President Bush’s new vision for space exploration starts with robotic missions and culminates with a manned Moon landing that will lay the groundwork for an eventual trip to Mars. Critics, however, have noted a troubling gap in the timeline: The space shuttle will be phased out in 2010, but the new Crew Exploration Vehicle won’t make its first manned flight until 2014. That means that for four years Americans won’t have a ride to space.

A series of robotic “trailblazer” missions to the Moon get under way. Around this time, NASA conducts the first flight test of the Crew Exploration Vehicle–at this early stage, unmanned.

After nearly three decades of service, the nation’s aging space shuttle fleet is retired. In the past six years, the three remaining shuttles have flown 25 to 30 missions to finish the assembly of the International Space Station.

Six years after the first unmanned test, NASA launches its first manned mission in the new Crew Exploration Vehicle, possibly a visit to the now completed International Space Station.

NASA conducts the first “extended” human expedition to the lunar surface. (Apollo astronauts stayed no more than three days on the Moon, whereas this mission could last as long as two weeks.) Earlier robotic missions have prepared the landing site for the astronauts’ arrival.

NASA completes its research aboard the International Space Station. The research, in line with President Bush’s mandate, focused on learning how to keep astronauts safe and healthy during long journeys into space.

NASA undertakes the first human mission beyond the Moon–potentially a circumnavigation of Mars, a visit to a near-Earth asteroid, or the construction of a deep-space telescope.