Apollo 11 Lunar Module Eagle lands on Moon; Neil Armstrong becomes first human to step on surface

Launched on July 16, 1969, Apollo 11 represented the culmination of NASA's decade-long effort initiated by President John F. Kennedy in 1961 to land a human on the Moon. On July 20, astronauts Neil Armstrong and Edwin "Buzz" Aldrin separated the Lunar Module Eagle from the Command Module Columbia, piloted by Michael Collins in lunar orbit. As Eagle descended toward Mare Tranquillitatis (the Sea of Tranquility), the spacecraft's primary guidance computer triggered unexpected 1201 and 1202 program alarms caused by executive overflow from the rendezvous radar system.

Guided by Mission Control flight controllers in Houston, Armstrong took manual attitude control when he realized the automated trajectory was steering Eagle into a boulder-strewn crater field surrounding West Crater. Steering the spacecraft downrange while carefully managing dwindling propellants, Armstrong landed Eagle safely on the lunar surface at 20:17 UTC with less than thirty seconds of descent fuel remaining. Moments after touchdown, Armstrong radioed back to Mission Control: "Houston, Tranquility Base here. The Eagle has landed."

At 02:56 UTC on July 21 (late evening July 20 in North America), Armstrong descended Eagle's ladder, opened the Modular Equipment Transporter, and stepped onto the lunar surface, uttering the iconic phrase: "That's one small step for man, one giant leap for mankind." Joined minutes later by Aldrin, the pair spent over two hours conducting an extravehicular activity (EVA). They collected 21.5 kilograms of lunar rock and regolith samples, deployed the Passive Seismic Experiment Package and a Laser Ranging Retroreflector, and erected the flag of the United States. The successful landing fulfilled a major national goal and marked a profound milestone in human technological civilization.