Space people, get on this already!

[Unwardil]

Ok, so I've made a bunch of threads about this topic because I have a massive hardon for space elevators.

Trouble is, they're so incredibly impossible at the moment right? WRONG! Maybe....

There's this idea for a floating sort of space elevator, basically a really big sky scrapper that's held up with blimps. Cool, nifty thrifty, but it's only going to get you to the elevation of a weather balloon before you're right back to square one. All you've done is move the gas station closer to work, you haven't actually gone and built the high speed bullet train that leaves from your door (or, well admittedly snail powered train considering how long you'd be riding a space elevator to get into orbit, but ignore that).

I present to you, orbital cable car chains.

Yeah, sorry, I also have a hardon for low tech solutions to high tech problems.

So you simply build a network of cable car stations, but not ones that are on loops, they're on straight cables, where to lift cargo from the earth on one, you simply spool out the counter weight and let centrifugal force do most of the pulling once you're past the half way point, meanwhile a second straight cable car would be doing the opposite, letting the weight of the payload going down to earth do most of the work once it's past the half way point.

All you would need would be a way to get some form of ballast to attach to the counter weights at both the midway point or at the high orbit point respectively, some sort of asteroid being harvested and brought down to earth, perhaps.

Anyways, I'm pretty sure that because gravity is exponentially stronger the closer you get to the earth, we would actually have materials available now that would be strong enough to make a cable able to do what I'm proposing but what do the actual scientists think of this idea and it's feasibility/total unfathomable ridiculousness?


Edit: Forgot the most important part.

Obviously, because the system only drives it's self once the stations have passed the halfway mark, you would have some kind of generator being used as a braking system which would store the energy in some fashion to get them rolling again on the return trip. Not 100% sure what the best way to do that would be though, maybe in the form of some massive fly wheels which would be spun faster and faster to keep the inertia of the cable movement in check and would then be used to kick start the reverse journey. I'm admittedly sketchy on the physics of that, as I'm pretty sure the materials for something of that magnitude don't exist, plus there's the whole problem of things spinning in space and how that makes them change position etc. You could just as easily use rockets to kick start it and simply generate electricity from the braking.

 

[Netheralian]

I'm confused - can you draw a picture?

I don't think you have solved any problems here but i'll reserve any comment until I understand what you are actually saying.

 

[Demojen]

Not economically feasible.

Problems with this model.
Atmospheric pressure not taken into consideration, interference (weather), oxygen content, temperature...the list goes on.
It would have to be a no-fly zone, militarized and they'd have to spend a fortune in fuel keeping the cable at length without losing altitude. Any slack in the cable would create more tension on the metal with catastrophic results. The longer the cable, the less slack they can deal with.

It's just a big fat sink that requires way too much oversight, resources and money to maintain.

 

[Unwardil]

Well, I say cable, I really mean chain. Something that would have individually stiff components with links that could flex and stretch during acceleration and braking. Probably you would need some kind of maneuvering thrusters on each chain segment to keep the whole thing in alignment.

But mostly it's the idea that you could use the centrifugal force of the orbiting elevator station to act as your primary lifting drive. That's mostly what I'm sketchy on the physics about, or am I totally wrong about that?


Drawing wise... let's see here...

(Counter weight)-----------------------------(orbital station)-(Elevator) | (top of

(Counter weight)-(orbital station)---------------------------(elevator) | floating tower)​

Does that serve as a better visual? So as the one elevator goes down, the other comes up, keeping the whole thing balanced. Beyond half way, the centrefugal force is pulling the elevator up while gravity is pulling the return load down, canceling the two out.

 

[kenandkids]

I think that you have seriously miscalculated the enormous amount of fuel needed to keep something in constant place while dealing with atmospheric influences. It would spend all available fuel just to sit in relative place.

 

[Unwardil]

Well here's the thing about that.

Because the whole chain would be moving up and down, it would only enter the very edge of the atmosphere for brief periods of time during docking with the lighter-than-air tower. Most of the time it would be fully out of the atmosphere in high geosynchronous orbit, during which time, you could re-align the thing.

Obviously you would need some fuel to maneuver the thing, but you'd be able to lift cast amounts of fuel with every pay load no problem but if Ion engines were enough to keep it in place, you basically just need electricity which is plentifully available in solar form. Whatever gas it is that runs those things is very light and doesn't run out for centuries. They hardly produce any thrust, but in 0 g, 'hardly any' is still enough for a lot of things.

