The Apollo 11 mission was the first manned mission to land on the Moon. It was the fifth human spaceflight of Project Apollo and the third human voyage to the Moon. Launched on July 16, 1969, it carried Mission Commander Neil Alden Armstrong, Command Module Pilot Michael Collins, and Lunar Module Pilot Edwin Eugene ‘Buzz’ Aldrin, Jr. On July 20, Armstrong and Aldrin became the first humans to walk on the Moon, while Collins orbited above.
The mission fulfilled President John F. Kennedy’s goal of reaching the moon by the end of the 1960s, which he expressed during a speech given before a joint session of Congress on May 25, 1961:
“I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth.”
A Saturn V launched Apollo 11 from the Kennedy Space Center on July 16, 1969 at 13:32 UTC (9:32 a.m. local time). It entered orbit 12 minutes later. After one and a half orbits, the S-IVB third-stage engine pushed the spacecraft onto its trajectory toward the Moon with the Trans Lunar Injection burn. About 30 minutes later the command/service module pair separated from this last remaining Saturn V stage and docked with the lunar module still nestled in the Lunar Module Adaptor. After the lunar module was extracted, the combined spacecraft headed for the Moon, while the third stage booster was directed toward the Sun.
On July 19 Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. In the thirty orbits that followed, the crew saw passing views of their landing site in the southern Sea of Tranquility (Mare Tranquillitatis) about 20 kilometers (12 mi) southwest of the crater Sabine D (0.67408N, 23.47297E). The landing site was selected in part because it had been characterized as relatively flat and smooth by the automated Ranger 8 and Surveyor 5 landers along with the Lunar Orbiter mapping spacecraft and unlikely to present major landing or extra-vehicular activity (EVA) challenges.
On July 20, 1969 the lunar module (LM) Eagle separated from the command module Columbia. Collins, alone aboard Columbia, inspected Eagle as it pirouetted before him to ensure the craft was not damaged.
As the descent began, Armstrong and Aldrin found that they were passing landmarks on the surface 4 seconds early and reported they were “long”. They would land miles west of their target point. The LM navigation and guidance computer distracted the crew with several unusual “1201″ and “1202″ program alarms. Inside Mission Control Center in Houston, Texas, computer engineer Jack Garman told guidance officer Steve Bales it was safe to continue the descent and this was relayed to the crew. When Armstrong again looked outside, he saw that the computer’s landing target was in a boulder-strewn area just north and east of a 400 meter diameter crater (later determined to be “West crater”, named for its location in the western part of the originally planned landing ellipse). Armstrong took semi-automatic control and with Aldrin calling out altitude and velocity data, landed at 20:17 UTC on July 20 with about 25 seconds of fuel left.
The program alarms were called executive overflows, during which the computer could not process all of its tasks in real time and had to postpone some of them. This was neither a computer error nor an astronaut error, but stemmed from a mistake in how the astronauts had been trained. Although unneeded for the landing, the rendezvous radar was intentionally turned on to make ready for a fast abort. Ground simulation setups had not foreseen that a fast stream of spurious interrupts from this radar could happen, depending upon how the hardware randomly powered up before the LM then began nearing the lunar surface: Hence the computer had to deal with data from two radars, not the landing radar alone, which led to the overload.
Although Apollo 11 landed with less fuel than other missions, they also encountered a premature low fuel warning. It was later found to be caused by the lunar gravity permitting greater propellant ’slosh’ which had uncovered a fuel sensor. On future missions extra baffles were added to the tanks.
Buzz Aldrin spoke the first words (albeit technical jargon) from the LM on the lunar surface. Throughout the descent Aldrin had called out navigation data to Armstrong, who was busy piloting the LM. As Eagle landed Aldrin said, “Contact light! Okay, engine stop. ACA – out of detent.” Armstrong acknowledged “Out of detent” and Aldrin continued, “Mode control – both auto. Descent engine command override off. Engine arm – off. 413 is in.”
Then Armstrong said the famous words, “Houston, Tranquility Base here. The Eagle has landed.” Armstrong’s abrupt change of call sign from “Eagle” to “Tranquility Base” caused momentary confusion at Mission Control. Charles Duke, acting as CAPCOM during the landing phase, acknowledged their landing, expressing the relief of a Mission Control made nervous by a long landing that almost expended all of the lunar module Eagle’s fuel. Duke’s famous first words to the Apollo 11 crew on the surface of the moon were flustered “Roger, Twank…Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue here. We’re breathing again. Thanks a lot!” expressing the relief of Mission Control after the unexpectedly drawn-out descent.
Shortly after landing, before preparations began for the EVA, Aldrin broadcast this:
This is the LM pilot. I’d like to take this opportunity to ask every person listening in, whoever and wherever they may be, to pause for a moment and contemplate the events of the past few hours and to give thanks in his or her own way.
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