I was amazed to see my local TV news anchors discuss, and run a report on, the feasability of the space elevator, just a couple of days ago. I don't think a space elevator is going to happen any time soon, if ever, for one reason: everyone is focusing on the ability to stretch the "elevator" ribbon via a counterbalance extending beyond the geostationary orbital distance, and the amount of energy needed to lift the payload to the geostationary height -- but, it seems that no one is paying any attention to the amount of energy required -- or, the torsional strengh necessary to withstand -- to accelerate the payload to its horizontal (or "circular" or "orbital") speed.
It's not just a matter of lifting yay many pounds yay many miles straight up. That would only be the case if the Earth wasn't spinning. But, it is.
It will take quite a bit of energy to accelerate the payload "sideways" from a relative standstill (IIRC the rotational speed at the equator is about 1,000MPH) to the tens of thousands of miles an hour required to maintain a geostationary orbit.
Sure, it looks like a geostationary satellite isn't moving -- but it actually is moving, and at a very decent clip.
The reverse is also true when descending from orbit. All that rotational speed will have to go somewhere, and the stuff I've seen proposed, i.e., carbon ribbons, have tremendous strength in the "lengthwise stretch" department, but are very weak in any other direction.
Picture an ice ballet skater spinning, with her arms outstretched, and then pulling her arms inward. Notice how much faster she spins, as the rotational energy from her outstretched arms is translated into increased RPM as they move inward?
Now, imagine that her arms are 40,000 miles long, and each hand weighs a few tons, and tell me how much sideways force that "elevator" ribbon will have to absorb (and brake) as the payload, weighing several tons, traveling at several tens of thousands of miles per hour, descends to sea level -- with all of that sideways momentum having to go "somewhere" (i.e., cargo pressed against one wall, payload "car" pushing against the elevator ribbon).
I just can't see it being practical, and I doubt that the proponents have "done the math" on it.
