Solar sails use the sun's energy to fly spacecraft, or "flight by light." It sounds like something out of a science fiction novel. In fact, it is, first being mentioned in Jules Verne's From Earth to the Moon in 1865. It's been used as a way for characters to travel through space in many other books and movies, including Tron in 1985. Today, solar sails are a reality, and readers learn how their technology works as well as how successful trials with...