Space Elevator within 15 years?

Great Debates
1

According to this article the only real technical issue standing in the way of a Space Elevator is the quantity of carbon nanotubes that are being produced. This number is moving into the tons/year and only getting greater, so this guys says we can make a Space elevator for about 6 billion dollars in the next 15 years!!!

This thread is to discuss whether the time-frame and financial predictions are accurate, the overall safety of an earth-based space elevator, as well as if it’s worth it right now.

I would say that any estimates from people involved in the Space program require tweaking. Just look at the Space Station. This would cost a ton I am guessing, however, the return would be tremendous. The article suggests within 6 years of operation you could have double your money back. Maybe 10? What I am concerned about is what happens if the thing falls? They intend to put it in the Pacific, but in KSR’s “Mars” trilogy, the elvevator falls and wraps around the planet a couple of times destroying everything in it’s way. Could this happen? Can it be avoided?

I would have to say that this would be one of the greatest things humans have ever created. It would change the world. Humanity would finally be able to start communities on the Moon (I can’t wait to go visit “Moonhattan”), Mars, and the asteroids - finally taking some eggs over to some other baskets. Science (certain branches anyhow: cosmology, astronomy, etc.) could jump by leaps and bounds with cheap access to space. Once multiple elevators were up, things would change pretty quick. From the water to land to air to space: our evolution continues. . .

DaLovin’ Dj

2

Geosynch orbit is only 22,500 miles above the surface of the earth, so if the station were to suddenly loose -all- rotational speed around the earth, it still wouldn’t wrap around the earth once, much less several times (Not knowing anything else about the author or books, that kind of makes me question the whole scenario). However, once it’s up there, if it were to start falling, it would follow the course of gravity and likely end up fairly close to the base.

It’d probably be much more likely for the whole thing to fly out into space, really. As long as the center of mass is put just slightly far enough out, it’ll run taunt against the cable (Which will effectively be “hanging” the station from earth). The only way something would bring the station down then would be rather disasterous anyway, I should think (Something like a meteorite strike or collision with another decent-sized orbiting object).

And it would probably have boosters for correcting its orbit in an emergency. It’d even have a fresh supply of easily replenished rocket fuel for it, too.

So yeah, it -could- happen that the station falls (Just like any other station), but between the ammount of supply this station would have and the inherent stability, it’d be rather unlikely, and usually correctible if it were. Stationing it out in the middle of the pacific would probably negate any damage from it falling beyond that of the station itself, though 22,500 miles of cable and a station might make for a bit bigger waves along the coastlines.

The time frame sounds a little optimistic, too. It’s an “assuming everything goes right” type of time frame. They might have the tech and materials then, but they also have to get political support, funding, etc. Still, if it were presented to a government when it’s almost ready to go, I’d be a little surprised if they -didn’t- jump at it. Imagine if the US could launch sattalites and manned missions with just a (22,500 mile) elevator ride. The savings in costs of rockets and the like would be immense, so it would eventually pay for itself. I don’t know how quick, though. Anybody know how much the US spends in launch materials each year?

3

I thought that the main problem with a space elevator was not the strength of the material, or the how of construction (not that these aren’t huge technical hurdles), but the conservation of momentum; as an object descends the rope, it is effectively entering a lower orbit but and is slowing down (it is traversing the circumference of the smaller orbit in the same time); this will result in terrific forces perpendicular to the rope.

(Somebody correct me there if needed; there’s a fairly thick layer of dust on my physics texts).

4

Just wanted to point out that the cable would extend well past the geosynchronous orbit. The article states that the cable would extend 62,000 miles (100,000 kilometers). Mangetout has a good point, but I’m guessing that by limiting the payload and the speed of the ascent / descent the forces may not be too great. I’m thinking that if this project were a slam-dunk, then Bill Gates would have signed on as an investor already.

5

15 years to build a structure 22,500 MILES!!? Um…yeah…whatever. Probably more like 150 years.

Let me dust off the old Civil Engineering degree:

CONSTRUCTION:
The tallest structures to date built by man are on the order of about 1000 feet tall. This does not include conceptual ideas like the 200 story Mellenium tower I saw on the Discovery Channel or Frank Lloyd Wrights Mile High Scyscraper. Assuming that there are materials that could handle the stresses (which there aren’t at this time), we don’t have the construction techniques to build something that big.

I imagine you would have to start on the ground and in orbit (Lagrange point?) and feed the cables towards each other. The cable in orbit kept there by a counterweight. Kind of how they build suspension bridges. So how would you like to be “hanging steel” er “hanging” carbon fibers" 100 miles up? As cool as it might sound, there are logistic problems with getting workers and their supplies (which have to include space suits and such) onto a cable that stretches 1000s of miles in the sky.

COST:
How many shuttle trips will be required to put material in orbit to build a space elevator? And those shuttles aren’t delivering hollow, titanium modules. They have to deliver really heavy structural elements. Not to mention the shear volume of materials will cost a fortune.

BENEFIT:
With all those shuttle trips, you could have placed enough sattelites in orbit to walk from the earth to the moon. Unless you are loading massive Star Destroyer size ships in orbit, you don’t really need a space elevator.

