The Vision for Space Exploration (VSE) announced by President George W. Bush in 2004 sets NASA and the nation on a bold path to return to the Moon and one day put a human on Mars. The long-term endeavor represented by the VSE is, however, subject to the constraints imposed by annual funding. Given that the VSE may take tens of years to implement, a significant issue is whether NASA and the United States will have the workforce needed to achieve...