I wish to acknowledge the contributions of my colleagues at Pioneer Astronautics—Mark Berggren, Stacy Carrera, Heather Rose, Jonathan Rasmussen, Max Shub, Jacob Romero, Steven Fatur, Andrew Miller, and Carie Fay—who are helping to develop many of the technologies discussed in this book. I also wish to acknowledge the help of my friends Richard Heidmann, Etienne Martinache, Richard Wagner, Freeman Dyson, and Mitchell Burnside Clapp, who reviewed early drafts of the manuscript or parts thereof and made many useful comments. Thanks are also due to Nicole Sommer-Lecht and Steven L. Mitchell of Prometheus Books for their excellent contributions with the book's art and editorial work, respectively. Special thanks are also due to my intrepid agent, Laurie Fox, who found an excellent publisher for the book. Most thanks of all must be given to my clever, funny, and darling wife, Hope Ann Zubrin, without whose patience, love, and constant support this book never could have been written.