Revolutionizing Space Travel: The Potential of Dual Space Elevators

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Discussion Overview

The discussion revolves around the concept of dual space elevators as a potential solution to the challenges of constructing a traditional space elevator. Participants explore the feasibility of using two elevators positioned on opposite sides of the Earth, connected by a cable that wraps around the planet, to mitigate the weight issues associated with the cable.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests that building two space elevators could neutralize the payload on the cable, allowing for the use of more traditional materials like kevlar.
  • Another participant questions how the proposed design would neutralize the payload, emphasizing that gravity would still exert a downward force on the cable.
  • Some participants argue that the idea of a cable wrapping around the Earth would not alleviate the tension issues inherent in constructing a space elevator.
  • There are claims that the engineering challenges of the dual elevator system may be greater than those of a single elevator.
  • One participant proposes that counterweights in fixed orbits would reduce the tension on the cable, although others challenge this notion, stating that the weight of the cable itself still needs to be supported.
  • Speculative ideas, such as drilling a hole through the Earth, are introduced but met with skepticism regarding their practicality.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the feasibility and implications of the dual space elevator concept. There is no consensus on whether this approach would effectively address the challenges associated with building a space elevator.

Contextual Notes

Participants highlight limitations related to the assumptions about gravity, tension, and material properties, as well as the unresolved engineering challenges posed by the proposed designs.

FXForLife
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Hello

I am new to thinking about these kinds of things so please forgive me if what I suggest is pure nonsense LOL!

As I understand it the main problem with building the traditional model of a space elevator is a practical one based on the difficulty in manufacturing a cable made of nanocarbon which can support its own weight below geostationary orbit.

Perhaps there is a way around this. Perhaps we can develop a model which reduces, or nearly eliminates the payload on the cable.

If we were to build 2 space elevators, one on either side of the Earth in perfect balance, with a land and ocean based cable circling the Earth and connecting the two, wouldn't that neutralize the payload on the cable? That way we could possibly construct the cable out of more traditional materials, like kevlar??

Thanks
 
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How would that neutralize the payload? Gravity is pulling down. A cable pulling sideways would not help anything. And I don't think you appreciate how big the Earth it. A cable long enough to go all the way around the Earth to connect two elevators in the air would sag till it touched the Earth and snap under its own weight in the process.
 
chrisbaird said:
How would that neutralize the payload? Gravity is pulling down. A cable pulling sideways would not help anything. And I don't think you appreciate how big the Earth it. A cable long enough to go all the way around the Earth to connect two elevators in the air would sag till it touched the Earth and snap under its own weight in the process.

Thanks very much for the reply.

I was thinking the two space elevators would be exactly opposite from each other, on either ends of the Earth so that the effects of gravity and centrifugal force would be in equilibrium.

The cable would wrap around the Earth on the ground, not in the air and shouldn't snap due to the equilibrium of the system (I'm trying my best here lol). If the circumference of the Earth is 40,000 km we would be adding, from what I understand, about 20% more cable, which, if made out of something other than carbon nanotubes, might very well be feasible.
 
Last edited:
Welcome to PF!

In equilibrium may mean all forces sum to zero, but it doesn't mean the forces go away. A space elevator would on its own be in a similar equilibrium to what you describe.
 
russ_watters said:
Welcome to PF!

In equilibrium may mean all forces sum to zero, but it doesn't mean the forces go away. A space elevator would on its own be in a similar equilibrium to what you describe.

If I understand correctly a space elevator on its own would still require a cable that could support its own weight below geostationary orbit.

But if you have two counterweights on opposite sides of the Earth, out in space, connected, then this is no longer an issue and a cable can be made of more typical materials.

thanks for the welcome btw!
 
Here are some diagrams to help explain my thinking:
 

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Oh, we understand your way of thinking alright. What we are telling you is that you are "solving" a little problem by making a bigger one.
 
I suppose if problem A is solvable in 100 years and problem B is solvable in 10, then problem b would be smaller.
 
FXForLife said:
I suppose if problem A is solvable in 100 years and problem B is solvable in 10, then problem b would be smaller.

Problem B is not solvable in 10 years. It's even more of an engineering challenge than a single elevator.
 
  • #10
If you have 2 equal teams playing tug-of-war the forces on the rope are equal and opposite so the total force on the rope is zero. That's why the rope does not move. That does not mean that the tension on the rope is zero. The situation you are describing is similar. The problem with building a space elevator is making a rope that will withstand the tension.
 
  • #11
mrspeedybob said:
If you have 2 equal teams playing tug-of-war the forces on the rope are equal and opposite so the total force on the rope is zero. That's why the rope does not move. That does not mean that the tension on the rope is zero. The situation you are describing is similar. The problem with building a space elevator is making a rope that will withstand the tension.

OK but the main difference here is that the counterweights are in a fixed orbit in space around the Eath and therefore they don't pull very much on the cable, they simply keep it in place.
 
  • #12
Drakkith said:
Problem B is not solvable in 10 years. It's even more of an engineering challenge than a single elevator.

Why?
 
  • #13
FXForLife said:
OK but the main difference here is that the counterweights are in a fixed orbit in space around the Eath and therefore they don't pull very much on the cable, they simply keep it in place.

The only difference is the useless rope around the world.
 
  • #14
DrStupid said:
The only difference is the useless rope around the world.

:eek: *carry the 2 LOL!
 
  • #15
FXForLife said:
OK but the main difference here is that the counterweights are in a fixed orbit in space around the Eath and therefore they don't pull very much on the cable, they simply keep it in place.

Each tether still has its own mass and, hence, its own weight which needs to be supported by the tension in the rope. This applies however many tethers are involved and is the reason why the space elevator is not yet doable.
 
  • #16
FXForLife said:
OK but the main difference here is that the counterweights are in a fixed orbit in space around the Eath and therefore they don't pull very much on the cable, they simply keep it in place.
This simply isn't true. In both cases, the counterweights support exactly the same weight: The weight of the cable from the counterweight to the ground. Your case has the added issue of a cable around the Earth that since it is parallel to the Earth's surface is supporting no weight at all. The added piece of your idea doesn't actually do anything at all.
FXForLife said:
:eek: *carry the 2 LOL!
Uh huh...in that cable around the earth, where it meets the space elevator: what direction is the force on the space elevator? Up or down?
 
  • #17
mrspeedybob said:
If you have 2 equal teams playing tug-of-war the forces on the rope are equal and opposite so the total force on the rope is zero. That's why the rope does not move. That does not mean that the tension on the rope is zero. The situation you are describing is similar. The problem with building a space elevator is making a rope that will withstand the tension.

What if we drill a hole through the Earth? Would that help anything? :smile:
 
  • #18
FXForLife said:
What if we drill a hole through the Earth? Would that help anything? :smile:

No, because the outer core is very hot and molten. Nothing is going to survive going through there, and the inner core is solid nickel / iron you ain't going to drill through that

Dave
 
  • #19
FXForLife said:
What if we drill a hole through the Earth? Would that help anything?

Layering impractical idea upon impractical idea will not lead to a solution. It also pretty much defines "overly speculative".
 

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