Venus Space Elevator
This article suggests a non-standard design space elevator that is to be suitable for slow-rotating planets or moons. I came with the idea prior to I learned about very similar Paul Birchs Orbital Ring design suggested far earlier. However, I left my idea as simple as it originally was, virgo intacta :).
[ If I understood correctly, the only new idea above is the usage of the non-enclosed fast-rotating orbital ring torque to drag a cargo in the space. The lost energy would be refilled back to the ring by using linear motors on maglev carriages supplied by power cable extending from Earth surface. ]
A standard Space Elevator
You can find tons of information on usual design space elevators around the Web (check the Wikipedia for example). However the standard design is ingenious and simple enough that it deserves a brief description even on this site :).
A standard space elevator consists of an extremely strong rope anchored to planet surface (at some point along the equator) and of a counterweight fixed to other side of the rope. As the planet spins centrifugal force produced by counterweight keeps rope straighten. A wagon carrying cargo can then climb the rope to the outer space.
How long the rope? The counterweight revolves at the same rate as the planet. Obviously the counterweight must be placed beyond synchronous orbit to be able to pull on rope (otherwise it would fall to planet surface). Thus rope must be at least as long as is the height of the synchronous orbit for that planet.
How heavy the counterweight? It must pull on rope with force that at least matches the weight of the rope. If you place the counterweight only slightly beyond synchronous orbit it will have to be very heavy, however if you put it far beyond it can be much lighter.
This works well on Mars Mars rotates fast and is not very massive thus we dont have to make the rope long nor raise heavy counterweight.
Venus is a completely opposite story. It rotates slowly and is almost as massive as Earth. It would be impossible to build a standard space elevator on Venus.
The orbital ring Space Elevator
Now lets see what can we do about Venus.
The basic idea is simple. We will form a ring from a very strong rope and will place it in a low orbit around a planet. We will then force the rope ring to rotate much faster than the orbital speed as fast as possible concerning strength of the rope and centrifugal force. Once it rotates fast enough it will become quite rigid because of internal tension.
Now we have to connect the fast rotating ring to the planet surface by short rope fragments. At one side these fragments are anchored to planet surface (each one at one point along equator) but unfortunately the other side cannot be fixed directly to rope ring as it rotates much faster than the planet surface. Some sort of a slippery joint will have to be used!
Huh a slippery joint? Well, magnetic levitation as used in maglev trains seems suitable (I personally prefer a passive, induction type magnetic levitation). Hence, the rotating ring would act as a maglev train rail and some sort of levitation carriage will be suspended to it carrying an anchor rope. Of course, you noticed that a magnetic levitation uses energy and it really is an important disadvantage of such design.
On the other hand, using the maglev train technology of liner motors it is also possible to put energy into the rotating ring thus making it rotate faster (accounting for loses).
Another major problem is the stability of the rotating ring. The mathematic is beyond my knowledge (actually, I didnt even try) and I cant say anything about it. But being experienced in engineering field I bet that the ring will not be stable by itself (assumption that is always a safe gamble).
Okay, now we have a ring that is rotating in low orbit at super-orbital speed and we have anchor rope fragments that are hanging from the ring on maglev carriages and are anchored to planet surface. How do we use the space elevator?
First a wagon carrying cargo climbs one of anchor ropes up to the rapid revolving ring. Then the cargo is moved to an independent maglev carriage that can freely move around the ring (not the one that is carrying the anchor rope). The independent maglev carriage is then left to accelerate carried by revolving ring. Finally, when it gains enough velocity, the cargo is released reaching a higher orbit.
We know already what are disadvantages of such space elevator (complicated design, ring stabilization, energy loses, complicated cargo handling). Are there advantages?
Well, used on slow rotating planets it can be cheaper to build than a standard design space elevator. Further, it is easier to reach low orbits using this design (especially for de-orbiting). It can be used for fast transportation of goods and people within the planet. And finally, it can also be used to transport and store energy (in form of kinetic energy of the revolving ring).
Can it be used on Earth? I think yes (I would suggest placing it some 160km high) but I am not sure it can compete with more standard designs. If nothing else may become a problem, the need for cooperation of many countries around the Equator must be guaranteed to successfully run and maintain the ring type space elevator.
Can it be used on Moon? Yes, of course (I would suggest placing it only 5-10km high) but again there are more competitive designs.
On the picture bellow you have depicted two possible designs for maglev carriages. One that uses repelling magnetic force is more complicated. The other one, that utilizes attracting magnetic force is much simpler and has a nice feature that the carriage simply falls down to the ground if the anchor rope gets broken (because this will also break the power cable that is supplying magnets). I am not joking - I think that falling carriage is better option than carriage that is uncontrollably carried away by the rotating ring. Of course, in both cases the best option is to, I think, blast the disconnected carriage into pieces.
Danijel Gorupec, 2006