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

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.

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.

Re:Yes, it does go all the way to the ground

[Anonymous Coward]

One of the interesting things about this design is that the counter weight must be in a strange state of having superorbital speed.

Take the differential element of the wire that sits at the geostationary orbit. That element sits in geostationary orbit, and would be weightless.

The thing is, all points on the wire would have to have exactly the same orbit time, if the wire is to stay straight.

The counter-weight would ALSO have to have an orbit time of exactly one day. This means that it would be moving faster that objects would naturally at that orbital radius. How would that be done? By having the wire support tension, just like flinging the counterweight around on the end of a string under tension.

The base of the wire would have to be attached to the earth in a very strong manner to support that tension.

A nice pair of scissors would send the counter-weight into a very large orbit indeed. :-)

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.

Re:9/11

[xah]

Who marked this post as flamebait? It makes a legitimate point.

Among others, this "space tether" would be vulnerable to the following terrorist attacks: missle, bullet, bomb, acid, human piloted aircraft, remote controlled aircraft, ground vehicle, laser, and fire.

These are just a few of the feasible methods to cut such a cable. If a terrorist wanted to place an infiltrator inside the space elevator, more attack options would be available to them.

This space elevator idea doesn't sound feasible when the security problems it would engender are considered.

It's a bit more robust than you think...

[Anonymous Coward]

First of all, if you break the cable down low, the bulk of it just "springs back" into an elliptical orbit with the same perigee.

Secondly, a lot of plans call for the cable to join a 15 km high tower, since building up from the earth is feasible for that altitude, and chopping mass off the bottom end of the cable translates directly to increased cargo capacity. 50,000 ft is higher than most planes fly.

The scary scenario is the cable breaking up high, e.g. the counterweight coming loose. The cable would fall to earth, wrapping around the equator multiple times as it does so, cracking like a whip. All of the energy spent launching it would come down in a long thin bang.

Re:disaster

[Anonymous Coward]

This scenario has been beautifully described in Robinson's "Red Mars". Get a copy and read it - it's fascinating.