I wrote this book because I wanted to learn more about interstel- lar flight. Not the Star Trek notion of tearing around the Galaxy in a huge spaceship-that was obviously beyond existing tech- nology-but a more realistic mission. In 1989 I had videotaped Voyager 2's encounter with Neptune and watched the drama of robotic exploration over and over again. I started to wonder whether we could do something similar with Alpha Centauri, the nearest star...