Space Elevators

[imported_Hamzter]

Pump N2 around a superconducting cable? Can you imagine how heavy all the piping would be? And how would you go about pumping it all there in the first place?

A really HTSC would be a bit more feasable, but it would add thousands of tons to the weight of the structure that isn't really neccesary, when nuclear or transmitted power are available.

On the note of power, is power transmission feasable (microwave or laser beam)? I'd imagine it wouldn't be much use in the atmosphere, due to beam absorption. However, it could be transmitted from a station at geosynchronous orbit loaded with solar panels when the climber is above 100km or so. It'd probably be fairly difficult to focus the beam correctly when you're aiming at a target <10m across from 36,000km away. At all possible? If not, I'm sure nuclear power could be used if we got past the political issues.

 

[Howard]

Originally posted by: Hamzter
Pump N2 around a superconducting cable? Can you imagine how heavy all the piping would be? And how would you go about pumping it all there in the first place?

A really HTSC would be a bit more feasable, but it would add thousands of tons to the weight of the structure that isn't really neccesary, when nuclear or transmitted power are available.

Keep it cold enough and the sheathing won't have to be terribly strong. Silica aerogel is as close as you can get to a vacuum (re: its thermal conductivity), and it's very, very light. Ideal material to keep it cold.

 

[imported_Hamzter]

Say again? What's the sheathing you're talking about? A superconducting cable would only be at all feasable if no cooling equipment was required, meaning it has to operate at the temperatures the cable would experience. Even if a superconducter is invented that can handle the conditions is found, it would add a huge ammount of weight to the cable.

 

[Calin]

A superconductor keeps a single temperature along the entire length/surface/volume/whatever. So, it is enough to cool a single end if the thermal losses (well, gains) in the cable are low enough.
However, you won't be able to use normal microwave or laser, as the cable will flex in all directions. You will need a "homing device".
Also, I don't think a laser firing against Earth (even against base station) from the space will be desirable

 

[Armitage]

Originally posted by: Calin
No. You are wrong.
If the object is moving to north or to south (at the same altitude), the Coriolis force will deflect it as you said (on Equator there will be no deflection).
However, if the object is moving up, the Coriolis force will move it to the west, and if it is descending, the force will move it to the east.

Yep - my bad. I did consider this, but didn't think of it as a coriolis force. But a quick look at the equation shows that it is.

 

[Unatae]

Just a quick word on laser usage.
A high power UV laser could indeed be used to ionise the air into a lightning channel. Infact, one of my physics profs made a handheld (single shot, short range) 'phaser/taser' using a VdG for charging, cap and UV lasers he had in his lab. Unfortunatly he had to disasemble it. Damn OHS.
Also, there have already been proposals to power inter-planetary solar-sail based craft via earth based lasers, so this would be a viable means of powering the climbers. If it can track a spacecraft, it can track the climber. Anyway, dont you remember the microwave power plants from simcity? If it worked for them....

 

[unipidity]

But you cant really power a spacecraft using a laser. Even with insanely accurate systems, you are limited by atmospheric distortion. You cannot make a spacecraft that moves outside the isoplanetic angle from some kind of guide star if you are using an AO system. I suppose you could just make your spacecraft stupidly large.

 

[imported_Hamzter]

Originally posted by: Unatae
Anyway, dont you remember the microwave power plants from simcity? If it worked for them....

Lol, I remember them! I also seem to remember they'd cause disasters every so often when the beam missed the dish

Unipidity, I suggested before that the beam was only used above the atmosphere, transmitted from a station at geosychronous orbit, so there's no need to worry about atmospheric distortion. However, after thinking about this problem a bit, I think the accuracy required is simply too high, it's lke trying to hit the head of a pin from a kilometer away with a laser. I also wouldn't like to be stood too near the base of the cable if it happened to miss, you'd end up a bit crispy.

Since nuclear fuel is rather expensive (plus the fact that everyone's scared silly of the stuff), what other fuel options are there? Would you be able to run the thing on a good old combustion engine, keeping in mind you'd have to cart along your own oxidiser aswell?

 

[Calin]

A supposedly existent (At that time) superconductor, with recharging "stations" on the way up (just two electric contacts, or maybe even a coil). Can a big enough alternative current thru a linear wire be enough to "charge" a transformer with the secondary coil on the climber?

 

[Terumo]

In all of these wonderful ideas the problem with maintence is still there. It'll be a technological miracle to be able to maintain that many meters of anything without error.

It's not impossible, but we'll be hit with the cost vs. practicality of the whole issue. Can't just use janitors and everyday electricians to maintain the cable(s). Compound the dangers involved, just trying to keep the cable in working condition would be astronomical in the pocketbook.

It's doable, but the costs are prohibitive (even if private industry would finance such a project).

Flight, ironically, is cheaper to maintain.

