Another Space Elevator Concept

[Kayra]

This seems so simple that it is likely to have been proposed here before.

If so, just direct me to the thread and I will be quiet

I see so much effort in the current SE developement going towards a climber, and method for powering it.

Why?

Would it not be simpler to simply create an SE using a loop of cable rather then a single strand? Certainly, the costs of the cable would be double, but the savings elsewhere might suprise us. The loop itself would not have to be the entire length of the tether, but only up to LOE or Geo orbit.

Having the loop allows for the following.

1) Redundancy in case the cable breaks: Simply clamp down on the remaining cable.
2) a means of lifting cargo on a continious basis. no waiting for a cargo pod to return.
3) the ability to power the lift from the ground.. or more importantly.. from space. ( assuming a solar power generator is built in space )
4) the ability to transfer energy generated in space to the ground with near 100% efficiency.


I am just wondering if I have missed some fundamental problem with this concept.

[Kayra]

Drat
5) Continious monitor and repair of the entire length of the tether, which should allow for a reduction in its cost. (massive redundancy for fault tollerance purposes would not have to be built in.)

any others I missed?

[Kayra]

<Sigh>

6) Drastic reduction in the weight of the lift pod as there is no engine aboard. This would allow larger cargo capacity.

[Kayra]

1. Build space platform and launch into geosync orbit
2. Loft sections of cable up to platform.
3. Platform lowers cable to earth.. adding sections as required.
4. Build earth platform
5. Capture cable from space platform and dock with earth platform
6. Earth platform adds new sections to cable
7. Space platform pulls cable up one side, and lowers it down the other side.
8. Capture other side of cable and dock it with earth platform
9. Fuse both ends together, forming a loop
10. Earth platform spins loop
11. Earth platform continuously adds thickness and width to the cable until desired characteristics are achieved.
12. Build space solar generator and launch next to space platform
13. Connect generator to platform. Now the platform can spin the loop and raise cargo.
14. If cable is not under full load from cargo, excess capacity can be used to generate electricity on the ground platform.



Did I miss anything important?

[Pyrotex]

Originally Posted by Kayra

1. Build space platform and launch into geosync orbit...Did I miss anything important?

Kayra,
brilliant idea, no kidding. I'm not SURE why this idea has not been touted before, but I have an idea... This is not to shoot your concept down, but to answer your question if anything was missed.

The SE "cable" (whether it be "spaghetti" or ribbon) will be under a huge amount of tension, as the Earth's gravity is pulling at one end and the other end is attached to a large mass that must orbit the Earth at a speed GREATER than orbital, in order to generate a balancing centripedal force.

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.

At the bottom end, the 1-strand cable may actually be no thicker than scotch tape or spaghetti. But by the time you get to Geosynch orbit, the cable will have to have hundreds, perhaps thousands of strands all "cabled" together. It may be one meter thick! And totally incapable of bending, of course.

Running this like a conveyor belt through "pullies" may not work. As soon as the thick part got close to the Earth, the thin part at some very high altitude would snap. IMHO.

[Pyrotex]

Extra Notes:
There is no such thing as "getting out of Earth's gravity field". It extends forever, it just keeps getting weaker and weaker. The Moon is IN the Earth's gravity field. That's what keeps it in orbit about us. So....the weight of the cable does indeed increase in a fashion that requires additional strands to support it.

However, having said, the gravity of Earth DOES decrease. So, let's say, at 1000 Km, you have to add an additional strand after every 12 Km, instead of 10 Km. At 2000 Km, you have to add one every 15 Km. Etc.

On the other hand, the increase in the number of strands must increase somewhat like compound interest. The next strand must support the strands added to support the strands added to support the strands added to support the strands added to support...

So the number required at Geosynch, where the tension is greatest, may well be enough to create a very thick "cable".

[Kayra]

Hmm, Lets see.

The Cable should end up being under precisely the amount of tension required to support it's current load plus itself.

The Space Platform is anchored in geo orbit by the length of the looped part and so should not add any "weight" to the system, while the counterweight is tethered in a higher orbit with a single cable.

As you increase the load on the cable (put cargo on it and lift it up) you can extent the length of the anchor cablle connected to the counter weight until it perfectly counters the cargo weight.

I did not think the space teather concept would not have been possible from the start if the cable did not have physical properties that allowed it to at least support itself, as well additional cargo.

[Kayra]

In thinking about it, I think the cable would get lighter as it approached Geosynchronous orbit (Approx 22,000 miles), regardless of it's size, as centrifugal force would counter it's weight.

The weight would again increase as it moved out to the location of the counterweight (Approx 62,000 miles). That single, unlooped cable may have to increase in size, but that should not be relevant to the looped side.

Or?

[Pyrotex]

Originally Posted by Kayra

In thinking about it, I think the cable would get lighter as it approached Geosynchronous orbit (Approx 22,000 miles), regardless of it's size, as centrifugal force would counter it's weight....

You are assuming that the cable thickness would decrease as gravity decreases.

The tension in the cable is not determined by just the local force of gravity. It is determined by the force of gravity (and the centripedal force) on every INCH of the cable from beginning to end. My point in my last post was to show that the tension on the cable is NOT a constant. The tension increases as you go "up" the cable so the cable must get thicker.

Even though the centripedal force is opposite and equal to gravity at Geosynch, that does not mean the Tension on the cable is zero. Rather, the Tension on the cable is the SUM of the gravity in one direction PLUS the C.force in the other direction.

If two guys grab your arms and both pull in opposite directions, the tension on your arms and body is NOT ZERO just because their forces are opposite and equal.

[Kayra]

Sorry if it appeared I was stating that the cable tension would be reduced to 0.

I was trying to say that the increase in weight you mentioned might not occur at the rate you specified, which might allow for a cable of a single width to be used. If a single width cable capable of supporting itself and cargo can not be used then the entire concept of a conveyor belt system ( I like the anology) will not work.

At no point did I assume that the cable would decrease in thickness with height. Sorry if I left that impression