NASA is again reorganizing its resources to accomplish its fluctuating missions. The fourth edition of Introduction to Space: The Science of Spaceflight has received a major overhaul to bring to you a readable understanding of how these goals may be achieved. It has been updated with the latest information on the science and technology involved to explain why astronauts are weightless, what satellites do and why they don t fall from the sky, how we will live on Mars, and whether or not there is life elsewhere in the universe. The book is now profusely illustrated throughout with 274 illustrations of which 102 are in color. All measurements are presented in both common units and in the international System of Units (SI), commonly called metric units.