Space Elevators

[imported_Hamzter]

For those of you that don't know, a space elevator is a way of getting into orbit by climbing a huge, ultra stong cable that's teathered to earth, the other end floating in space, the spin of the earth would mean that the cable would straighten and support itself. I've read a few estimates of the cable length needed, normally between 20,000 and 40,000km long, made of carbon nanotubes, unfortunately they've only been able to make this material in the lab a few mm long so far.

Anyhow, I've been wondering about how they'd achieve something like this, assuming the materials can be created in long enough lengths quick enough, what problems would there be and how would they solve them?

The biggest problem seems to be if that cable breaks, a few hundred tons of cable falling to earth can cause alot of damage. I read a report a while ago suggesting that since it was a 99% chance that the cable would break below 100km (only things that can really break it above that are collisions with satellites and meteors), several cables could be used which merge at about 100km, but then you have the problem of and climbing vehicles would have difficulty getting past (probably a minor problem).

Other problems were things like how would you power the climbers? You need alot of energy to climb 20,000km of cable, would anyone risk using nuclear power or would you transmit the power somehow to the vehicle?

I'd be really interested to hear anyones thoughts on the idea, and how we'd get past any of the problems!

 

[jagec]

Powering the climbers would certainly be easier than using rockets...it would take less energy, AND you can run power lines from ground power supply stations for most of the climb.

 

[bobsmith1492]

hm... so if a cable is long enough the earth's rotation would fling it out vertically? Last time I tried standing a cable straight up it fell down.

 

[TheStu]

yeah I would wonder if it was really feasible to attache a 40 000 km cable to a shuttle and launch it... I mean what if a cessna flies into it at night.. or a migratory bird? or really anything.... i suppose... I don't claim to have any solid knowledge in the area I'm just trying to think it through reasonably r something.

 

[mrSHEiK124]

wow, just think, several tons of cable, hitting the planet. lol, it'll probably knock it out of orbit or something, maybe next century

 

[imported_Hamzter]

I've thought about about running power cables up it, but there's 2 problems with that, first of all electric cable weighs alot, it could easily be heavier than the actual elevator cable. Second, when you've got a several thousand km long electric cable, the resistance becomes fairly high (or rather, extremely high, you'd need to pump some serious power into the cable at the bottom to get anything half decent out of the top).

Lol bobsmith, doubt you've got the kind of length cable needed, the top end of the cable needs to be in a very high orbit to provide enough force to support itself. The idea is theoretically sound, it's an engineering problem rather than a scientific one.

As for launching the thing, I don't think you'd actally tie one end to the ground, and the other to the space shuttle, that would be a bit silly, you'd have to launch some of the cable into orbit first, then feed it down to the ground from there. It'd then be tethered to the ground, and more layers of the cable are added by climbers that climb up (or down if the tether's not strong enough to support it at first, they'd have to be launched into orbit and then attach to the end of it somehow though) the tether. I doubt birds would cause much of a problem, these things should be stronger than steel.

A more serious problem though is lightning, serious damage could be done to the cable if it was hit. I suppose you could add a lightning conductor a few miles long up the side of it, don't know how well that would work though. One of the crazier ideas I've had, is to use lasers, I've been told (may be complete nonsense) that high power lasers can be used to create a lower resistance in the air (ionisation of the air or something), so the lightning would be more likely to travel along the beam of air rather than down the cable. It's a pretty crazy idea though, I'd actually be suprised if it were possible.

 

[JonB]

The articles I've read about this before always indicated a connection point at the equator. The carbon nano-tube would be manufactured in space and lowered to earth meter by meter, captured and then connected. When I first heard this idea in old science fiction books, they hadn't invented the nano-tube structure yet but hypothesized a similar mono-molecular thread along the lines of the thread in Larry Niven's Ringworld.

As far as lightning, there are places on Earth where lightning is very rare. Any of you folks spent time at the equator? How are the storms? Plus, stormy weather is a very low altitude phenomenon compared to the length we are concerned with.

