On May 25, 1961, President John F. Kennedy announced the goal of sending astronauts to the moon before the end of the decade. Coming just three weeks after Mercury astronaut Alan Shepard became the first American in space, Kennedy's bold challenge set the nation on a journey unlike any before in human history.

Eight years of hard work by thousands of Americans came to fruition on July 20, 1969, when Apollo 11 commander Neil Armstrong stepped out of the lunar module and took "one small step" in the Sea of Tranquility, calling it "a giant leap for mankind."

Innovation and even improvisation were necessary along the way. In December 1968, rather than letting lunar module delays slow the program, NASA changed plans to keep the momentum going. Apollo 8 would go all the way to the moon and orbit without a lunar module; it was the first manned flight of the massive Saturn V rocket.

Six of the missions -- Apollos 11, 12, 14, 15, 16 and 17 -- went on to land on the moon, studying soil mechanics, meteoroids, seismic, heat flow, lunar ranging, magnetic fields and solar wind. Apollos 7 and 9 tested spacecraft in Earth orbit; Apollo 10 orbited the moon as the dress rehearsal for the first landing. An oxygen tank explosion forced Apollo 13 to scrub its landing, but the "can-do" problem solving of the crew and mission control turned the mission into a "successful failure."

The program also drew inspiration from Apollo 1 astronauts Gus Grissom, Ed White and Roger Chaffee, who lost their lives in a fire during a launch pad test in 1967.