Space Elevator May Become Reality

mojotek writes: "The NASA Institute for Advanced Concepts has a study(15Mb pdf) about the feasibility of a "Space Elevator" comprised of a 22,000 mile long cable built out of carbon nanotubes. In theory, it would be able to carry loads of 20 tons to space without using a single rocket engine. Sounded way too sci-fi for my taste at first, but this article at TechTV actually helped fill in the holes."

Comments

Last time this came up on /.

[Bill Currie]

I did the math and worked out that if you gibbed the cable (say 1m chunks), you'ld wind up with something like 25-30 thousand km (I don't remember the exact figure) of the cable crashing down on earth and the rest flying off into space. However, I didn't figure out if the cable would fall east or west (west would be better, but I think it's less likely). Either way, that's a little over 1/2 way around the world and while the only land mass likely to be hit is Africa, I don't imagine the impact with the water would be particularly fun (possible tsunami).

Yes. Re:Rotational energy

[HiredMan]

The short answer is: Yes.
Physics works everywhere all the time. When you climb a flight of stairs or walk up a hill it slows the Earth's rotation - and it speeds back up as you walk back down.

No - seriously - just as an ice skater's rotation slows or speeds as they extend or contract their arms the same principles apply to all rotating bodies. Everytime we slingshot a space vehicle around the Earth we are effectively transfering some of the planet's energy to the vehicle and that energy has to come from somewhere.

But the amounts here are so small that the effect is not measurable or "effective" in the scale of anything we could notice. It's like the fact that anything with mass has a gravatational field - but you don't notice the effect of the gravity created by your pen.

=tkk

Pie closer to hand

[Yurian]

Ok - The space elevator is a lovely concept, but it's only just possible with the theoretical limits of where we can go with materials technology - so its going to be pie in the sky (or lack there-of) for a long time yet.

There are some variations on the idea though,like this one, that are close to being possible with today's technology, and can even be provisionally costed. Basically the idea is to construct an elevated runway about 100km up, and use mass drivers to hurl stuff into orbit. At that altitude the saving from air resistance is huge and mass drivers become very efficient

At this stage, NASA speanding serious time thinking about space elevators is probably no more useful than daydreaming. Thinking about this kind of thing is probably more productiove though, becuase something might come of it in the medium term, and its almost as efficient as an evelator anyway - with the decided advantage of not being able to collapse and strangle the planet.

(Since I heard about this from a NASA researcher, maybe Im being a little harsh to accuse them of daydreaming)

This Won't work - They forgot the taper factor

[szyzyg]

One big issue they missed is the fact that a carbon nanotube cable still isn't strong enough to support it's own weight without tapering the cable correctly, at the middle it has to be about 10 times thicker because the stresser are highest at geostationary orbit.

The deployment method they're using doesn't take account of the fact that you need the thickest part to always be at the middle - if you simply unroll it the way they suggest then the incorrect thickness profile will result in the cable exceeding it's breaking point and snapping.

What they need to do is unfurl a cable like this from geostationary orbit simultaneously up and down at the same time. The Mechanism to do this would have to be very delicate at unfurling the last kink or the cable will again snap.

The cool thing about this is if you figure out what kind of weight you want the cable to support then you can come up with an idea of the amount of energy stored in the tension. If the cable snapped at any point then the amount of energy released would be pretty phenomenal. From each end of the snap you'd generate a compression wave which would get stronger as it travelled along the cable, after a while of picking up energy it may turn into a shockwave and snap the cable again (essentially shattering the cable). If it doesn't then the wave will have energy equivalent to nuclear weapons when it reaches the endpoints and the waves transmit themselves into the supporting structure....

Re:Just a pie-in-the-sky idea

[mmontour]

And it is exactly that, sci-fi. Sure, carbon nanotubes are incredibly strong. And they're also on the order of a few microns long. Now, this cable needs to be a few hundreds of thousands of meters long. You do the math.

The semiconductor industry figured out how to make large single crystals of ultra-pure silicon, then pattern the surface down to a ridiculously fine resolution. The fiberoptic folks figured out how to make glass so clear that a light pulse can go through many many miles of it and still be recognizable at the other end. Molecular biologists can "amplify" single molecules of DNA into macroscopic quantities.

I wouldn't be so quick to say that we will never be able to make carbon nanotubes that are long enough to be useful as structural materials.