How to build a space elevator?

[Mokele]

Ok, so, I'm presuming everyone is familiar with space elevators, as they've been discussed here plenty of times, so I thought I'd pose a special challenge.

 

Imagine we have all the parts - we have the ground station, the satellite, the elevator, and the super-strong cable.

 

How do you put it all together?

[Xittenn]

With a space crane..........................................we could call it skyhook. That's my final answer. ummmmmmmmmmmmmmmmmmmmm damn. You would most definitely have to manufacture the cable in space either introducing the materials one load at a time or finding the materials up there somewhere. The cable would then have to be introduced into earths atmosphere under seriously controlled descent..................

[iNow]

I think it would be done similar to building a bridge. When we build bridges, we do construction on both sides, and then couple those sides somehow once basic foundations and supporting structures are in place on each side. Same here with the space elevator. We build some on the ground, we build some in space, then we couple them.

 

Readers should please note that I pulled the above idea out of a colonic region and it may not be valid at all.

[Mokele]

But how to couple them? Feed the cable up from the ground? Down from space? The former has problems with supporting it as you move it up, while the latter has problems with air resistance and shifting the satellite's center of gravity.

[D H]

The center of mass of the space elevator must be at geosynchronous altitude. The final configuration will be a cable that extends well beyond geosynchronous altitude. One very long cable would do the trick. The cable length can be decreased significantly by using a countermass at the far end.

 

So, how to build it? Let's assume we have a smallish (not very thick) elevator in place. We can beef this structure up by sending climbers up the elevator that reel out additional cable as they climb. We have to start small (the original cable isn't all that strong), but eventually the cable can be built up from a small seed.

 

So how to build this seed elevator: Simple: Reel it out from geosychronous altitude. The trick is to reel out two cables. One cable will descend to Earth while the other cable will go "up". Gravity gradient will naturally keep the entire cable in a vertical orientation. When the Earth end reaches the surface, anchor it to the Earth. Voila! Space elevator.

 

Too much hand-waving (far too much for me, at least). There are problems with atmosphere. The Earth's atmosphere super-rotates at high altitudes. At 200 km, the atmospheric rotation rate is 1.1 rotations per day. At 350 km, its about 1.4 rotations per day. (From there the rotation rate starts decreasing.) The descending cable will start feeling this super-rotational wind well above 350 km.

 

Another problem: Carbon nanotubes are excellent conductors of electricity. The spark that will jump from the cable end to the Earth as the cable approaches the surface of the Earth will not just be a little tiny spark. It will be a bolt of lightning and then some.

 

Yet another problem: Part of the cable will permanently be in the Van Allen belts. I suspect the radiation damage to the cable in that area will be significant. Will the degradation occur faster than we can repair it?

[cameron marical]

wouldnt just one small tug on this cable send the satellite crashing down back to earth?

[D H]

What satellite?

[chrisman10]

Sir, do you have a source for this. Please post the link here.

[iNow]

Chris - Please clarify to whom you are speaking and for what assertion you would like a reference. It was unclear since you did not quote anyone or anything. Thanks.

[Xittenn]

Stepping out there as I so love to do.......is there any proposals on any form of energy cable. I'm thinking not an insulated tube filled with ionized Argon magnetically creating tensile strength but something that might actually work.................. maybe even as to suplement tensile capacity.

[D H]

The center of mass of the space elevator must be at geosynchronous altitude.

My bad. This is not correct. The center of gravity of the space elevator must be at geosynchronous altitude. Center of mass and center of gravity are not the same thing, particularly so when the structure is seven+ earth diameters tall. The center of gravity is the point at which the gravitational force is equal to the total gravitational force on the

 

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Sir, do you have a source for this. Please post the link here.

 

I'll assume you are talking about me. Hard to tell, since you didn't qualify "sir" or "this".

 

The final configuration will be a cable that extends well beyond geosynchronous altitude.

This should be pretty obvious. If you need a reference for this, use google.

 

So, how to build it? Let's assume we have a smallish (not very thick) elevator in place. We can beef this structure up by sending climbers up the elevator that reel out additional cable as they climb. We have to start small (the original cable isn't all that strong), but eventually the cable can be built up from a small seed.

 

So how to build this seed elevator: Simple: Reel it out from geosychronous altitude. The trick is to reel out two cables. One cable will descend to Earth while the other cable will go "up". Gravity gradient will naturally keep the entire cable in a vertical orientation. When the Earth end reaches the surface, anchor it to the Earth. Voila! Space elevator.

This is pretty standard fare. Google is your friend.

 

The Earth's atmosphere super-rotates at high altitudes. At 200 km, the atmospheric rotation rate is 1.1 rotations per day. At 350 km, its about 1.4 rotations per day. (From there the rotation rate starts decreasing.)