 

[ahurtt]

First off. . .they estimate it would have to be between 20K and 40K km long? What kinda estimate is that? That's like the weather man saying, "we might get 2 inches or 20 feet of snow." Second, would a 20,000 or 40,000 km long arm attached to the earth sticking straight up into space not slow down the rotation of the Earth similar to like when a figure skater sticks out their arms and legs while spinning around? And would you need another one on the other side of the earth to serve as a counter balance?
Second, so way we built it, now what? What do you do with it? Just how fast can the climbers traverse its length? Doesn't it already take like 15 or 20 minutes just to take an elevator to the top of the Empire State building?

 

[Looney]

Originally posted by: ahurtt
First off. . .they estimate it would have to be between 20K and 40K km long? What kinda estimate is that? That's like the weather man saying, "we might get 2 inches or 20 feet of snow."

Um that's just the estimate. Once somebody starts building this, they would probably spend some time calculating a more accurate number.

Second, would a 20,000 or 40,000 km long arm attached to the earth sticking straight up into space not slow down the rotation of the Earth similar to like when a figure skater sticks out their arms and legs while spinning around? And would you need another one on the other side of the earth to serve as a counter balance?

No. If a figure skater holds out a string while spinning, is that string going to affect them?

Second, so way we built it, now what? What do you do with it? Just how fast can the climbers traverse its length? Doesn't it already take like 15 or 20 minutes just to take an elevator to the top of the Empire State building?

Maybe like put things into space easier and more efficient? And yes, the ride up would take days.

 

[ahurtt]

Originally posted by: Hardcore

Originally posted by: ahurtt
First off. . .they estimate it would have to be between 20K and 40K km long? What kinda estimate is that? That's like the weather man saying, "we might get 2 inches or 20 feet of snow."

Um that's just the estimate. Once somebody starts building this, they would probably spend some time calculating a more accurate number.

Second, would a 20,000 or 40,000 km long arm attached to the earth sticking straight up into space not slow down the rotation of the Earth similar to like when a figure skater sticks out their arms and legs while spinning around? And would you need another one on the other side of the earth to serve as a counter balance?

No. If a figure skater holds out a string while spinning, is that string going to affect them?

Second, so way we built it, now what? What do you do with it? Just how fast can the climbers traverse its length? Doesn't it already take like 15 or 20 minutes just to take an elevator to the top of the Empire State building?

Maybe like put things into space easier and more efficient? And yes, the ride up would take days.

Ok so maybe a string wouldn't affect a figure skater, but is the ratio of this things weight to the earths weight the same as the ratio of the strings weight to a figure skaters weight? I just don't know and nobody else had seemed to think of this possible question / problem yet. And if the string were long enough, sure it would slow down the skater. What's going to happen if the climber breaks down halfway up there and gets stuck? How do we recover? How much cheaper and more efficient would it really be to have to power this thing and it takes days to get stuff up to space? The space shuttle can get up there much much faster. But we don't really know how much it would cost to shoot something up there on the space elevator at this time I guess.

 

[Armitage]

Originally posted by: ahurtt
First off. . .they estimate it would have to be between 20K and 40K km long? What kinda estimate is that?

The CG of the system has to be at geosynchrounous altitude - about 36000 Km So the 20K estimate is way off. How much longer then 36000 Km depends on the mass of the elevator below 36K and the size of the counterweight you can put together.

That's like the weather man saying, "we might get 2 inches or 20 feet of snow." Second, would a 20,000 or 40,000 km long arm attached to the earth sticking straight up into space not slow down the rotation of the Earth similar to like when a figure skater sticks out their arms and legs while spinning around? And would you need another one on the other side of the earth to serve as a counter balance?

The moment of inertia of the earth is about 8x10^37 Kg/m^2
As a quick WAG, I computed the moment of inertia of of steel rod 0.5 m in diameter and 72000 Km long about its end. That comes out to about 1.9x10^30 Kg/m^2 if I didn't screw it up.

So, 7 order of magnitude down from the MOI of the earth. Pretty small, but I would've thought it it would be smaller actually.

Second, so way we built it, now what? What do you do with it? Just how fast can the climbers traverse its length? Doesn't it already take like 15 or 20 minutes just to take an elevator to the top of the Empire State building?

 

[Jeffyboy]

A hanging cable won't work... the drag of it would send the satellite tumbling to earth. I think people were theorizing an elevator physically connected to earth to bring items up to orbit. Can't imagine myself... would be an incredibly strong tower... not in your lifetime ;-)

 

[Calin]

Why a space elevator? Simply because the efficiency of the space shuttle in putting things in orbit is incredibly low: rocket engines have (quite low) efficiency, they must carry their own oxidizer (which weigh tens of tons or something), and all the speed they gather to get to orbit is lost in reentry.
A theorethical perfect space elevator (with no friction, perfect engines and so on) would use no energy for the carrying cases (the shuttles), only for the masses it puts in orbit - the energy used in climbing would be recovered in descent. A space shuttle must accelerate the entire shuttle and fuel tank to kilometers per second, climb them to altitude, and then the energy is lost as reentry heat.