 

[imported_Hamzter]

Hmm, I'd have thought manufacturing the stuff would be pretty complex, current methods employ lasers and high temperatures, something capable of producing it would probably weigh hundreds, if not thousands of tons, would it not just be easier to make it on earth and then launch it into space?

 

[bobsmith1492]

Why not just combine the support cable with the electric cable? One huge metal cable for support and electricity - well, two cables for the entire circuit. I'm sure 2 1-foot-diameter gold cables could carry enough current......

 

[JonB]

From Wikipedia:

In theory, metallic nanotubes can have an electrical current density more than 1,000 times stronger than metals such as silver and copper

http://en.wikipedia.org/wiki/Carbon_nanotube

Perhaps the column could carry it's own electric charge. Wikipedia says that the Chemical Vapor Deposition method shows promise for making large quantities cheaply, but you have to "feed the process." That could be tough in space to get enough raw material, plus it probably is a "once you start, you don't stop" process.

http://space.com/businesstechn...e_elevator_021120.html

 

[deveraux]

Personally, I think supplying all that power from earth isn't really the best option. I mean, you're out in space, solar power is abundant. Better still, if they could come up with some way of harnessing various types of power along the entire length of the structure, although I am not sure how feasible this idea is.

 

[imported_Hamzter]

If they manage to create the cable so that the resistance is low enough, it'd be a great way of powering the climbers, but I doubt they could do that reliably. Solar power also aint really an option as you need alot of panels to drive the climbers, they'll probably be carrying a good few tons.

Its been suggested that some kind of laser can be used to transmit power to the climbers, this would probably have to be done from an orbiting solar power station though, as the beam would be absorbed by the atmosphere from ground level (the climbers could carry some fuel to get past the first 100km or so through the atmosphere, then switch to the laser power).

While looking round the internet, I came across a post on a forum suggesting that since the cable is passing through the earths magnetic field, you'd get a huge voltage difference along the length of the cable, surely that wouldn't happen? Is the cable even cutting the field in a way to cause this? (I suck at magnetic field lol)

 

[mwmorph]

Originally posted by: JonB
From Wikipedia:

In theory, metallic nanotubes can have an electrical current density more than 1,000 times stronger than metals such as silver and copper

http://en.wikipedia.org/wiki/Carbon_nanotube

Perhaps the column could carry it's own electric charge. Wikipedia says that the Chemical Vapor Deposition method shows promise for making large quantities cheaply, but you have to "feed the process." That could be tough in space to get enough raw material, plus it probably is a "once you start, you don't stop" process.

http://space.com/businesstechn...e_elevator_021120.html

1. ufortunately, carbon is the strongest nanotube material or so iv'e heard so metal nanotubes wont be practiacl. we're looking for a weight advantage here.

2. why not nuclear power?the cassini and gallaleo both used it to power electricity hungry instrumnts for years. it is easily possible
or how bout fusion?(scientists, a team of us and euro union plan to d othis by 2010 and have $6 BILLION in finiancial backing by the goverments)

 

[imported_Hamzter]

Nuclear is a possibility, there might be alot of people against it though, everyone's frightened to death of nuclear devices.

But fusion? Doubt it somehow, the ones in development at the moment are nowhere near operational, I doubt anyone will even reach ignition for another decade at least, let alone make a safe, reliable, compact one. It'd probably be a bit overkill aswell, a fusion reactor could probably put out megawatts of power.

 

[JonB]

mwmorph, the metallic nanotubes are still carbon, they just have the properties of a metal (conductivity) instead of the other common nanotube forms, insulators and semi-conductors. Right now, they can't reliably manufacture only one type. I'm certain that enough research will eventually clear it up. The Wikipedia article is pretty lengthy and covers all that.