Pretty standard fare for an aeronautical engineer who models atmospheric drag. For anyone else,

 

Walker, D.M.C., "Upper-atmosphere rotation rate from analysis of the orbital inclination of Explorer", http://adsabs.harvard.edu/abs/1975uarr.rept.....W

 

King-Hele, D.G., "Decrease in Upper-atmosphere Rotation Rate at Heights above 350 km", Nature 233, 325 - 326 (1971). http://www.nature.com/nature/journal/v233/n5318/abs/233325a0.html

[moth]

could you build the cable factory in geosynchronous orbit and feed the cable out in that orbit as it was created and when it was long enough to reach the surface, electrostatic forces could be used to pull the ground end down through the atmosphere?

http://en.wikipedia.org/wiki/Electrodynamic_tether

Edited February 4, 2009 by moth
added link

[cameron marical]

when i said sattelite, i meant whatever the cable would be attached to that is in space. like the space elavator.

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and again, wouldnt it just fall out of space and come crashing down to earth?

[D H]

and again, wouldnt it just fall out of space and come crashing down to earth?

No. What makes you think it would?

[iNow]

No. What makes you think it would?

 

Probably the lack of resistance out in space. If two objects in space were tethered together, and you gave a tug to one of them, then the other would jerk toward the tug to some degree no matter how massive it was. I presume that CM is applying the same logic, thinking that the side of the elevator in space lacks resistance, so any tugs to the tether from the earth side would cause its orbit to destablize and the object to come falling toward the surface.

 

I think he is looking for an explanation in simple terms of why this would NOT happen.

[SH3RL0CK]

Couldn't the rotation of the earth provide momentum to the satellite?

 

The way I see it, both ends should be going around the earth in exactly one day. The energy lost by pulling something up would cause the satellite end to drop to a lower (faster) orbit. But then the cable will hold the satelite in place at that orbit (1 day rotation) because the cable is tied to earth. The rotation of the earth would pull the satellite end back into geostationary alignment since this is the speed the satellite end would trail the earth end. Please someone correct me if I am wrong about this.

 

Would there be a limit to the rate of sending stuff up such that the rotation of the earth wouldn't do this? Maybe when the cable would break?

[D H]

The upper end of the space elevator is far above geosychronous altitude. It has to be as the center of gravity of the entire elevator structure (the entire cable plus the counterbalance) has to be at geosynchronous altitude.

[Mokele]

Actually, the issue of "tugging on the line" is something I've considered. Remember, the tether is going to be subject to some pretty insane wind forces, which could result in unwanted motion of the satellite and stress on the whole structure.

 

Would it be better to have the CoG above geosynchronous, to put more tension on the tether and hopefully resist disturbances?

[D H]

Would it be better to have the CoG above geosynchronous, to put more tension on the tether and hopefully resist disturbances?

Do you want to kill millions of people? The center of gravity must be at geosychronous altitude. Suppose the CoG migrates to tens of thousands of kilometers above geosynchronous altitude. The elevator structure will thus rotate at less than one revolution per day. The cable will lean to the west. Once it becomes horizontal, the Earth will start reeling the cable in. The process will stop when either the cable breaks or the Earth has reeled in enough cable to make the CoG be at the geosynchronous point.

[Mokele]

Do you want to kill millions of people?

 

Hey, everyone needs a hobby.

 

Suppose the CoG migrates to tens of thousands of kilometers above geosynchronous altitude. The elevator structure will thus rotate at less than one revolution per day. The cable will lean to the west.

 

Ahh, I was thinking more along the lines of having the CoG tens of meters, or maybe just ten meters, above geosynchronous altitude. Just enough to keep a little bit of tension in the line, but not enough to really have a huge effect on orbit.

[Xittenn]

 

So, how to build it? Let's assume we have a smallish (not very thick) elevator in place. We can beef this structure up by sending climbers up the elevator that reel out additional cable as they climb. We have to start small (the original cable isn't all that strong), but eventually the cable can be built up from a small seed.

 

So how to build this seed elevator: Simple: Reel it out from geosychronous altitude. The trick is to reel out two cables. One cable will descend to Earth while the other cable will go "up". Gravity gradient will naturally keep the entire cable in a vertical orientation. When the Earth end reaches the surface, anchor it to the Earth. Voila! Space elevator.

 

 

I like the idea of building off of a seed cable. I was thinking though, oh oh, most cables are either wound into a helical pattern or, as are many elevator cables, fused by a rubber composite into a flat band. Neither of these are really feasible in your seed method. Proposals? Maybe I'm missing something..........

[Phi for All]

New information for an old topic:

 

http://news.yahoo.com/japanese-company-proposes-space-elevator-2050-215100396.html

 

We could see this in our lifetime. Unless some kid pushes the buttons for EVERY floor. That could take forever.

[slavenenco]

Does anyone now what kind of materials they would use?

[PaulS1950]

Carbon nano-tube for the cable, light-weight materials for the elevator to reduce the load on the lift mechanism but strong enough for close to one atmosphere of pressure. Remember that it would have to be at least as big as the shuttle bay and have food, water, and air for the two week trip. The hurdle that needs to be jumped is production and assembly of enough nano-tubes to make a cable big enough and long enough to reach to a geo-synchronous satelite.

 

Paul

[Xittenn]

I still think this is going to require something a little more sophisticated than carbon nano-tubes. I should make a 3D animated proposal for the seeding process, but I won't 'cause I don't have the time, so I will not imply that this might ever happen; I still need to do the math on the damn Darrieus Windmill. But I have a few ideas where all I'm seeing on this is a lineup of partial statements . . . . we are going to even though we still have nothing. I'm not included in that we! : )