Dr. Travis S. Taylor heads up the cast of The Secret of Skinwalker Ranch and can be seen on The Machines that Built America on the History Channel. He has worked on various programs for the Department of Defense and NASA for the past twenty years. His expertise includes advanced propulsion concepts, very large space telescopes, space-based beamed-energy systems, future combat technologies, and next-generation space launch concepts. Taylor is also the author of pulse-pounding, cutting-edge science fiction novels, including the highly popular One Day on Mars, Tau Ceti Agenda, and the groundbreaking Warp Speed series. He is a regular on the History Channel's Life After People and The Universe series. Les Johnson is a physicist and the author of The Spacetime War; Mission to Methone; Rescue Mode (coauthored with Ben Bova); and Saving Proxima (coauthored with Travis S. Taylor). He is also the coeditor of the science/science fiction anthologies Going Interstellar and Stellaris: People of the Stars. He was technical consultant for the movies Europa Report and Lost in Space and has appeared in numerous documentaries on the Discovery and Science channels. Johnson was also the featured Interstellar Explorer in National Geographic Magazine and interviewed for Science Friday. By day, he serves as solar sail principal investigator of NASA's first interplanetary solar sail missions and leads research on various other advanced space propulsion technologies at the George C. Marshall Space Flight Center in Huntsville, Alabama.