Consequences of Space Elevator

[SkepticLance]

Just reading up on this subject. Wiki has some good articles.

 

Quick recap. The space elevator is speculated to be a way forward in space travel. A ribbon shaped cable is hung from stationary orbit, and extends down to Earth. At the same time, another cable runs out into space for balance by supplying centrifugal action to hold the whole system taut. Special carriages ride up the cable into space, using electricity for power. This will cut the cost of launch into orbit massively.

 

A space elevator out from Earth would start at the equator, and be 36,000 kms long to stationary orbit. The second part would go another 36,000 km further out, unless a substantial weight was on the end, providing the 'swinging stone on a string' effect.

 

To get people up an elevator requires either massive radiation screening, or a very fast transit method - possibly magnetic levitation.

 

A space elevator from the moon can be organised also, but has to go to the La Grange points rather than stationary orbit. This means an elevator almost twice as long as the Earth one, but has two advantages.

1. It does not have to go from the equator - from the moon's pole is possible, where there is more likely to be water for a moon dwelling, and permanent sunshine for solar power.

2. Due to lower gravity, it can be much lighter in mass, and less strong.

 

A space elevator to Mars can be only 40% of the length of the Earth one due to lower gravity, and much less massy.

 

I can see the possibility one day of all three elevators being set up, and a constant stream of traffic from Earth to the moon and back, using an ion drive 'ferry'. Earth to Mars and back is more difficult. However, it is theoretically possible to put a very large space vehicle into an orbit that swings from Earth orbit to Mars orbit and back, passing close to both planets. A smaller space craft would have accelerate to intercept at each end of the journey. The advantage would be a very large space habitat (space hotel?) for most of the trip (six months) with all the benefits of comfort, sanity etc., and only a small craft needed to accelerate to speed, with savings in fuel and reaction mass.

 

How would this technology affect the future of humanity?

[Mr Skeptic]

Just wondering, what will power the space elevator? I've heard of an attempt to climb a short distance (40 m??) on a tether, with a power source designed to mimic one on a space elevator, but it was quite a failure.

[SkepticLance]

To Mr Skeptic

I have never actually seen that as a problem. I always envisaged cables (possibly superconducting) carrying electricity up and down the ribbon. As far as the original source of power goes, it could be anything from a nuclear fusion plant (remember that this technology is still well in the future) to giant solar panels placed on the stationary orbit portion of the elevator. For that matter, you could have solar panels sticking out of the elevator at almost all altitudes.

 

To me the big problems are

1. Developing the technology

2. Getting the funding to put up the elevator in the first place.

[Realitycheck]

It seems that the centrifugal? force of 30,000 km of cable spinning with the earth will not be enough to hold up the weight of the immense mass of the cable that is affected by gravity. It will simply pull itself out of orbit ... very easily.

[Mr Skeptic]

Ah, but a space elevator is very long. Hence, even with little resistance, after a while it would add up. So, you'd have to use either extremely high voltage, or a superconductor. To use the high voltage, you would need an insanely thick insulator, and to use a superconductor, you will need to cool it. Either way, you are adding a lot of weight, which would require you to build a much thicker cable.

[insane_alien]

It seems that the centrifugal? force of 30,000 km of cable spinning with the earth will not be enough to hold up the weight of the immense mass of the cable that is affected by gravity. It will simply pull itself out of orbit ... very easily.

 

 

thats why you capture a small asteroid and use it as a counter balance.

[Sisyphus]

It seems that the centrifugal? force of 30,000 km of cable spinning with the earth will not be enough to hold up the weight of the immense mass of the cable that is affected by gravity.

 

And yet it is. Math doesn't lie. You just have to extend it beyond geostationary orbit.

[Realitycheck]

I would like to see the plan for negotiating this cable in and around all of the space debris that it comes across. One little ding and, uh oh, it's not traversable anymore. It's got a kink in it. 30,000 km of space junk.

[SkepticLance]

To agentchange

You are correct in saying that a 30,000 km long elevator would simply fall. Stationary orbit is about 36,000 km above the equator, and (without a counterweight) the elevator would need to be about 78,000 km long for centrifugal action to hold it taut.

 

You are also quite correct to mention the problem of space junk. That is one reason why the elevator has to be a ribbon rather than a cable. It has to be wide enough to take a whole lot of 'bullets' making holes in it without the whole thing breaking. The normal design is a ribbon that is very wide at the central, geostationary orbit point, and tapers down to a much narrower ribbon at the Earth's surface, and at the outer limit.

 

I like the idea of a very long ribbon with no counterweight, since (assuming a magnetic levitation propulsion) that permits a space vehicle to accelerate the whole length of the 78,000 km and be released into space at high speed. This means that a space vehicle can be 'flicked' to Mars or the moon using only electricity for power. I would imagine very high velocities could be attained in this way.