significant "wrapping" of the cable around the earth unless the cut is made very high.

Edit: And if you're still really worried about it, you can anchor the cable on a ship over the ocean or something.

As for problems that don't break the cable, one of the nice things about the space elevator is that it is self-stabilizing because of the earth's rotation and the centripetal force being exerted on the portion of the elevator system that's beyond geostationary orbit. If you simply pull on the cable for a while it will deform the cable slightly and pull the whole thing down a little, but as soon as you release the pressure it will begin to drift back to its original position. This is pretty important, because otherwise the whole thing would eventually become destabilized by the changes in angular momentum that occur when cars move up or down it.

I've found in reality that re-establishing an exact place in space is almost impossible. Each time one force or another was exerted upon the system, it would result in something having to re-establish that exact place in space. To allow anything other would be inviting disaster as a result of accumulated stress and would be impossible to contain in any precise manner.

Do you understand my question to this? It's not a structural question where each item of structure is in question. I trust the math and science behind the invention. It's the practice of the implementation with consideration of every conceivable variable that is likely to happen to a structure of this magnitude that I have my doubts about. This is what I believe are the restricting facets of the problem as it exists right at this moment. These hurdles must be addressed and overcome before any real consideration is given to implementation of this theory outside of a lab environment.

Thank you for this discussion. It was enlightening and interesting. Your knowledge of the subject matter is obviously a result of interest. We seem to have reached a point in which it's pointless to continue until further science is developed that will enable us to cast aside the current problems facing it's actual implementation.

 

In most designs the cable isn't kept tense, so as the ascent vehicle ascends it does indeed bend the cable and pull the anchoring satellite out of position. But since the system is self-stabilizing, it will all drift back into position once the car reaches the top.

 

The tension would be supplied by the very mass of it's own structure and it's ability to absorb stress throughout it's mass. Radical stress is my only concern. Too many possibilities exist that would provide it and cause catastrophic damage the the structure.

 

forgive me folks, I haven't eaten today and it's after 1630 hrs here. I'm starving. I hate to leave while everyone is online, but my stomach drives me!

I'll catch up later if possible.

Nat

 

Japan could never actually build this thing in Japan, because they can only be built over the equator. You can't have a geostationary orbit over Japan, sadly.

 

Also, with existing elevator technology (albeit being Japanese already) it would take nearly two months to get to the terminus of the elevator.