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

9/11

[Anonymous Coward]

Not to bring up any bad memories, but if history has taught us anything - this will be a target. How could you keep something this long and lanky safe from planes?

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.

Re:It's a tether

[JohnPM]

Not sure you were reading the same document as I was. The cable certainly does go all the way to the ground. Also, the cable described cannot really be built with existing materials because it relies on carbon nanotubes. While this material does exist, I don't believe it has ever been used as a construction material outside the laboratory.