1950s: In 1957, the Russians launch Sputnik 1, the first space satellite, thus inaugurating the space age. This event prompts fears in the United States that the Soviet Union may be leading in military technology and may be able to launch ballistic missiles from Europe that could reach the United States. The Sputnik launch leads directly to the creation of the National Aeronautics and Space Administration (NASA) in 1958. The following decade is dominated by the so-called space race between the two superpowers.

Today: In 2004, President George W. Bush announces a new vision for the nation's space exploration program. The president commits the United States to a long-term human and robotic program to explore the solar system, starting with a return to the Moon that will ultimately enable future exploration of Mars and other destinations. The return to the Moon is planned for as early as 2015 and...