Elevator Into Space

Space.com ^

[nuke rocketeer]

Bradley C. Edwards, president and founder of Carbon Designs Inc., is the driving force behind the space elevator, a purportedly safer and cheaper form of transporting explorers and payloads into space.

Although the idea has appeared in both technical and fictional literature for decades, the drive to bring it to reality belongs to Edwards. A cable extending from the Earth’s surface to outer space is kept under tension by the competing forces of gravity on Earth and the outward rotational acceleration of the planet in space. Once the cable is aloft, the elevator will be ascended by mechanical means.

[nuke rocketeer]

He seems hopeful it will happen soon. We'll see. Right now in my old age, it seems like all the talk of fusion power being 'right around the corner'.

[Egon]

Disembodied voice: "2nd floor: lingerie, make-up, rebreathers, jewelry, micro-meteors, and Tang. Watch that first step, please!"

[lafroste]

I had read that the space elevator wouldn't work beacause the tensional stress required in the cable was unendurable by any known material. Has that changed in the recent past?

[Red Badger]

This is the modern version of the Hindu Rope Trick!........

[edwin hubble]

Kevlar was introduced about the time Arthur Clarke wrote "Fountains of Paradise", with a popular science fiction plan for the elevator. It was about an order of magnitude away from the strength/weight necessary.

Today nanotube technology is approaching the point of necessary properties, but it will be decades before the massive production scale and uniform quality make the elevator possible.

The project is ten times the size of Apollo or Manhattan or the space station, so the biggest questions will be about economics and strength of leadership.

[Reaganesque]

"The biggest challenge to the space elevator has been developing a cable tough enough to extend 62,000 miles without breaking. This, Edwards explained will be solved with carbon nanotube composites - tiny bundles of carbon weaved together to form a ribbon that will be stronger than steel. His startup company, Carbon Designs, Inc., is currently focused on developing this technology."

So, they don't have a material that's strong enough, yet. But given the rate of progress in the nanotech field and the number of people working on it, it's only a matter of time.

[marktwain]

So, they don't have a material that's strong enough, yet. But given the rate of progress in the nanotech field and the number of people working on it, it's only a matter of time.

Essentially correct. Though it seems unlikely that an Islamic society would find much use for such a project. As private space exploitation grows, the profitability of such a project will become obvious.

[Military family member]

According to the article, the elevator would travel at speeds as slow as 10 MPH. The international space station is 220 miles above the earth? Who's going to sit on an elevator for 22 hours?

Look, if we can perceive of technology capable of 200-300 mile high elevator, then why not look to develop technology similar to that from Star Trek--the transporter, or the shuttles--which could get a person from the ground to space in mere minutes? After all, if we're going to fantasize about future modes of transportation, then let's really use our imagination.

It seems to me that even if this guy is serious, he's also looking in the wrong direction for scientific advancement.

[nuke rocketeer]

Actually, of all the proposed non-rocket methods of getting to LEO, this one is just behind the laser launcher as far as practicability. The proper material for a space cable may remain out of reach, but a laser powerful enough to launch pods into orbit will be available soon. A space elevator would provide the cheapest way for mass transportation. All you would need is electricity, and a good chunk of it would be provided by the elevators going back down to earth. I agree that 10 MPH is unrealistically slow, but 100-200 mph is not.

[robertpaulsen]

Lateral speed at the surface of the Earth: 1000mph
Lateral speed at 62,000 miles: 17,300mph

How do we go up and increase lateral speed without bending the cable into a big "C" shape?

Lateral speed is everything. Taking an object up the elevator and pushing it out the door at 100 miles in altitude (shuttle orbiting height) will do no good. It doesn't have orbital speed to stay there. At any elevator height.

[The_Victor]

Lateral speed at the surface of the Earth: 1000mph Lateral speed at 62,000 miles: 17,300mph

How do we go up and increase lateral speed without bending the cable into a big "C" shape?

