What's a "Space Elevator"?
What's so good about them?
"Space Elevator" problems
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A space elevator is basically a large lift going into Space. Of course, this isn't a very scientific definition of the term. That was just the very basic explanation.
The space elevator consists of several things:
The space elevator would draw its launch power from an electic power station on the ground. As it rides up the cable, less electrical energy is needed, because there is less gravitational force trying to pull it back down to Earth.
As well as the previously mentioned fact that electrical power from Earth could be used instead of on-board rocket fuel (which causes problems because you have to provide extra fuel to lift that fuel into space, and extra fuel to life that fuel into space...), there is another, possibly even more exciting, aspect.
This is the possibility of a free lunch. Let me explain: as well as using the elevator for sending stuff into space, we could use it as a runway back down to Earth (though not at the same time of course). The energy dissipated by the landing craft could be utilised, perhaps by using a dynamo or something, to generate electricity - which could then be used to power the next thing going up. This wouldn't save all the energy, courtesy of our old friends the Laws of Thermodynamics, but it would certainly save on electricity...
We need a cable that is long and strong enough to be able to stand being swung around by the Earth's gravitational forces. Then there's the tension with all the things going up and down it... you get the picture.
Fortunately, we are coming close to producing carbon nanotubes. A carbon nanotube, or CNT to its friends, is a material 100 times stronger than steel. CNT is pure carbon cylinders that were first created a decade ago by zapping graphite with lasers.
It has a tensile strength of 200 giga-pascals (GPa) when compared with graphite, quartz and alumna which have a GPa of just over 20. The minimum required tensile strength of a space tether would be 62 GPa, so we've got the material. Now all we need to do is build the thing...
Let's get this straight first. It is NOT a Sixties band or TV show. It's all the stuff that is flying around in orbit. And not TV satellites. Although they take up a lot of space, they do have their uses (or so Sky try to tell us). What isn't useful, is all the satellite screws, astronaut shoes and gloves, and bits of rocket that are up there right now doing... well... um... erm... absolutely nothing.
These things are flying around at high speeds. If something like a screw, or that astronaut's glove that's up there hits the space elevator, or the space tether, it could spell disaster. Unfortunately, there's nothing much we can do about all this so we've got to just hope for the best.