Hank.Walker@CMU-CS-VLSI.ARPA (11/04/83)
Think of a space elevator as hanging down to the earth from geosynchronous orbit (the other half hangs up to balance the force). Since the elevator is hanging, it only needs to be lightly tethered to the earth, and might withstand earthquakes given a flexible tether. It will be straight. It must be tapered down in both directions from geosynchronous orbit for minimum tension at the root. No known material has the tensile strength to build one. But we can build variations such as the skyhooks suggested by Hans Moravec. These are basically rotating poles in orbit. An end comes down into the atmosphere, you grab on, and it yanks you up, and you let go at the top. You have to balance this with mass going down or some other energy input. An interesting variation on Earth-to-orbit systems appears in the article "The Launch Loop" by Keith Lofstrom in the December Analog magazine.