Space Elevator Could Cost Less Than You Thought

WolfWithoutAClause writes: "We've had Space Elevator stories before on Slashdot, mainly saying how impractical they are for the foreseeable future. Now however, there's an 8M pdf paper on NASA Institute of Advanced Concepts [NIAC] website that says it may now be possible with existing materials and can be done for about $40 billion. That's less than the entire launch market for a single year. If he's right, the first elevator may be complete in 10 years time, with the second and third following 2-3 years afterwards."

Comments

It's a tether

[Dr. Tom]

This version of the Space Elevator doesn't go all the way to the ground. That's why it can be built with existing materials. You still need a (hydrogen fueled) rocket to get to the dock at the lower end of the tether, which is about 250 km up. However the dock is moving significantly slower than orbital velocity, which increases payload and allows cheaper (more reliable & maintainable) rockets.

Re:It's a tether

[bofh31337]

A full 35,000km long space elevator would not be practical. Something of that great length would span many g-forces and you would need a large counter-weight above geo stationary to have zero velocity at ground level. Having that kind of taper from bottom to top would require a huge mass The big difference with a 250km tether is the center of attracting (and mass for that matter :)) can be in many more places. I'm thinking the best idea isn't so much a space elevator but a space slingshot using a pair or more of gravity stabilized fully rotating cables. It's an interesting idea that's been thrown around for many years.

Re:It's a tether

[WolfWithoutAClause]

> A full 35,000km long space elevator would not be practical.

That's what I thought, but read the paper. He claims it's possible; and describes how, how much and how long. The carbon nanotubes are strong enough now; or atleast that's the claim.

Yes, it does go all the way to the ground

[iktos]

It's about a 96000 km, fixed at the bottom end, with a counterweight at the far end.

It's 50 mm wide and with a cross section of 2 mm^2 (which makes it good for lifting 20 tons, payload 12, every 97 hours). But upgradeable, of course. Cable mass 572 tons, counterweight 621.

Many parts of the building are pretty well thought out, like first sending down a thin cable and build the rest by having climbers adding more, and then using the used climbers as the counterweight. (Also, the climbers increase in mass as the cable grows stronger, from a total of 619 kg to 20 tons. Beam powered from the ground.)

The initial cable would mass 19.8 tons, with fuel the deployer would mass 190 tons, but that's still a reasonable number of Shuttle missions.

the paper, not the slides

[blamanj]

That 8M download only gives you the slides - pretty pictures but no text. The actual phase I paper is here. It's a 15M download - and you can year the server creaking under the strain.

Angular momentum

[p3d0]

When something's going up the elevator, where does it get all the angular momentum it needs to stay in orbit? Does the climber have rockets? I don't see them on the diagram.

Re:Angular momentum

[PhuCknuT]

I don't agree however that you could cancel the effect out by timing the subsequent launches. The issue of total angular momentum needs to be addressed. Subsequent launches could only cancel the angular momentum if they were somehow launched from the end of the cable with opposite angular momentum.

I think you misunderstood what I meant. The cable would lean west (very slightly) during a launch, and once the payload finished its ascent, the cable would swing back towards vertical. If left alone at this point, it would continually swing back and forth. It's not the transfer of angular momentum away from earth that I was talking about cancelling, it's the swinging of the cable. If you time your launches so that they occur while the cable is swinging back east, the eastward momentum would be canceled out by the westward momentum that the cable gains from the cargo.

As for why it would swing like a pendulum, I'll try to explain the best I can without drawing pictures. :) As long as the cable is leaning westward, the cable will be gaining eastward angular momentum from the earth. This is simply because the cable is under tension and no longer perpendicular to the orbit. Likewise, when it leans east, the cable tension will have a westward component pulling on the counterweight. As the cable swings back and forth, the angular momentum of the whole system (earth, cable, counterweight) will remain the same, but a small amount of the momentum will slowly transfer back and forth between earth and counterweight.