How would anyone actually build a space elevator?

[Red Dwarf]

I see lots of stuff about what a space elevator would be made of, and all of the problems associated with making one. The one thing I haven't seen, though, is how to actually construct one. Can you just lower a winch down from geostationary orbit? How would that work?

[I.T Marcus]

If you mean a winch in the sense of a tug that pulls cargo up to the vessel then I would think not

If the any part of the destination vessel had to touch the atmosphere it would slow the vessel down, effectively de-orbiting it over time.... so what came to my mind is a really really tall tower with a pressurized cabin at the top..... kinda like a airship dock where the airship flies by really fast and you have to jump on before it leaves lol... but if you jumped on before reaching orbital velocity yourself then you yourself would slow down the craft and after each passenger you would have to fire an engine to sustain your orbit

Hope this was kinda what you were looking for if not, let me know and I'll try my best to help you!

Edited July 22, 2014 by I.T Marcus

[Seret]

Can you just lower a winch down from geostationary orbit? How would that work?

Well, no one really knows since no one has built one, but essentially yes. You'd launch a drum of cable and a lot of counterweight mass up to GEO. You drop the cable down to the ground (easier said than done), and anchor it there. Then climbers ascend reinforcing the cable, with more counterweight being added to the top as you go. Note that doing this would require a lot of conventional rocket launches and stronger materials than we know how to make, so it's still very much sci-fi.

Edited July 22, 2014 by Seret

[jwenting]

Better yet, capture a suitable asteroid and park it in GEO, build a factory for the tether on the asteroid, using the material of the asteroid as raw materials for the tether...

[Sky_walker]

The essential part is tether.

We can't manufacture any suitable material in quantities required for this sort of enterprise. Anything that we can build would tear itself apart under it's own weight.

Read: specific strength, "Breaking length" column, you are looking for something longer than 40 000 km.

Better yet, capture a suitable asteroid and park it in GEO

It needs to be behind GEO. We're talking here about over 35 786km.

If it'd be on a geostationary orbit - even a weight of tether itself would be enough to pull your asteroid down from the GEO. However if the asteroid is beyond GEO - it works as a counter-weight balancing whole system

Edited July 22, 2014 by Sky_walker

[Charzy]

Better yet, capture a suitable asteroid and park it in GEO, build a factory for the tether on the asteroid, using the material of the asteroid as raw materials for the tether...

You can't build ultra-strong cables from balls of rubble. The only material we know of that would work for this is carbon nanotubes, and they're really expensive right now, and you'd need an unholy amount of them.

[jwenting]

The idea is to capture a carbon heavy asteroid in GEO, weave nanotube tether both in and out, and have the counterweight be another 'roid in a higher orbit, reeling it out as the tether to the surface drops down.

Or that's the idea I've read in several books discussing realistic (technically, as compared to pure sci fi) ideas.

[ZetaX]

Read: specific strength, "Breaking length" column, you are looking for something longer than 40 000 km.

You need significantly less than 40000km of breaking length; the 6000km at the bottom are enough (but not enough if you throw in usability and security margins, not even speaking about the problems manufacturing this). Gravity and centrifugal forces are somewhat in favor of this, and additionally you can build it cone-shaped (or actually a more complex shape), i.e. the lower and upper end being thicker to support (or tether) all the stuff above.

[Red Iron Crown]

It needs to be behind GEO. We're talking here about over 35 786km.

If it'd be on a geostationary orbit - even a weight of tether itself would be enough to pull your asteroid down from the GEO. However if the asteroid is beyond GEO - it works as a counter-weight balancing whole system

I recall reading a plan to have the construction facility at GSO and ease out the counterweight as the cable is built or lowered. The counterweight could be another tether.

[magnemoe]

One plan was to launch an thin base cable to geo, then lower the edge down to earth, this will push the drum outward.

Then you have the edge at earth you send up spinners who increase the cable strength, you power them with lasers from earth

[Vilheim]

Something that has occurred to me as yet another engineering problem of building a space elevator:

The space elevator would have zero (or very close to zero) orbital inclination in order to be in GEO, right? So what about all the satellites in lower orbits that also have small inclinations? Without adjusting any of their orbits, they would be very likely to crash into the tether which would, to put it mildly, create problems.

We could fix some of this by adjusting the orbits of current active satellites to having a more significant inclination, reducing (but not entirely eliminating) the chance of a collision. But what about the inactive satellites and debris in low inclination orbits that we cannot control?

:/ That could pose a bigger problem than anything else when we finally do have the ability to mass-produce a material strong enough to build the thing in the first place.

[Red Iron Crown]

Something that has occurred to me as yet another engineering problem of building a space elevator:

The space elevator would have zero (or very close to zero) orbital inclination in order to be in GEO, right? So what about all the satellites in lower orbits that also have small inclinations? Without adjusting any of their orbits, they would be very likely to crash into the tether which would, to put it mildly, create problems.

We could fix some of this by adjusting the orbits of current active satellites to having a more significant inclination, reducing (but not entirely eliminating) the chance of a collision. But what about the inactive satellites and debris in low inclination orbits that we cannot control?

:/ That could pose a bigger problem than anything else when we finally do have the ability to mass-produce a material strong enough to build the thing in the first place.

I've read that you can make the tether oscillate like a guitar string to avoid collisions, but I have forgotten the details of how it would be controlled.

[ZeroTheAstronaut]

I've read that you can make the tether oscillate like a guitar string to avoid collisions, but I have forgotten the details of how it would be controlled.

