Delftsman

Apollo 11

Left to right: Armstrong, Collins, Aldrin

40 years ago today, man embarked on the greatest adventure he had ever undertaken. Three brave men, Neil Armstrong, Michael Collins, and Edwin E. Aldrin, Jr. rode atop the mighty Saturn 5 rocket on their way to land on the moon. The rocket was launched 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.

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).

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.

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

Aldrin unpacks experiments from the LEM, named Eagle.

Posted by Delftsman3 at July 16, 2009 01:57 PM | TrackBack