 

[)O( Hytegia )O(]

They hardly produce any thrust, but in 0 g, 'hardly any' is still enough for a lot of things.

... except maintaining a constant taught line whilst in Geocentric Orbit.

I don't know if you slept that day in Physics class, but energy is transferred when a line is pulled taught - it changes from whatever form it is into Potential Energy In this case it would require a constant stream of Fuel (Chemical) to keep a reverse motion (Kinetic) to maintain a line (potential).
You also forget that Orbit, unless it's speed is > the escape velocity of the Earth, it's nothing more than extended falling. And a geocentric orbit's speed < escape velovity of Earth.

 

[nemesiss]

the only thing that comes to mind is the manga Alita to explain the orbital elevator idea, though in this story its a bit more elaborate.

 

[devilsadvocate]

The so-called centrifugal force is F=mw^2r or F=mv^2/r where m = mass of the object, w = angular velocity of the orbit, r = radius of the orbit, v = velocity at the orbit.

Geostationary orbit is at altitude of ~ 53 000 km and not so surprisingly one orbit takes ~ 24 hours. This makes the velocity of the object ~ 3000 m/s and the radius ~ 60 * 10^6 m (altitude of the orbit from sea level plus radius of Earth 6378 km). Centrifugal force at this orbit for one kilogram of mass would then be:
1kg*(3000m/s)^2/(60*10^6m) = 0.15 newtons = Not very much.

I'm sure there are tons of other problems with this design, but the "centrifugal" force just isn't going to be enough unless a very massive object is at orbit relative to the payload and in this case the centrifugal force would be greater, but so would the force of gravity.

EDIT: I just read the original post more carefully and I'm a bit confused why would you need two cable cars? Wouldn't just one lift with counterweight be better? Centrifugal force at geostationary velocities isn't going to lift anything up, at the best it can keep things from not falling down. The real problem is of course that one needs a massive object at the other end of the rope to be kept on the orbit so that pulling of the payload adds minuscule amount to it's mass.


Hytegia, what if the orbit isn't geostationary, but at higher altitude where at the angular velocity of Earth the object would be escaping, kept in place by the rope? Intuition tells me this wouldn't work, seems like you're getting something for free (acceleration on the rope), but I'm too lazy to think why exactly.

EDIT2: Well I wasn't lazy enough after all. As long as I can figure out, it would actually work and you could get centrifugal force that's net-effect is bigger than gravity pulls downwards. The problem of free energy is just apparent, because the force would transfer from Earth's rotation slightly decreasing, in a bit same way Earth is accelerating moon at the expense of it's own angular velocity.

 

[Unwardil]

The reason for the two cable cars was so that you could meet half way and then trade out the pay load on one car onto the counter weight of another, thus giving more lift and getting stuff all the way clear of earth's gravitational field.

 

[)O( Hytegia )O(]

... getting stuff all the way clear of earth's gravitational field.

To clear Earth's gravitational field is relative to the mass of both Earth, and the object in question. Remember, the moon is still in Earth's Gravitational Field as well.

This entire idea is a physics mess - not to mention reentry stress upon the rails and the cart itself both leaving and entering the Earth's atmosphere.

 

[RigelKentaurusA]

all the way clear of earth's gravitational field.

I wonder what the costs would be involved for an infinitely high space elevator (not that the physics behind the concept aren't already a bit... stretched).

 

[Unwardil]

Well, clear of the earth's atmosphere such that small maneuvering thrusters would be adequate for say, flying out a huge mining ship to an asteroid.

If it turns out the stress of re-entry is too great, you could still use the same basic design and simply use disposable rockets to lift large objects from the top of the platform to the base of the cable car (which is what you'd end up doing during the intermediary stages of construction anyway). You'd be able to get much much larger and heavier objects into space if you started from nearly the top of the atmosphere instead of from the ground and once clear of the atmosphere, centrifugal force does the heavy lifting.


Actually, the more I think about it, the more I think you'd need a very long chain that doesn't actually move all that much with many sub-stations along the way where out bound traffic gets shunted to the line that was just inbound so that you'd zig zag up and down the line depending on which line was going up versus down. You could have a lot of the weight that's being shifted be just ballast so that the overall weight remains neutral, but you just keep shunting stuff back and forth so that the stuff you want getting to the top eventually gets there.

Does that make sense?

So you have 2 subway lines and 20 stations along the track. The train it's self is as long as 19 stations. 1 train runs northbound until it runs out of track, then it turns around and goes southbound until it runs out. The other train does the same thing, only at the opposite time. The platform for both trains is in the center, so anyone traveling northbound if they start at platform 1, gets off at platform 2 and gets on the other train, when train 2 starts it's return trip, you're 1 platform closer.

