2 minutes. Link to Video
I wouldn’t want to be around when a piece of space junk cut through that cable and the bottom half fell back to Earth. Other than that, these things seem to have merit.
There’s a $4,000,000 dollar prize competition called Elevator 2010. They say we’ll need a cable with a tensile strength of 100 GPa to make this work. In theory carbon nanotubes can do that, but currently we’re only able to build cables in the 3-5 GPa range. They also claim the cable will be light and paper thin, so air friction would keep a falling cable from gaining enough speed to be a problem.
The cable would be 62,000 miles long. Satellites in geosynchronous orbit (stationary relative to Earth) are generally at 25,000 miles, but the extra length would make the end of that cable useful for slinging things to Mars or other distant destinations. Imagine swinging a ball on the end of a string.
The site also says the climbers would travel at 120 mph. That would be a 9 day journey to put something in geosynchronous orbit and a 22 day journey to the end of the cable. The system could carry one 15 ton payload per day and multiple climbers would be on the cable at once. They say this about getting them back down:
Multiple Space Elevators are possible, though there are some technical arguments against it. We believe this issue will end up being a political rather than a technocal one. In the initial years, there will be much more “up” traffic than “down” traffic, so even if there is only one Space Elevator, it will be possible to declare a “down” week every couple of month to accomodate such traffic.
It’s interesting to note that their spelling is worse than mine.
There’s another proposal called a space fountain where pellets are shot up from the Earth inside a tube. The kinetic energy of the pellets keeps the tube erect. However, if the stream of pellets were to stop due to power failure, mechanical failure, or sabotage the tube would come crashing to earth, making this one of the top four or five dumbest ideas I’ve ever heard. This proposal came from some very smart guys, and they did include redundant power supplies and redundant pellet guns. However, they were clearly smoking crack, and should not be taken seriously.
Update:
Also check out the LiftPort Group. They’ve got an informative forum and newsletter.