The Space.com article describes how the first shuttle flight would take up a very fine nanotube filament cannister, put it in geo-sync orbit and lower it to the sea-based platform. Then strand after strand would be added to the original strand, increasing its strength, just like multi-strand thread is stronger than a single filament. Over several months to years, the final column would be able to support high mass items in electrically powered elevator cars. They would get their power from earth based laser pulses hitting their photo-voltaic panels. Estimate three days to climb, so it isn't moving fast at all (slower than a person walking).

 

[DrPizza]

There was a large article dedicated to this in Discover magazine about a year ago... we're just about to the level of having the technology to begin such a project...

They also pointed out that whoever builds the first one, wins. Because after there's one, it would be a piece of cake to use that one to build others.

 

[imported_Hamzter]

Lol, doubt it'd travelling slower than a person walking, how many people can walk 40,000km in 3 days???

 

[otispunkmeyer]

Originally posted by: bobsmith1492
hm... so if a cable is long enough the earth's rotation would fling it out vertically? Last time I tried standing a cable straight up it fell down.

thats the idea

they will have to use those carbon nanotubes to build such a thing, a steel cable would just collapse under its own weight

what i have trouble thinking about is that materials have different properties at different temperatures and possibly react in different ways to certain sorts of radiation and pressures

the lift will be at atmospheric pressure on the ground at a nice temp with normal weather conditions, then its off in to space where the temp drops wat ? 3 or 4 kelvin? that would sure make alot of materials very brittle like ceramics. then you got all the suns radiation attacking it. are there materials that can exist in totally diferent environments at the same time?

or would they have to make it into sections, with each section having a different set of properties to suit the environment?

 

[JonB]

You don't have to travel the whole length. Just up into space, then launch the payload, then head back down for another payload.

 

[Calin]

In the "Mars" (Red Mars, Green Mars, Blue Mars) trilogy of Kim Stanley Robinson there is such a space elevator. For Earth, the mass of the cable below 36 000 km (geostationary orbit) should be "supported" by a "countermass" above 36 000 km. I would say that without such a countermass, the cable would need to be some 70000 km long, or one fifth of the distance to moon.
A beautiful description of the Space Elevator was made by Arthur C Clarke in one of its books.
Such a "space elevator" would be capable to "sling" spaceships using the velocity of its terminal (space) end.
They used chemical batteries, batteries who were used by climbing "crafts" and loaded by descending crafts. There were some stations on the way, stations were the batteries were changed.
Energy wise, the electric climbing system would have an efficiency at least an order of magnitude higher than the rockets we use now (but still, the current battery technology would be unable to climb a craft even a significant portion of the way). In Clarke's book, the crafts were accelerating to several hundreds of km/s before entering on the "elevator".
Also, being on the top of a mountain helps alot by reducing the distance travelled in the atmosphere

 

[DrPizza]

Originally posted by: otispunkmeyer

Originally posted by: bobsmith1492
hm... so if a cable is long enough the earth's rotation would fling it out vertically? Last time I tried standing a cable straight up it fell down.

thats the idea

they will have to use those carbon nanotubes to build such a thing, a steel cable would just collapse under its own weight

what i have trouble thinking about is that materials have different properties at different temperatures and possibly react in different ways to certain sorts of radiation and pressures

the lift will be at atmospheric pressure on the ground at a nice temp with normal weather conditions, then its off in to space where the temp drops wat ? 3 or 4 kelvin? that would sure make alot of materials very brittle like ceramics. then you got all the suns radiation attacking it. are there materials that can exist in totally diferent environments at the same time?

or would they have to make it into sections, with each section having a different set of properties to suit the environment?

well, not quite the idea...
The cable doesn't simply stand up like a tall structure. Think of it this way: go outside, grab a rope, and start spinning around. Notice that now that you're spinning, the rope extends outward from your body. The earth spins...

