Apollo 11: The Eagle Has Landed — an interactive Space Academy mission

Apollo 11 fulfilled President Kennedy's challenge to land a man on the Moon and return him safely before the decade's end. On July 16, 1969, Neil Armstrong, Michael Collins, and Buzz Aldrin lifted off from Launch Complex 39A atop a Saturn V whose first stage generated about 7.5 million pounds of thrust; after about one and a half Earth orbits, the third stage reignited to send them toward the Moon. In transit, Collins flew the command module Columbia through the transposition-and-docking maneuver — separating, rotating around, and extracting the lunar module Eagle from the spent rocket stage — without which there would be no lander at all. Four days later, on July 20, Armstrong and Aldrin undocked Eagle and began powered descent toward the Sea of Tranquility while Collins remained alone in orbit aboard Columbia.

During the descent, Eagle's guidance computer suddenly flashed a "1202" alarm — and then more alarms. In Mission Control, 26-year-old guidance officer Steve Bales, backed by computer expert Jack Garman, had seconds to decide. They recognized the alarms as executive overflows: the computer was overloaded (later traced to the rendezvous-radar switch position) but was correctly shedding low-priority tasks and still flying the landing. The call went up the chain — Garman to Bales to CAPCOM Charlie Duke — "We're GO on that alarm." Moments later, Armstrong looked through the window and saw the computer was steering them toward a crater strewn with large boulders. He took semi-automatic control and skimmed downrange, hunting for smooth ground as the fuel dwindled and Houston called out the seconds: "60 seconds"... "30 seconds."

Armstrong set Eagle down with only about 216 pounds of usable descent fuel remaining — later analysis put the reserve at roughly 45 to 50 seconds of flight — and radioed the words that ended eight years of national effort: "Houston, Tranquility Base here. The Eagle has landed." Touchdown came at 20:17:40 UTC on July 20, 1969. About six and a half hours later, at 02:56:15 UTC on July 21, Armstrong descended the ladder and pressed his boot into the ancient lunar dust before an audience estimated at some 600 million people, declaring, "That's one small step for [a] man, one giant leap for mankind." His very first surface task was a contingency soil sample, pocketed in case the crew had to lift off in a hurry. Aldrin soon joined him, and the famous image of Aldrin in his gold visor — with Armstrong and the Eagle reflected in it — captured humanity's first hours on another world. The plaque they left behind read, "We came in peace for all mankind."