Book excerpt: Louis Friedman, Executive Director of the Planetary Society, presents the first comprehensive look at the science and history behind solar sailing and other designs for space travel. Serious science readers and space buffs alike will be fascinated by designs for the square sail, disk sail, and the heliogyro (which features flexible sails many kilometers long). Friedman compares solar sailing to other proposed propulsion sytems such as ion drives and laser propulsion, and takes an insider's look at the million-dollar JPL project of the late '70s, which was the first attempt at a working model. Illustrated.