Space Elevator

[MolotovCocktail]

Anyone here have an interest in this subject? Basically, a space elevator is, well, an elevator that goes into space. The object or thing thats in space would follow a geosynchronous orbit (meaning it would orbit in such a way that it stays at the same point above the Earth), and things would be tethered to a rope made of some superstrong material (carbon nanotubes have been hypothesized).

 

here is a link for basic general info on it:

link: http://en.wikipedia.org/wiki/Space_Elevator

[Rocket Man]

i'm not sure anyone here wouldn't have some sort of interest in the subject (however apathetic we are)

 

as far as i can tell, the main problems are the tensile strength of the cable as the distance from a stable orbit increases, and sourcing the counter weight to tack on the end.

you've also got heaps of problems with atmospheric effects, a light wind would rack up tremendous forces

[insane_alien]

Carbon nanotubes have the tensile strength to hold the counter weight and a sea platform would be able to cope with winds and reduce the bigger problem of satelites. nothing would be worse that a big bit of spacejunk slamming into it.

 

on the plus side, if it did snap the the portion that falls to earth will mostly burn up. meaning the first 100km or so will just coil up around the baseand everything above gets vapourised.

 

another bad thing is that if it falls there will be a big rise in CO2 from the burning elevator

[Klaynos]

which is all well and good as long as you're not stood on the top bit when it breaks

[insane_alien]

depending on how far out the top bit is an where it breaks then you might not be coming back to earth. mos likely you'll just be left stranded in an elliptical orbit. if you are then you could probably use an escape system

[Sisyphus]

My major concern be space junk, small meteorites, etc. The "cable" (most likely a wide, thin strip of nanotubes or something similar) is basically a thousand mile long target which will most likely be bombarded constantly. It needs to be able to survive a lot of holes, and have a way of repairing them quickly and often.

[insane_alien]

is basically a thousand mile long target

 

try 36 thousand. these things will be MASSIVE if they're ever feasible.

[Sisyphus]

Yeah. I notice you said that a sea platform would reduce the problem of satellites. How do you mean? I've heard people talk before about the whole thing being mobile, to dodge the bigger junk. That doesn't seem like it would be all that feasible, though. I mean, the thing could move, but it seems like the delay in moving a 30 thousand mile long rope would be a long time, so you'd have to know well, well in advance that a collision would take place.

[insane_alien]

well, we already track all of the bigger bits of debris up there so it would be trivial to predict a collision and how to move it out of the way in time. although, even then it'll take a while and smaller bits will likely hit it. I'm going to go with by the time we can put up a space elevator we'll have the technology to get rid of the junk.

 

or lasers. you'll have plenty of solar power, chuck a couple of automated laser turrets on it every few kilometers. like the anti missile systems on ships.

[Phi for All]

If we can build one we'll build more than one. Wouldn't a series of these elevator towers replace the need for satellites? There's most of your junk problem gone.

[insane_alien]

Phi, i'm talking about the junk thats already up there. it isn't just going to magically disappear. either we go up there and collect it all bit by bit or we have ultra cool laser sattelites

[Sisyphus]

I don't think it would replace the need for satellites. A space elevator is an enormous engineering project and continuuing investment, bigger even than the ISS. A satellite launched via that elevator is a lot cheaper than even the cheapest sattelites now. If anything, there will be a lot MORE of them once we have functioning space elevators.

[insane_alien]

I don't think it would replace the need for satellites. A space elevator is an enormous engineering project and continuuing investment, bigger even than the ISS. A satellite launched via that elevator is a lot cheaper than even the cheapest sattelites now. If anything, there will be a lot MORE of them once we have functioning space elevators.

 

i'll agree with this. though, the new sattelites will be in a sufficiently high orbit so that they won't pose a threat to the towers ever.

[Phi for All]

Phi, i'm talking about the junk thats already up there. it isn't just going to magically disappear. either we go up there and collect it all bit by bit or we have ultra cool laser sattelites

Tired of ho-hum bungee jumps? Bored with BMX? Try Satellite Roping off one of the Space Elevators!!

 

I realize you were talking about what was up there. I think that replacing them won't be a problem because you'd have a bunch of towers to attach equipment to so there would be less need for satellites, wouldn't there? How many elevator towers would you need to provide global coverage? This assumes that such a massively expensive undertaking would be funded by many countries so that each could have equipment on every tower built.

[insane_alien]

yes it would replace them. and you'd need three at least. but then, the counterweights would attract each other which would cause quite a bit of instability and they'd fall down.

 

but the junk i was talking about would be the sattelites launched up to now that would still be in orbit when one of these things is (being) built. THATS the junk problem. Those are the ones going to be smacking into it at a couple of kilometers per second.

[MolotovCocktail]

I'm not so sure if other satellites would be much of a problem since we know where the path of their orbits are, its just a matter of building one that is not in the path of an orbit (or decommission them). And most of the garbage thats up there is small stuff such as lost items or wrappers or stuff that astronauts threw out.

 

I think that satellites would increase after one is built since it would be far, far cheaper to go into orbit than it currently is. Another thing that I was wondering would be how much cheaper and possible space tourism would be once a space elevator is built, since we would not be required to go through years of training nor would we have to sit in multi-million dollar space shuttles (Though I heard Virgin Galactic built a plane that could go 60 miles above Earth's surface, and its much, much cheaper than NASA).

 

Seriously, the possibilities are endless with a space elevator.

[Sisyphus]

And most of the garbage thats up there is small stuff such as lost items or wrappers or stuff that astronauts threw out.

