In his 14 January 2004 speech on the future of space exploration, U.S. President George W. Bush proposed a return to the Moon followed by human missions to Mars and to worlds beyond. Bush's proposal called for robotic missions and new manned space vehicles to replace an aging set of space shuttles, and sought a new justification for space exploration. In the words of former NASA Administrator Sean O'Keefe, in The Vision for Space Exploration, this plan is not merely for the sake of adventure, however exciting that might be, but seeks answers to profound scientific and philosophic questions. Bush's proposal stimulated renewed reflection on the goals of our nation's space policy and on the means (financial and otherwise) for achieving these goals. A return to such first-order questioning of our goals for space has been long overdue. The Columbia Accident Investigation Board, which was convened by NASA in 2003 following the shuttle disaster, described a lack, over the past three decades, of any national mandate providing NASA a compelling mission requiring human presence in space <Keiper, 2003>.