Now, if there was a constant number of people always on the train, the overall passenger load of the train would always remain the same, it's simply a matter of how the load is distributed, but anyone on the train can easily get to any of the stations.

 

[)O( Hytegia )O(]

Well, clear of the earth's atmosphere such that small maneuvering thrusters would be adequate for say, flying out a huge mining ship to an asteroid.

If it turns out the stress of re-entry is too great, you could still use the same basic design and simply use disposable rockets to lift large objects from the top of the platform to the base of the cable car (which is what you'd end up doing during the intermediary stages of construction anyway). You'd be able to get much much larger and heavier objects into space if you started from nearly the top of the atmosphere instead of from the ground and once clear of the atmosphere, centrifugal force does the heavy lifting.

You ARE aware that the Eart spins so fast that it creates a Space-Time vortex around itself, right? o.o

 

[Unwardil]

Yeeees, but what does that have to do with a space cable car? I get that due to the length and speed of orbit there will be stresses placed on the system, but would they be insurmountable to currently available materials?

 

[)O( Hytegia )O(]

Yeeees, but what does that have to do with a space cable car? I get that due to the length and speed of orbit there will be stresses placed on the system, but would they be insurmountable to currently available materials?

*Facedesk*
No. But it's not even a probability. The rotation of the Earth is not enough to keep a constant, Geocentric orbit - of which to maintain would require a rotation that is equal speed to that of the escape velocity. No more (if it was spinning that fast, nothing not attached to the planet could stay on it) and not to slow (the Geocentric orbit would not be constant and would have to be maintained).
And, even then, the further you go away from an object in motion the more you lag from it's own motion, generally. Especially with a non-rigid object such as a chain. Even the slightest drag would be catastrophic for the entire proposition...
It's not even worth doing the math over.

 

[Unwardil]

Alright then, don't put it in geostationary orbit. Have it orbit slower than the earth. That wouldn't make it useless, it would just mean you would always require a rocket to launch from the top of the floating tower to dock with the #1 station on the cable car line.

 

[)O( Hytegia )O(]

Alright then, don't put it in geostationary orbit. Have it orbit slower than the earth. That wouldn't make it useless, it would just mean you would always require a rocket to launch from the top of the floating tower to dock with the #1 station on the cable car line.

*Facedesk*

Okay.
Take a jump rope. Walk outside, and spin so that it is taught straight out in front of you - this is geostationary. Now, suddenly spin FASTER.
After you're done tripping over yourself, untying the coil of rope wrapped around you, and puking up last night's dinner, tell me what conclusions you have drawn from this small-scale experiment on rotation of why a geostationary orbit is required.

 

[Unwardil]

No, it doesn't have to be geo stationary because the cable car isn't physically connected to the earth and it doesn't reach down into the atmosphere. It's like a fluid transmission, the fluid can be spinning faster than what it's driving and it still works. If you're using short ranged rockets to get stuff up to the lowest orbital station, which would be positioned beyond the atmosphere, you could actually have the whole thing curl back into a spiral and use the gravity of say, the moon to act as the driving force on the counterweight end. Remember, the two sides only have to oscillate back and forth a little bit relative to the whole in order to wiggle something from the bottom to the top.

It's even possible that if you made the whole thing lose enough, that the overall length could remain the same at all times and just wave form fluctuations along the length of the two chains would be enough to facilitate transport along the line. The whole thing is going to expand and contract anyways right? Why not make use of that dynamic? As one line is bunching at one end, make the other line bunch at the other end. You simply attach the payload to whichever line happens to be going the direction you want at the point in the line where you happen to be.

Edit: Holy crap holy crap, forget the centrifugal force thing.

You could do it with expanding gases alone!

What do you have a shit ton of in space for the taking? Solar radiation, heat. Use that heat to drive pneumatic pistons in the sections of the chain so that you can have the entire chain expand and contract, pushing against it's self. While one chain expands, the other contracts at various points along the chain so that you get the same oscillating effect between stations, which would themselves act as a kind of anchor for the chain. Then the only problem becomes heat dissipation but a heat sink array at sub junctions would be pretty easy to do, I should think. We already have supper conductor materials used in nuclear plants for doing just that.

 

[)O( Hytegia )O(]

Draw us a picture. I'm being totally serious - because I can't picture your idea of a "Space Elevator" being Feasible.