Interplanetary efficiency

The restricted three-body problem and efficient interplanetary space transit. As the article states, it costs a cool million to send a pound of fuel to the moon. This is a very hip and unintuitive way of zipping things around space with minimum fuel consumption. I clearly remember the first time I heard how Galileo used gravity assist (pdf) slingshoting around Venus, Earth, and Earth again before heaving out to Jupiter. Who would have thought that the most fuel efficient way to the outer solar system would be to head towards the sun? These "highways" are the next level of the same phenom. Pretty neat.