Another Space Elevator Concept

[TheFaithfulStone]

Hey, it sounds pretty similar to the space fountain.

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

Space fountains are cool because they can be anywhere, not just at the equator, they don't have to go all they up to GEO, and they don't require unobtainium cables. (It's debatable whether SWNT have the necessary tensile strength. I bet they do - but not yet.)

Also, the idea of the Loop is suggested on Wikipedia, but there's no reference to whose idea it is. It requires a tensile strength on the cable of 62.5 GPA. BUT - the thinner cable you suggest requires a tensile strength of 130 GPA. Most SWNT top out around 30-50 with a maximum theoretical limit of around 120.

Cool idea though.

Accelerating at two G's would let you reach escape velocity 3,000km up. But how would you climb a space fountain?

TFS

BTW, that's my quote! I'm flattered.

[Kayra]

You know.. it never ceases to amaze me how often I open my mouth before doing sufficient research

Wiki Touched on almost everything I stated here.

Even the idea I was toying with of having multiple segment loops was noted. Using larger tether only where required.

I still believe this would be the best way to go. All of the points I made in the first few posts are still salient. 3 especially of note are
1) Continious ability to monitor and repair the cable at ground level
2) Powering the system efficienctly from ground or space
3) Redundancy. If one side of the tether breaks, simply clamp the cable at both ends. rewind the tether until the base station is holding one end. Capture the other end.. and repair.

[Jay-qu]

Originally Posted by Pyrotex

Errr... I may have gotten the words reversed, too. I'll have to look them up.

I think that you may have! With the human spinning with buckets analogy, the buckets have a net force radially inwards, the bucket feels like its pulled out because it has a reaction force to your hand holding it and likewise the water on the inside of the bucket 'feels' like its pushing out but its just the reaction force to the bottom of the bucket.

With this conveyer belt idea, what is holding the cables ie stopping them from falling down - I suppose the satellite, there is no way the satellite could counter such a large force, unless it had some constat means of propulsion on board..

[Kayra]

What is holding it up should be the centri**** force from the counterweight at 62,000 miles distance from the earth.

The counterweight is actually the bucket in your anology.

[Jay-qu]

That wont work, the reason things end up in orbit is because they are spinning around the planet - there is no outward force, only an inwards.. Trying to haul something up would result in pulling it back down to earth IMO

[Kayra]

Hmm.

I have far to little knowledge of the math involved in orbital mechanics to argue difinitively that it will or will not work. I have a tendancy to visualize things things. hile this often serves me well, it just as often gets me in trouble. Especially when trying to understand most aspects of quantum mechanics.

This is how I visualize the orbit of an object. Please feel free to correct my misunderstandings.

When an object is in a stable orbit around a planet, that means that its velocity is exactly enough to counter the force of gravity. since its velocity is at a right angle to the force of gravity, it is in a state of constantly falling into the planet, and constantly moving away. Hence, no gravity.

If you slow the object down, it will decend to a lower orbit until it is again stable. The opposite occurs if you add velocity to it.

If you were to increase the velocity, but prevent the object from moving to a higher orbit, it would pull against what was preventing it from moving.

The counterweight is such an object, and the tether is the what is preventing it. The farther out the counterweight is, the greater it's velocity is, and the stronger it will pull in order to stabilize it's orbit.

Ugh. It is 2:30 in the morning and I need to sleep. I hope my ramblings made sense. (they always do to me )

[TheBigDog]

Originally Posted by Pyrotex

At the bottom end of the cable, you only need to support the elevator.
10 Km up, the cable needs to support the elevator AND 10 Km of cable, which may equal the weight of the elevator. At some point, you need to double the "thickness" of the cable to support the weight of all the cable below.

100 Km up, the cable needs to support the elevator AND 10 Km of 1-strand cable AND 10 Km of 2-strand cable AND 10 Km of 3-strand cable AND 10 Km of 4-strand cable AND 10 Km of 5-strand cable AND...etc.

You lost me here Pyro. The cable is being stretched, not compressed. So the tension should be equal over the whole length.

But wait... because it is vertical the top is not only under tension, but also supporting the weight of everything below it. Now I think I get it.

I am personally doutful that it can be engineered. The stability issues during the process of erecting the thing would be daunting. Assuming that you had all the materials, how would something like this get built?

Bill

[Kayra]

Originally Posted by TheBigDog

I am personally doutful that it can be engineered. The stability issues during the process of erecting the thing would be daunting. Assuming that you had all the materials, how would something like this get built?

Bill

Which stability issues? There are likely to be many, and I suspect each can be mitigated or eliminated through proper design and engineering.

I described one method on the first page (in VERY simplified form), and I am certain there are others.

To put in perspective what the material we require for the tether is capable of:

A typical sewing thread thickness Carbon Nano Tube (CNT) is capable of supporting a medium sized vehicle. A 5 KM stretch of the starting cable would weigh something in the order of 1 Kg.

Someone with some math skills might want to jump in at this point and extrapolate on these base values

[Kayra]

Here is a question for the physics folk.

The system would likely have a reduced cargo capacity due to the fact that the cable needs a consistent diameter for it's entire length.

Since it is powered from the ground, space, or both, would it be likely to meet or exceed the capacity of the other designs simply due to its ability to loft cargo at a much higher velocity?

One method of reducing startup strain (loading a cargo pod onto the system)on the cable would be by using a capstan type system similar to that used on a reel to reel tape, it would be possible to keep the entire cable moving at high speed, while stopping a small part of it. While stopped, the cargo pod could be attached, and then accelerated up to the cable's speed.

In space, the cargo pod could release itself before it reaches the platform, with enough momentum to ensure it reaches stable orbit. Going down, it would use the cable as a guide as it fell. Acceleration from gravity would allow it to catch up to the cable velocity, at which point it could clamp back down.

I am not certain how to handle the tricky part of undocking an empty cargo pod. Any suggestions there?

[Jay-qu]

I stick with what I said earlier: hanging anything from a satellite is going to just pull the satellite out of orbit.. I just cant get my head around having all the weight suspended from a satellite and it not having any effect on its motion..