Talking about building an interstellar space ship makes you sound like a sci-fi fan who’s lost touch with the real world. Unless you’re Mae Jemison, a former astronaut and the head of 100 Year Starship, an organization the home page of which boldly commands, “Let’s make human interstellar travel capabilities a reality within the next hundred years.” The problem: space is big, and our current rocket technology isn’t cutting it, says Marc Millis, the head of the Tau Zero Foundation. The heads of yet another interstellar organization, Starship Century, think they are on the right track. The technology is the beam sail, pushed with microwave beams, instead of wind, to extremely high speeds.