A little basic physics. A point on the outside of a tire moves faster that a point toward the rim. The speed increases linearly with the radius distance from the point of rotation.

w=vr Angular (rotational velocity) is velocity time radius

You put the termination point at geostationary orbit where the speed needed to maintain orbit is equal to the rotation of the earth.

[Smokin' Joe]

How do we go up and increase lateral speed without bending the cable into a big "C" shape?

Just one problem. Really. How do you anchor the darned thing?

[RandallFlagg]

They could do it if they had an interociter.

[ctdonath2]

Orbital physics is really whacky. From what I've gathered, once you get it set up right, it doesn't actually need to be attached: the whole elevator cable is orbiting the Earth, with the lower end just sorta dangling there.

[RandallFlagg]

How do you anchor the darned thing?

I hear Rosie's available. AND an added bonus: She's good with machinery...
/rimshot

[Gorjus]

How do we go up and increase lateral speed without bending the cable into a big "C" shape?

That's the biggest issue.

The concept behind the space elevator is that the string is acually moving in synch with the earth's rotation, which means you have orbital velocity at geostationary altitude (22,300 miles). Most of the designs I've seen go up to about 36,000 miles, at which point the terminus is at earth escape velocity (in order to keep up with rotation). Letting go of something at that point would fling it off into interplanetary space. As you pointed out, though, at 100-200 miles altitude, the string is moving at much less than orbital velocity and anything released there would fall back to earth quite quickly.

However, anything rising up the cable would need to be accelerated to keep up with the string - and that would slow the string, eventually leading to collapse. Something would need to be done to replace that angular momentum - every time the 'elevator' went up. That would take as much momentum transfer (fuel) as it would take to orbit the same amount of mass using conventional means, unless you could recover and de-orbit as much as you're lifting into orbit. Right now, there's no concept on how to do this.

It's also not trivial to produce the required strength. Actually, carbon nano-tubes are about an order of magnitude less than the required strength-to-weight, and they're nano-tubes. Just a bit short for the job. Carbon-carbon bonds, as used in the nano-tubes, as also the strongest bonds known within current chemistry/physics. Getting that extra order of magnitude is not a job for engineers, it's a job for basic science - a breakthrough in theory, not just a refinement of technology.

Nonetheless, I believe both problems can be solved. I'm not sure the economics will ever work out, though. Like a lot of problems, it's more social than technical.

[Smokin' Joe]

Yeah, but if I had to climb over her to get on the elevator every time, I'd take the stairs.

[robertpaulsen]

"The speed increases linearly with the radius distance from the point of rotation."

I agree. Obviously, it must.

My question is, what causes the speed to increase? Yes, as the elevator rises, angular speed increases, but the elevator is "rubbing" against one side of the cable on the way up.

Let me put it this way. Think of a space launch. We don't fire the rockets straight up. They'd just fall right back down.

At a certain altitude, the rocket pitches to pick up that angular speed.

[ctdonath2]

Who's going to sit on an elevator for 22 hours?

Me! I sat on a plane for 20+ hours to get to Korea; I'm willing to sit on an elevator for 20+ hours to get into space.

Look, if we can perceive of technology capable of 200-300 mile high elevator, then why not look to develop technology similar to that from Star Trek--the transporter, or the shuttles--which could get a person from the ground to space in mere minutes?

Because transporters are still remote freaks of way-out-there quantum mechanics, and shuttles are what we're trying to move away from (remember Challenger & Columbia?).

The space elevator is NOT way-out-there sci-fi fantasy, it is a realistic idea. It's just basic well-understood physics (ok, orbital mechanics is kinda strange, but still just an extention of mechanical physics). The only thing really inhibiting construction is lack of strong enough materials, which recently-developed carbon nanotubes seem to be; it can be done, we just need to work out large-scale production.

There's a difference between imaginative stories and "we're working on that."

[ctdonath2]

they're nano-tubes. Just a bit short for the job.

They're also getting longer. Was just a few years ago that "buckyballs" were first created/discovered, and didn't take very long before they were extended into "nanotubes" a few millimeters long. Just a matter of time before they're cranked out by the mile.