We will build new ships to carry man forward into the universe, to gain a new foothold on the moon, and to prepare for new journeys to worlds beyond our own.

—President George W. Bush, January 14, 2004

How will a country at war and in deficit pay for such things?

—Harvard Independent Newsmagazine, February 12, 2004

Humans seem to have an inherent desire to surmount great obstacles and push into new frontiers. There have always been brave people willing to risk their lives on bold and dangerous journeys into uncharted territory. They have climbed Mount Everest, traversed wild jungles, crossed barren deserts, and sailed stormy seas. Successful explorers become popular heroes. Their achievements thrill and delight people who do not have the energy, resources, or courage to go themselves.

America's space program taps into this spirit of adventure. Astronauts became the heroic explorers...