However, for the moment the space shuttles fly (barely), while the space elevator is just a dream

 

[imported_Hamzter]

Originally posted by: Jeffyboy
A hanging cable won't work... the drag of it would send the satellite tumbling to earth. I think people were theorizing an elevator physically connected to earth to bring items up to orbit. Can't imagine myself... would be an incredibly strong tower... not in your lifetime ;-)

Umm, read the thread, they will work (theoretically anyway), it's already been explained. The cable above geosync would act to hold the bottom part up, so long as your cable's strong enough and the mass about geosync is high enough, it'll work. I imagine people will start actually looking at the concept a bit more seriously in around 50 years, so we may just see one in our lifetimes

 

[Calin]

Too bad they can not make a smaller scale test.

 

[alienal99]

i just had an idea on the power problem of this....what about using solar energy from space and powering the cable from the space-end? This way if the cable is lowered to the earth, the craft that lowers it could be reusable as the power station, as well as a control center for the second half of the cable. If the cable was powered at the start to give whatever we bring out to space enough initial energy to get it to the latter half of the cable, the second power station could then power it from there, and power loss due to resistance in the cable due to the length would be dramatically decreased......to play this even further, what about having a power station every 1000 km or so? Then the use of many shorter range lasers could be used......

alex phillips

 

[Armitage]

Originally posted by: Armitage

Originally posted by: ahurtt
First off. . .they estimate it would have to be between 20K and 40K km long? What kinda estimate is that?

The CG of the system has to be at geosynchrounous altitude - about 36000 Km So the 20K estimate is way off. How much longer then 36000 Km depends on the mass of the elevator below 36K and the size of the counterweight you can put together.

That's like the weather man saying, "we might get 2 inches or 20 feet of snow." Second, would a 20,000 or 40,000 km long arm attached to the earth sticking straight up into space not slow down the rotation of the Earth similar to like when a figure skater sticks out their arms and legs while spinning around? And would you need another one on the other side of the earth to serve as a counter balance?

The moment of inertia of the earth is about 8x10^37 Kg/m^2
As a quick WAG, I computed the moment of inertia of of steel rod 0.5 m in diameter and 72000 Km long about its end. That comes out to about 1.9x10^30 Kg/m^2 if I didn't screw it up.

So, 7 order of magnitude down from the MOI of the earth. Pretty small, but I would've thought it it would be smaller actually.

Second, so way we built it, now what? What do you do with it? Just how fast can the climbers traverse its length? Doesn't it already take like 15 or 20 minutes just to take an elevator to the top of the Empire State building?

Was thinking about this moment of inertia thing a bit more last night, and it's actually irrelevent. The elevator is in orbit about the earth - it isn't being spun by the earth. The figure skater analogy doesn't hold.

 

[JonB]

Just how fast can the climbers traverse its length? Doesn't it already take like 15 or 20 minutes just to take an elevator to the top of the Empire State building?

first, the elevator in the Empire State Building is much faster than that, same for the Sears Tower in Chicago (those are the tallest I've ridden).

Second, speed isn't the main concern. It is cost and reliability. Riding a flaming booster into space has not been the safest mode of travel ever invented. Elevators have a pretty good safety record. So, if it takes three days to reach orbit, it just takes three days. The amount of mass moved will be orders of magnitude cheaper than booster rockets. Plus, there will be more than one of these if it works well. Count on at least four. The first will be the hardest, but it will be used to build the rest.

 

[Machupo]

I take it no one has thought about biochemically powering lifters? You could design a large number of gear shaped lifters which could directly interact with the outer layer of the CNT...

Also, power transmission from the top to the entire strand, VLA's of solar collectors at the top or at a remote location, using MWCNT's as a single-mode fiber with a cladding layer (palladium doped before you roll the sheets, of course, kind of like a PB&J sandwich turned into a burrito) -- modern CNT's of "standard" size can withstand a couple keV signal, not only could you use the soft xrays for power transmission, but imagine the data transfer rates with that level of available multiplexing.

there are several technologies that would work fine to bring about something like this, but it's the sheer SIZE of the engineering project. It'd require an autonomous CNT production source with vast amounts of raw materials... like a carbonaceous chrondite asteroid or something or some other C-heavy body.... not to mention trying to power a molecular factory like that would be pretty ridiculous... so you'd have to snag an asteroid with a molecular construct that could develop its own factory (with little or no defects), re-route the raw material source into an energy rich environment (i.e. the sun)... also pretty ridiculous unless you could also have the "factory" mine propulsion fuel from the same raw material source (with pre-loaded energy, of course)... then you'd have to either have an intervention with the construct later on to guide it to earth (once the bridge was built), or you'd have to code a communication ability into it so you could remotely move it (again)....


at the outside realm of possibility (hah, like Ars' "5 to 10 years out" column), but it would require resources that are to this day unattainable.