Space elevator

halfway, not hallway

mumble, mumble

The relevance is that constantly throughout history there are naysayers. And constantly they are wrong. Currently there is no hard evidence to say is it completely possible or impossible. I support the concept of a space elevator, but I don’t think that its creation is inevitable. By the same token, anyone saying that there is a 1:1 chance that any idea is completely impossible is most likely kidding themselves.

Assuming this is a response to my question, you’re confused. Most of us understand centripetal force. What you’re not addressing is this: if you swing a heavy weight on the end of a rope and simultaneously let the rope out, the rotation will actually slow unless you provide additional angular force.

Besides, the swinging bucket analogy completely misses the main gist of a space elevator, which relies on the concept of geosynchronous orbit.

Sounds interesting, but it needs a better name: the skyhook!

I think the mass of each payload ends up being negligible compared to the mass of the elevator structure, so there’s no significant tilting of the elevator. The cumulative effect of sending a payload every day can be cancelled by some type of rocket engine mounted somewhere along the elevator, or by sending down as much mass as you send up.

The famous nay-sayers, the ones you know, are those who ultimately ended up wrong. The ones who were right are mentioned much less in history, like the people who said you would never be able to turn lead into gold, or go faster than light, or perform telekenesis. It is much easier to ignore someone who said there was a limit to what humans could do who ended up right than someone who did the same but was proved incorrect by a spectacle of scientific innovation. It is simply irrational to characterize all nay-sayers as constantly “wrong”, to say nothing myself on the possibility of building this space elevator contraption.

I’m no mathematician, but I believe the folks who’ve said it could be done.

I simply question whether it SHOULD be done. Particularly after 9/11. I mean, talk about a target for loony people…

So what are you saying, Wang? That we should tear down every potential target for terrorists? Impossible and absurd. If they didn’t have the WTC as a target on 9/11, they would have found something else (wasn’t the selected target for the plane that hit the Pentagon originally the White House?). If terrorists did manage to hijack a plane (and really do you think that in a post 9/11 people are simply going to allow hijackers to take over a plane?) they’d find the space elevator to be well guarded. A space elevator drops the price of putting something in orbit to 1/10th what it is now. To put it in simplier terms: the military can put up more satellites than they are now, for the same amount of money. Do you think that the military is going to allow a gravy train like a space elevator to be a sitting duck for a bunch of nutbags in a hijacked jetliner? Not on your life. You’d have an easier time killing the President than you would taking that thing out. (And despite the Bush Admins claims to the contrary, I think that the terrorists have shot their wad, and they’ll never be able to pull off such a big stunt again.)

Extraordinary claims require extraordinary proof. A space elevator certainly falls into this category. I have yet to see anything close to even a half baked proof of concept let alone an extraordinary proof.

I can’t even get anything at all sensical to my standard question in these threads: What is the state of the entire system 1 hour before final hookup?

Nanotubes are 2 orders of magnitude from being strong enough to maintain a space elevator in a stable configuration. And since it won’t be stable…

To claim space elvators are impossible requires equally extraordinary proof. Until someone does enough research to determine the feasibility of the concept, both claims (“possible” vs. “impossible”) should be considered unproven.

Just a long cable hanging down from the geosynchronous orbit. The cable is under tension, held taut by gravity (or tidal force, depending on how you think about it). Such a structure should be stable at any length, even 1 meter short of reaching the earth’s surface.

Some people think otherwise. Do you have any reason to believe that the naysayers’ analyses are more sound?

Well, I have some extraordinary questions that need answering before anyone can put up a Space Elevator.

First someone said that the reaction forces of any amount of mass that is sent up the elevator can be countered by sending some amount of mass down. This idea is great except for the reaction forces created when we send the counter weight up. Including rockets seems like a plausible solution, but there are other issues there. Like refueling the rockets, what kind of tension will they create?

Second and more important. All orbits are elliptical. Even a geosyncronous orbit is elliptical. Will the cable stretch to allow an elliptical orbit? Will a cable reservoir be attached to the platform where it meets the earth?

Lastly, even if it is a geosyncronous orbit, wouldn’t the cable experience superheating in the 20-30 mile length because of air friction? Air is not a still medium to be sure, but the cable is still rotating through this medium at suborbital speeds, hence there should be some heating right?

How would people work out these issues?

The counterweights shouldn’t go back up. The mass sent down should take the form of returning passengers, imports and if necessary, ballast (rocks). Construction of a space elevator would require raw material obtained from asteroids or comets, so obtaining ballast shouldn’t be a problem.

The orbit needs to be a geostationary orbit, which is perfectly circular. A circle is an ellipse.

No, the entire structure is stationary relative to the earth. The elevator is one big satellite in geostationary orbit - it’s so big that the tip of it reaches the earth’s surface, even though the center of mass is 36,000 km away. There is no significant motion between the air and the structure, just the intrinsic speed of the wind.

This holds true even during construction; the elevator starts out as a small geostationary satellite and gradually grows longer until it reaches the earth’s surface. At all stages of construction the entire structure is fixed relative to the earth, and is self-supporting (kept under tension by the earth’s tidal force).

Huh? Are you talking about during construction or when the elevator’s in operation? If you’re talking about during construction, there’s no need to send the counterweights up the elevator (and probably no way to). You’ll just send them up using a Delta II (or whatever rocket’s being used at that time) like the rest of the components were sent up. If you’re talking about when the elevator’s in operation, it won’t be necessary to send the counterweights down [i[every* time. Once a cheap way is found to put things into space, you can expect a lot of manufacturing processes to move into space.