 

[Armitage]

Originally posted by: Calin
In the "Mars" (Red Mars, Green Mars, Blue Mars) trilogy of Kim Stanley Robinson there is such a space elevator. For Earth, the mass of the cable below 36 000 km (geostationary orbit) should be "supported" by a "countermass" above 36 000 km. I would say that without such a countermass, the cable would need to be some 70000 km long, or one fifth of the distance to moon.
A beautiful description of the Space Elevator was made by Arthur C Clarke in one of its books.

Fountains of Paradise

Such a "space elevator" would be capable to "sling" spaceships using the velocity of its terminal (space)

Note that only @ geo would an object on the elevator have circular orbit velocity for that altitude. Circular orbit velocity @ geo (43000 Km) is roughly 3 km/s. That means at low earth orbit - say 7400 Km the elevator is only moving roughly 0.5 Km/s while circular orbit velocity there is on the order of 7 Km/s. There's alot to be said for getting above the atmosphere, but you still need to come up with alot of dV to make orbit - plus plane change on top of that. Unless your going to GEO of course.

end. They used chemical batteries, batteries who were used by climbing "crafts" and loaded by descending crafts. There were some stations on the way, stations were the batteries were changed.
Energy wise, the electric climbing system would have an efficiency at least an order of magnitude higher than the rockets we use now (but still, the current battery technology would be unable to climb a craft even a significant portion of the way). In Clarke's book, the crafts were accelerating to several hundreds of km/s before entering on the "elevator".
Also, being on the top of a mountain helps alot by reducing the distance travelled in the atmosphere

I haven't read any of the papers on the ideas, but I wonder how they expect to handle the issue of collision with orbiting objects - that's a tremendous amount of energy, and everything has to cross the equator, so it's a prime target. I think Clarke has commented on that actually - saying that we have to build the elevator while the orbital population & debris environment is still potentially manegable, or we'll miss our window of opportunity.

 

[Calin]

Yes, lauching space ships was to be made by climbing their parts up to the "countermass" (that would be above geosynchronous orbit), and so having a speed bigger than the orbital velocity for that altitude, assembling it there, and then simply allowing it to depart.
The countermass must be above the geosynchronous altitude (like 36 000km from the earth surface, IIRC) to compensate for the entire cable length (and mass) that is below that altitude, and attracted to Earth.
The idea for Mars' space elevator was to create a swinging motion to avoid its moons. However, this could be applied only for several big moons/asteroids, and not for some hundreds/thousands projectiles

 

[Armitage]

Originally posted by: Calin
Yes, lauching space ships was to be made by climbing their parts up to the "countermass" (that would be above geosynchronous orbit), and so having a speed bigger than the orbital velocity for that altitude, assembling it there, and then simply allowing it to depart.

Which is great for spacecraft departing earth orbit. But supersync satellites are of limited utility for earth orbit. I wonder what the trade space looks like for LEO? What's the best altitude to drop a satellite whose final destination is say - 8000 Km semi major axis?

Don't get me wrong - a space elevator would be a great 1st stage. Just pointing out that it isn't everything.

The countermass must be above the geosynchronous altitude (like 36 000km from the earth surface, IIRC) to compensate for the entire cable length (and mass) that is below that altitude, and attracted to Earth.

Yep, the CG has to be at GEO

The idea for Mars' space elevator was to create a swinging motion to avoid its moons. However, this could be applied only for several big moons/asteroids, and not for some hundreds/thousands projectiles

> 10K tracked at this time + possibly several 10's of thousand more that are currently untracked but capable significant impact.

 

[imported_Hamzter]

Couldn't satellites over time be put into orbits would never collide with the cable? I don't really know anything about satellite orbits, I'm sure there's someone out there who knows. Also, how common would it be for a satellite to come within, say, a mile of the cable (with the number of satellites there are today anyway)?

I wouldn't have thought meteorites would be much of a problem, they'll probably just punch a small hole in the cable, so long as its designed well and happens when the cable is complete, it should make almost no difference to the strength of it.