For the past several years, the priorities of NASA have been governed by the Vision for Space Exploration. The Vision was announced by President Bush in January 2004 and endorsed by Congress in the 2005 and 2008 NASA authorisation acts. It directed NASA to focus its efforts on returning humans to the Moon by 2020 and some day sending them to Mars and "worlds beyond." The resulting efforts are now approaching major milestones, such as the end of the space shuttle program, design review decisions for the new spacecraft intended to replace the shuttle, and decisions about whether to extend the operation of the International Space Station. At the same time, concerns have grown about whether NASA can accomplish the planned program of human exploration of space without significant growth in its budget. This book explores the current U.S. space policy and its ramifications.