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Saturday, September 15, 2007

Space Elevator

I don't think we will see a space elevator any time soon. Too much material would have to put in orbit, and we don't have a frequent flyer to carry the load. We can put bits and pieces up there, but the space program has not been getting the funding it needs to step up to the task. But eventually, say in a hundred years or so, we may get around to it. Sooner if it looks like someone from Asia is close to acquiring the capability. That could be China, Japan or India.

When someone gets around to putting one up, I am thinking we might want to use multiple strands separated by feet or meters, and we would want to be constantly renewing them. Any strands connecting a satellite in geo-synchronous orbit to the earth would be under constant assault by orbital debris. I see no way of protecting these thin strands from impacts with bits of old spacecraft, so we are just going to have to deal with constant degradation and periodic failure.

I envision having multiple strands that loop around pulleys at the top and bottom. You might have ten, a hundred or even a thousand strands of carbon fiber ribbon. The pulleys would drive the elevator and would constantly be feeding new strands into the mix and pulling old degraded and/or broken strands out. Elevator cars would latch onto all of the strands going up and be hauled to orbit. If one strand out of 100 fails, it will be no big deal. When cars reach the station, the could release their grip on the upward bound strands, transfer their cargo and then latch onto the downward bound strands. Mechanical engineers will have a field day with this.

Ideally, we would be able to generate new ribbon strands at the same velocity that the elevator travels, maybe 200 mph. If we cannot do that, we will need to be generating several strands and then splicing them end to end. That is going to be a good trick.

Getting this whole thing started is going to be a project in and of itself, but we manage to get ocean going ships going. How much is a space elevator going to weigh? Say a carbon fiber ribbon weighs one gram per foot. Then a mile of ribbon will weigh about ten pounds (5,280 feet per mile divided by 454 grams per pound). 25,000 miles of ribbon would weigh 250,000 pounds or 125 tons (2,000 pounds per ton). I think some railroad locomotives weigh almost that much. Big trucks fully loaded weigh 40 tons. Of course I could be off on my weight estimate by an order of magnitude either way, but I think it is something we can deal with.

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