Lunar Space Elevator

A few weeks ago, slashdot covered this article on the idea of a lunar space elevator.

A space elevator is typically thought of as a long cable that hangs down from space that provides a very energy efficient way to transport materials from the ground into space. On Earth, it would work by putting a spool of cable in geosynchronous orbit, and then slowly lowering the cable down to Earth while extending a counter weight away from the Earth.

Geosynchronous orbit is an orbit that takes 24 hours to make it all of the way around. This type of orbit will keep a satellite exactly above the same point on Earth. This is a very common orbit for satellites. For example, TV satellites are kept in this type of orbit.

The problem is that to stay balanced like this, the center of gravity of an Earth-based space elevator would have to be 22,236 miles above the surface. That would mean you’d need almost as much cable as what it would take to reach all of the way around the Earth (24,859 miles). That’s a lot of cable, so we’d need to to be lighter and stronger that any materials we currently have available (carbon nanotubes look promising though).

This is where the Moon comes in. The force of gravity on the Moon is only 1/6 that of gravity on Earth. We couldn’t really put a space elevator in geosynchronous orbit over the Moon because the Moon rotates so slowly, but we could balance a lunar space elevator at a Lagrangian point. This would be a great way to test out the space elevator idea, and even get some use out of it by providing a cheap way to get stuff off of the surface of the Moon. I think NASA should seriously keep this in mind if we’re ever going to build a permanent lunar base.