Considering a lot of designs like flat strips of carbon nanotubes, and in the novel Limit they have two of those stripts, one could tug alternating between the two strips, causing tension to oscillate it one, then the other direction, all by pulling on it on the ground. Or even clever use of which cable you climb up with heavy cargo.

If it doesn't oscillate, every satellite in orbit WILL eventually hit it.

[KASASpace]

Simple, you don't. This is one of those ideas people think are good. But they aren't. Building a space elevator? The stress on the structure would be too much to bear for anything but carbon-nanotubes, and even then it's hard to tell. You would experience what makes orbits even possible, and that's the force created when rotating around a common axis, centripetal force. Many may, and may not know that this force keeps you in orbit. That's why orbits are the shapes they are. The elevator would have problems because the force applied is too uneven, it would end up getting pointed in the opposite direction of rotation if not perfect, and how would you maintain GEO? Satellites use engines, but a fixed structure can't change it's orbit. It would be cheaper to go to the moon, build a decent mining colony, and build what you want in space on an orbital fabrication facility with resources from the moon. We have the technology to do it, just not the will. You see, eventually the in-space resources will be so cheap to maintain that you just park it in a garage, "open the hood, find the problem, fix it somehow, and be on your way." Then, you could get the resources to the fab-fac easily.

Now, what would the cargo pod on the elevator be powered by? Electricity? Probably not, if you want decent sized payloads (~10 tons at the least) then you would need rockets still. So what's the point of the elevator? And what if you want a lower orbit. Wasted Delta-v.

So, no-go.

[Red Iron Crown]

Simple, you don't. This is one of those ideas people think are good. But they aren't. Building a space elevator? The stress on the structure would be too much to bear for anything but carbon-nanotubes, and even then it's hard to tell. You would experience what makes orbits even possible, and that's the force created when rotating around a common axis, centripetal force. Many may, and may not know that this force keeps you in orbit. That's why orbits are the shapes they are. The elevator would have problems because the force applied is too uneven, it would end up getting pointed in the opposite direction of rotation if not perfect, and how would you maintain GEO? Satellites use engines, but a fixed structure can't change it's orbit. It would be cheaper to go to the moon, build a decent mining colony, and build what you want in space on an orbital fabrication facility with resources from the moon. We have the technology to do it, just not the will. You see, eventually the in-space resources will be so cheap to maintain that you just park it in a garage, "open the hood, find the problem, fix it somehow, and be on your way." Then, you could get the resources to the fab-fac easily.

Now, what would the cargo pod on the elevator be powered by? Electricity? Probably not, if you want decent sized payloads (~10 tons at the least) then you would need rockets still. So what's the point of the elevator? And what if you want a lower orbit. Wasted Delta-v.

So, no-go.

You put some kind of thruster on the portion of the structure at GEO, that lets you do corrections and avoid obstacles, some have even suggested having the surface end of the tether connected to a ship at sea to give some maneuverability.

Foolish to use rockets for the ascent, electric power is the way to go. Payload per car doesn't matter that much as you can have a train of cars moving up and down the tether simultaneously. The transit times will be long, though, likely days to GEO. The point is to avoid delta v and the tyranny of the rocket equation.

Maybe carbon nanotubes can do it, maybe some other material we haven't discovered yet. Space elevators are much more feasible on the Moon or Mars, but it's hard to imagine enough demand to justify them anytime soon.

[KASASpace]

You put some kind of thruster on the portion of the structure at GEO, that lets you do corrections and avoid obstacles, some have even suggested having the surface end of the tether connected to a ship at sea to give some maneuverability.

Foolish to use rockets for the ascent, electric power is the way to go. Payload per car doesn't matter that much as you can have a train of cars moving up and down the tether simultaneously. The transit times will be long, though, likely days to GEO. The point is to avoid delta v and the tyranny of the rocket equation.

Maybe carbon nanotubes can do it, maybe some other material we haven't discovered yet. Space elevators are much more feasible on the Moon or Mars, but it's hard to imagine enough demand to justify them anytime soon.

Actually, electric power lifting that many tons? Not yet mind you. It would take enormous amounts of energy you just can't get with reactors on ships. Plus, you would need to find the ship.

What if the portion at GEO is not moving the appropriate speed? GEO is a type of orbit, not an altitude. If there were any counterweight it would most likely pass the speed on to the counterweight. Which means no portion actually AT GEO.

[SargeRho]

Geostationary IS an altitude, 35,786km above the equator.

[Red Iron Crown]

Actually, electric power lifting that many tons? Not yet mind you. It would take enormous amounts of energy you just can't get with reactors on ships. Plus, you would need to find the ship.

You have a car descending for each car ascending, or more precisely enough empty cars to mass close to the same as the ascending cars. Connect them so it behaves like an elevator and counterweight, much lower energy costs to as the change in potential energy is close to zero.

What if the portion at GEO is not moving the appropriate speed? GEO is a type of orbit, not an altitude. If there were any counterweight it would most likely pass the speed on to the counterweight. Which means no portion actually AT GEO.

The idea is that the center of mass of the entire elevator system is at geostationary altitude. The tether hangs below, the counterweight above. All parts have an angular velocity the same as the Earth's rotation, so the tether wants to fall downward and the counterweight upward, exactly balancing. The counterweight can actually be habitable space, it will conveniently have some centrifugal force to simulate gravity (the further away the counterweight, the greater this effect). Essentially the whole thing is a satellite at geostationary orbit with tremendous tidal effects.

[Rakaydos]

I believe Airship to Orbit (Perhaps supplimented with something like an external microwave powersource and a thermal rocket) has most of the advntages of a space elevator, and less (or at least, different) drawbacks.