A Space Elevator?!

Picture if you will...

Picture driving by a sprawling meadow. As you look out of the window, a black vertical hair seems to be hanging in front of your eye and it catches your attention. But then you notice that it is fixed in space... It's a thin black line, almost like the trace of a film-scratch on a picture. Seeing that it's practically right in front of you, you get out for a closer look.

Incredibly, it turns out that the line was only 20 meters away when you spotted it -- a black tether only a quarter-inch in diameter and anchored to the ground. The tether reaches straight up and quickly disappears from view into the clear blue sky. You tug down on the tether, and sure enough there is something holding it up, though there's no balloon, helicopter or tall structure within miles.

To understand what's going on, imagine zooming out until the meadow, nearby cities and finally the entire planet appears the size of coin. The tether spans almost eight times the diameter of the planet, points directly outwards, and is strapped to a steel ball. As the planet rotates, it carries with it the tether and ball, like a super-long spinning yo-yo; as the ball tries to escape, it keeps the tether taut.

Welcome to the space elevator: a stationary tether rotating with the Earth, held up by a weight at its end, and serving as a track on which electric vehicles called "climbers" can travel up and down carrying about 10 tons of payload. The technical details, of course, are much more involved than this.

The Space Elevator is a space transportation system that is a radical departure from rocket-based space travel. Contrary to our first intuition, it is actually possible to construct a physical "railroad to space", such that leaving the planet will involve riding out rather than rocketing out.

Building this railroad system takes two steps - laying the track, and running the trains.

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