 

The trouble is with space junk is that even the small stuff is dangerous, because the relative velocities are so large. One screw doesn't seem like much, but when it's moving several times faster than the fastest bullet, it can be quite dangerous, indeed.

[Rocket Man]

virgin galactic barely kisses the edge of space, it takes 30 times more energy to make an orbital instertion.

a sea platform would probably be the way to go, but think of the forces on a decent wind on 100km of cable. i'd expect they'd make it entirely orbital, fix a platform/elevator car on the end and hold the whole thing 100km above geostationary when it's not needed on the ground. with the amount of counter weight balancing going on you wouldn't need any form of propellants to shift the orbital.

[Velocity517]

Well the satellites would eventually get to be a bother, considering how many there are. If you chart all of their paths, you're bound to have tons of collisions eventually. Also, I think there's not gonna be AS many satellites, but as cheap as it'll be to launch them, people will shoot off a few. What about some sort of Huge anchor station on the planet, while the end of the elevator geosynchronously orbits earth, and you connect the supports and shaft when needed? I mean gravity would be problematic but it saves on material stress and weather problems.

Question 2, just out of curiosity, what happens when lightning hits the tower and is conducted out towards space?

[Rocket Man]

if you plot a geosynchronous orbit on a map of the world, you either have a dot on the equator or the satellite oscillates north-south.

 

they'll probably make the elevator car bouyant in water, drop it in the sea still on the end of the cable and rendezvous with a boat of some sort. that would be much cheaper and probably more reliable

[Sisyphus]

i'd expect they'd make it entirely orbital, fix a platform/elevator car on the end and hold the whole thing 100km above geostationary when it's not needed on the ground. with the amount of counter weight balancing going on you wouldn't need any form of propellants to shift the orbital.

 

I'm not sure exactly what you're describing. What does "entirely orbital" mean? A space elevator is a counterweight above geostationary orbit physically connected to a ground station by some sort of cable, which the "elevator car" can move up and down.

 

and you connect the supports and shaft when needed?

 

What supports and shaft? The whole thing is a cable.

 

Question 2, just out of curiosity, what happens when lightning hits the tower and is conducted out towards space?

 

That wouldn't happen. Lightning is a discharge between negative and positive charges, and so it can only be between those regions. The lightning necessarily is "used up" before it leaves the atmosphere.

 

they'll probably make the elevator car bouyant in water, drop it in the sea still on the end of the cable and rendezvous with a boat of some sort. that would be much cheaper and probably more reliable

 

Why would they do that? The elevator is connected to the ground. That's the only way it can work.

[Rocket Man]

that's not the only way it can work.

a crane is fixed to the ground... unless it's a blimp in which case it's still called a crane because that's the purpose it serves.

 

if it's not fixed to the ground, you need another method of supplying the upward force. interms of the elevator, this is called centripetal force.

so all the elevator is, is a crane held up by centripetal force.

it has a car which moves up and down a cable so it's called an elevator.

an elevator in a building isn't attached to the ground, it's attached to a building.

 

a blimp can act like an elevator, all you need is a winch on the blimp. if you move the whole assembly out of the atmosphere via orbital mechanics, you avoid the whole issue of docking stations. the car can be a floating docking station. the cable is held tight across it's orbital.

[SkepticLance]

As someone mentioned, carbon nanotubes are strong enough to form the space elevator. It would be a ribbon, wide enough so that if a minor piece of space junk flew through it, the hole would not break the ribbon. It would be 78,000 kms long. This permits it to be held taut by centrifugal force, with no counter-balancing weight at the end.

 

This is important if we use it as a means of launching a vessel going to the moon or Mars etc. The vessel can accelerate right up the full length of the cable and be flicked off the end into space at an enormous velocity, using only electricity for acceleration. Assuming the space elevator is built about 100 years from now, we will have magnetic-elevation technology to carry a craft up the ribbon at enormous speed. After reaching the 100 km mark - a tiny part of the total length - it will be in almost-vacuum and micro-gravity, meaning that acceleration and velocity could be tremendous.

 

The ribbon will be narrow at the extreme upper end, and very wide at the bottom.

 

Arthur C. Clarke wrote a book based on this idea - "The Gates of Paradise" - and suggested at the end the ultimate outcome. A thousand elevators, all connected in space, in a thousand years, by a tubular city all round the Earth - Ring City.

[Sisyphus]

Rocket Man:

 

In order to be able to support any weight, the counterweight has to be above geostationary orbit. If it is at geostationary orbit, it will stay in place, but any weight applied to it (which is the whole point) will drag it down. Therefore, the cable has to be attached to the ground and taut at all times, to keep it in place.

[Rocket Man]

if the counter weight is at geostationary, it isn't supplying any upward force. what supports the weight of the cable?

i agree with skepticlance and 78000Km, geostationary is about 24000Km. that's where the tension comes from. any part lower than geostationary is influenced primarily by gravity, any part higher is influenced primarily by centripital force. so you get a tension along the length of the cable.

it doesn't need to be attached to the planet, becasue it already has tension there, you can't supply an upward force to it from the ground because it will flex.

so why fix it to the ground at all? it's moving so slowly at ground level that you can accurately and reliably control it's vertical position from the counter weight at 78000Km. with those distances, pulling the cable 100Km higher is trivial.

if the car comes down and floats near the end of the cable, a rendezvous with a boat would again be a trivial matter because the drag from the water nullifies relative velocities.