[Don Joe]

In other words, nothing we can currently build is strong enough.

Nothing can be strong enough, period.

It's like trying to bring the Moon close to the Earth. You can't. It'll break up due to the Roche Limit. You can't break the laws of nature.

The tidal force will destroy a space elevator -- even if you can erect it -- as soon as you try to use it.

[Josh in PA]

If the tidal force doesn't destroy it, then a few space rocks definently will.

[Rifleman]

The Roche Limit doesn't apply.

For those that don't study celestial mechanics the Roche Limit is just the closest orbit that a given body can occupy without the difference in the orbital speed of the inner most and outermost points of the body overcoming that body's gravitation. It assumes zero mechanical strength which is decidedly not the case for a structure like a skyhook.

The models for this kind of artifact are well understood. It is basically a spinning length of tapered cable. Engineers understand things like mechanics of materials, celestial mechanics, electrical and gravitational forces, etc. Given a strong enough material and Bucky tubes are in the ball park, the thing is buildable. The numbers are big and expensive, but so what. The payoff is huge, ie kilobux/tonne to orbit rather than megabux/tonne. Also note that a skyhook can deliver huge amounts of delta v to a payload. Mars, the Asteroids and Jupiter's moons anyone?

Fifteen years is probably a very optimistic number, but if we don't kill ourselves or descend into barbarism, men will build these things. And soon.