Launch and lunar orbit injection

Thousands of spectators camped out to watch the launch of Apollo 11 adjacent to the Kennedy Space Center. The Saturn V carrying Apollo 11 took several seconds to clear the tower on July 16, 1969. A condensation cloud forms around an interstage as the Saturn V approached Mach 1, one minute into the flight. Engineers working in the launch control center. The Eagle in lunar orbit immediately after separating from Columbia.

In addition to throngs of people crowding highways and beaches near the launch site, millions watched the event on television, with NASA Chief of Public Information Jack King providing commentary. President Richard Nixon viewed the proceedings from the Oval Office of the White House.

A Saturn V launched Apollo 11 from Launch Pad 39A, part of the Launch Complex 39 site at the Kennedy Space Center on July 16, 1969 at 13:32:00 UTC (9:32:00 a.m. local time). It entered orbit 12 minutes later.[1] 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 at 16:22:13 UTC. 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 flew on a trajectory past the moon and into solar orbit.[6]

On July 19 at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. In the thirty orbits[7] 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.[8]

Lunar descent

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 that they were "long": they would land miles west of their target point.

Five minutes into the descent burn, and 6000 feet above the surface of the moon, the LM navigation and guidance computer distracted the crew with the first of several unexpected "1202" and "1201" 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. The program alarms indicated "executive overflows", where the guidance computer could not complete all of its tasks in real time and had to postpone some of them.[9] 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.[10][11][12]

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 300 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[13] and, with Aldrin calling out altitude and velocity data, landed at 20:17 UTC on July 20 with about 25 seconds of fuel left.[14]

Apollo 11 landed with less fuel than other missions, and the astronauts also encountered a premature low fuel warning. This was later found to have been due to greater propellant 'slosh' than expected uncovering a fuel sensor. On subsequent missions, extra baffles were added to the tanks to prevent this.[14]

Throughout the descent Aldrin had called out navigation data to Armstrong, who was busy piloting the LM. A few moments before the landing, a light informed Aldrin that at least one of the 67-inch probes hanging from Eagle's footpads had touched the surface, and he said "Contact light!". Three seconds later, Eagle landed and Armstrong said "Shutdown". Aldrin immediately said "Okay, engine stop. ACA - out of detent." Armstrong acknowledged "Out of detent. Auto" and Aldrin continued "Mode control - both auto. Descent engine command override off. Engine arm - off. 413 is in."

Charles Duke, acting as CAPCOM during the landing phase, acknowledged their landing by saying "We copy you down, Eagle".

Armstrong continued with the remainder of the post landing checklist, "Engine arm is off." before responding to Duke with 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 and Duke remained silent for a couple of seconds before replying: "Roger, Twank...Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot!" expressing the relief of Mission Control after the unexpectedly drawn-out descent.[14][15]

Two and a half hours after landing, before preparations began for the EVA, Aldrin broadcast that:

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.[16]
 
 
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