SAFETY:
Nothing like this has ever been built before. Imagine if it starts to oscillate like the Tacoma Narrows Bridge or starts dropping shit like the Hancock Tower in Boston. And we’ve been building bridges and buildings for centuries. And at 25000 miles high, that shit is breaking up and coming down EVERYWHERE if something goes wrong. Probably for years since much of it will stay in orbit.

6

** msmith537**, it looks like you didn’t read page two which addresses many of the engineering / construction issues that you raised. I’m not saying that it is feasible, but at least they have a plan that doesn’t require a large number of shuttle trips. As a matter of fact, the article only mentions two shuttle flights being necessary.

7

mrsmith, methinks thou didst not read the link in which all of your issues are addressed.

The plan uses two shuttle flights. That’s it.

They lower a very thin cable to the base station, and “climber” machines go up the cable weaving more material onto it, making it thicker and stronger.

8

Don’t you have to clear everything out of low earth orbit first? Otherwise the tether’s going to get broadsided by something moving at orbital speed sooner or later.

9

msmith, read the article. The concept of building the space elevator is not that you build it up, but that you drop the starting cable down. For this, again according to the article, you would only need two shuttle trips. You then strengthen the starting cable with robots inching up the starting cable, laying additional layers.

Sua

10

I used to work in a laboratory that produced carbon nanotubes. I’m not really supposed to talk specifics, but we were still trying to get tubes of visible length – I’m talking millimeters here. We were getting better, but as of the time I stopped working there four years ago we still couldn’t make a rope or a fiber or anything. Still, people were lining up to buy whatever we could produce, microscopic or no. Four years is a long time, but unless there have been some major advances that I haven’t heard about, no one’s going to be weaving a 20 foot rope, much less a 23000 mile cable. Have there been major advances? I’ll admit to being out of the loop on nanotube research. Just producing ton-loads of tubes isn’t going to immediately solve the problem; it’s like having a ton of graphite unless you can cause them to join or knit somehow. We could never get 'em to link up, you see.

11

From the Article

**The first cable could launch multi-ton payloads every 3 days. **

Assuming a round trip for the elevator, thats 22,000 miles in 36 hours.

611 miles/hour. :eek:

hmmmm

12

I’m not too good at math, but last time I checked there were 24 hours in a day. Even so, 300+ mph is still pretty fast to climb a cable.

13

Well, roundtrip would be 44,000 miles, so the original 611 mph would be correct.

14

Enipla assumed a round-trip in 3 days so . . . 1-1/2 days up; 1-1/2 days back.

Still, most of that travel would be in airless space so a 600+ miles per hour speed doesn’t sound unreasonable, even taking into account the need for lengthy, slow deceleration near the geosync end. :slight_smile:

The solution to the problem of presently existing nuclear waste could seem to make any worries about cost nearly trivial: The savings alone would easily pay for the entire elevator’s cost; this saying nothing about the ability to safely get rid of radioactive waste which is even now leaking into the U.S. groundwaters.

15

Thanks munch.

This

**Once secure, a platform-based free-electron laser system is used to beam energy to photocell-laden “climbers”. **

And this

"If budget estimates are correct, we could do it for under $10 billion. The first cable could launch multi-ton payloads every 3 days. Cargo hoisted by laser-powered climbers…

From the story.

Doesn’t add up to me. You use laser powered climbers that are being pushed up from a platform based laser system. If the climbers are not physicaly climbing the cable why do you need super strong cable. Why do you need a cable at all?

16

D’oh!

Well, at least I said that I wasn’t good at math. I think it’s time to go to the pub to lubricate my brain cells.

enipla, the way I read the article was that the lasers would be used to energize the photocells which would then provide electricity for the climber. I don’t think they are proposing direct levitation using the lasers. Presumably, electric motors (or something) would have to grip the cable in order for the “elevator” to climb.

17

I think you are misunderstanding that. The climbers are physically climbing the cable and are not being “pushed up” by the laser. Think of them as “solar powered” but instead of getting the photovoltaic energy from the sun to power the onboard electric motors - they get it from a ground based laser beam. This allows them to be lighter than if they had to carry their own fuel source.

I must admit I am skeptical about this scheme. Is it really worth it? How much energy would be saved? I can’t run the numbers but I suspect that after factoring in the weight of the elevation device (the vehicle - not the cable), the conversion efficiency of the photovoltaic cells that will power the vehicle, the efficiency of the laser, and the energy loss from the friction of the cable itself, the proposed scheme might be less efficient than conventional rockets. And what’s the point of building it then?

If we had photovoltaic cells and lasers that operate at reasonable efficiency, the scheme might make sense. But we don’t, and the development of those things semms pretty far off.

18

From this Space.com story (link), enipla, rsa, the lift-power seems to be magnetic. There is a picture.

19

Opps,

Photocell laden climbers.

That makes better sence.

Aren’t we still going to have problems with the conservation of momentum? If its going between 300-600 miles/hour, that doesn’t give the cable much time to change the horizontal movement of the payload.

Still that may be the least of the problems. If you change the time to 30 days per launch that would work out to 240,000 tons per year.

20

What part about swinging nuclear waste off the earth like a giant teatherball seems “safe” to you?