Why? Because you can make things in zero gravity environments better than you can here on Earth. For example: All Earth-made ball bearings have minute flat spots in them because there’s no way to completely eliminate them on Earth. Bearings made in zero gravity will be perfectly round, these bearings will thus have a lower friction level than those made on Earth. (So the clever high-end manufacturers of things that use ball-bearings will scarf them up so that they can claim longer life and lower friction levels in their gear.) Another example are things made on lathes, they sag slightly under the weight of gravity. On your run of the mill things the sag isn’t worth worrying about, but on precision equipment it is something that has to be compensated for. Make those things in zero gravity, and you don’t have to worry about it.

This doesn’t mean that a week after the elevator goes up, you’ll start seeing things with a “Made in Space” label on them. The first things that will be built up there will be scientific gear and machine tools. After that will come components (if not the actual things) for high-end stuff like really expensive cars and electronics. Perhaps within 20 to 30 years after the thing’s built, you’ll see stuff made in space that the average consumer can afford to buy.

I won’t even bother to discuss things which in theory could be made in a zero gravity environment that can’t be made on Earth, simply because we’ve no real idea what they are, and no matter how many I could name, or what their properties might be the real number and characteristics will turn out to be different than anything we’ve thought of.


Actually, the cable reservoir would most likely be in orbit with the rest of the elevator.


Wrong. Geosynchronous orbit means that the top of the elevator will be over the exact same spot on the Earth (within a few feet or so) 24 hours a day. It will be travelling at the same speed as the air surrounding the cable. So there won’t be any friction created because the cable and the air will be travelling at the same speeds. (Not entirely accurate, of course, but the difference in the speed of the wind and the cable would be the same as that of a low-level wind against an ordinary building.)

Minor nitpick: You ** can ** turn lead into gold, and other sorts of transmutations. Of course, you need a partical accelerator and so much energy that is cost more to make gold out of other elements than it does to simply dig the gold out of the ground. Still, it can be done.

Have you actually bothered to read any of the actual design studies people have pointed you to?

1 hour before final hookup, the cable is still (slowly) unreeling. The lower cable end (with a weight attached to keep it under tension) is descending through the atmosphere, somewhere near the final hookup point. You will probably need to use a helicopter or something similar to catch it and guide it to the hookup point. The reel is at the top end of the cable, well above geosyncronous point. The center of gravity of the entire system is still in geosyncronous orbit, so it’s still stable; you could stop the unreeling and let the system just sit, dangling there, although wind might push the lower end around a bit.

At the moment of hookup, there is zero tension on the attachment point. After attachment you’ll unreel a bit more of the cable, which will bring the center of gravity of the system slightly above the geosynchronous point, ensuring continous tension on the cable.

Wrong, and still shows you don’t even understand how a space elevator is supposed to work. Technically speaking, you could build a space elevator with ordinary steel, although the degree of taper and hence the amount of material would be astronomical. For a reasonable mass and amount of taper, you want materials with a tensile strength of about 62 GPa. If you disagree with this, show your math as to why this isn’t so… Currently available composite materials can get to 20 GPa, which is well within an order of magnitude of the needed strength. Carbon nanotubes have an estimated tensile strength of 200 GPa - way more than enough.

You have had this explained to you multiple times. You have responded with nothing more than bluster. I think you are the one who needs to back up your claims with evidence here.

The proposals I’ve seen don’t include moving a counterwight down as you lift mass. If you add mass to the upper end of the cable after attachment, or simply extend the upper end by unreeling a bit more cable, the entire assembly will be under constant tension. The center of gravity of this kind of tether will be slightly above the geosynchronous point. Above geosynchronous point, orbital velocity will have a sattelite normally orbiting slower than once per day. The cable system will be going slightly faster than orbital velocity, so it will want to gain altitude, but the attachment point to the earth prevents it from doing so. So the entire cable will be under tension. Small masses can be lifted up the cable without pulling it down, so long as the mass is not large enough or accelerating upwards quickly enough to pull the cable system’s center of mass below geosynchronous point.

The cable is anchored strongly to a point on the earth’s equater, probably on an ocean platform. The attachment point is under constant tension. Once attached and tensioned it’s not behaving as a fewwly orbiting satellite anymore.

The starting point for the cable, the place where you put the reel when you start, is in geosynchronous orbit; it always stays over the same spot on the earth’s surface. It’s not stationary, but the orbit it occupies has a period of once per day, so someone standing on the ground will always see it in the same spot in the sky. When the cable is attached, someone on the ground will see it as an unmoving line going from a fixed spot on the ground to a fixed spot on the sky. It’s not moving with respect to the point on the ground where it attaches, or the atmosphere it’s sticking through, so there’s no relative velocity to cause any heating.

I think the major problem with the space elevator would be the Coriolis acceleration.
A geostationary orbit means that the angular velocity of both ends is the same. But since the radius is different, it means that the tangential velocities are quite different. A body leaving the Earth’s surface has it’s tangential velocity 410^7/(2460*60) m/s. The valocity at the upper end is bigger, so the body must be accelerated. This acceleration is provided by the cables. In the percourse from the upper to the lower end we have the inverse phenomenon.
The cables are supposed to support their proper weight and that of the load, but are they capable of sustaining the lateral force?

If the cable tension is insifficient to provide the lateral force it can be easily supplemented by rocket engines and/or counterweights, as I tried to explain above.

It seems to me that the biggest long term problem for an orbital elevator is not the elevator itself but the environment: the ground station will move due to continental drift. Not by much, mind you, but even a small movement will engender massive forces. And then there’s earthquakes. If you have it floating just above the surface (which it can due to the counterweight), then your problem becomes the wind - think of it as a giant guitar string.

We’ll find solutions and get there eventually.

What about the shadow that this thing is going to cast? How big is that going to be? And what’s going to happen to those areas which lie in the shadow?