Editing Apollo 11 (section)

=== Landing ===
[[File:AP11 FINAL APPROACH.ogv|thumb|Armstrong pilots ''Eagle'' to its landing on the Moon, July 20, 1969.]]
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 {{convert|300|ft|m|adj=mid|sp=us|-diameter}} crater (later determined to be [[West (lunar crater)|West crater]]), so he took semi-automatic control.{{sfn|Chaikin|1994|p=196}}{{sfn|Mindell|2008|pp=195–197}} Armstrong considered landing short of the boulder field so they could collect geological samples from it, but could not since their horizontal velocity was too high. Throughout the descent, Aldrin called out navigation data to Armstrong, who was busy piloting ''Eagle''. Now {{convert|107|ft|m|sp=us}} above the surface, Armstrong knew their propellant supply was dwindling and was determined to land at the first possible landing site.{{sfn|Chaikin|1994|p=197}}

Armstrong found a clear patch of ground and maneuvered the spacecraft towards it. As he got closer, now {{convert|250|ft|m|sp=us}} above the surface, he discovered his new landing site had a crater in it. He cleared the crater and found another patch of level ground. They were now {{convert|100|ft|m|sp=us}} from the surface, with only 90 seconds of propellant remaining. Lunar dust kicked up by the LM's engine began to impair his ability to determine the spacecraft's motion. Some large rocks jutted out of the dust cloud, and Armstrong focused on them during his descent so he could determine the spacecraft's speed.{{sfn|Chaikin|1994|pp=198–199}}

A light informed Aldrin that at least one of the {{convert|67|in|cm|0|adj=on}} probes hanging from ''Eagle''{{'s}} footpads had touched the surface a few moments before the landing and he said: "Contact light!" Armstrong was supposed to immediately shut the engine down, as the engineers suspected the pressure caused by the engine's own exhaust reflecting off the lunar surface could make it explode, but he forgot. Three seconds later, ''Eagle'' landed and Armstrong shut the engine down.{{sfn|Chaikin|1994|p=199}} Aldrin immediately said "Okay, engine stop. ACA—out of [[detent]]." Armstrong acknowledged: "Out of detent. Auto." Aldrin continued: "Mode control—both auto. Descent engine command override off. Engine arm—off. 413 is in."{{sfn|Mindell|2008|p=226}}
[[File:Apollo 11 Landing Site & West Crater.png|thumb|left|Landing site relative to [[West (lunar crater)|West crater]]]]
ACA was the [[Spacecraft attitude control|Attitude Control Assembly]]—the LM's control stick. Output went to the LGC to command the [[reaction control system]] (RCS) jets to fire. "Out of Detent" meant the stick had moved away from its centered position; it was spring-centered like the turn indicator in a car. Address 413 of the [[Apollo Abort Guidance System|Abort Guidance System]] (AGS) contained the variable that indicated the LM had landed.<ref name="ALSJ 1" />

''Eagle'' landed at 20:17:40 UTC on Sunday July 20 with {{convert|216|lb}} of usable fuel remaining. Information available to the crew and mission controllers during the landing showed the LM had enough fuel for another 25 seconds of powered flight before an abort without touchdown would have become unsafe,<ref name="ALSJ 1" />{{sfn|Orloff|2000|p=295}} but post-mission analysis showed that the real figure was probably closer to 50 seconds.<ref name="Horizons2013">{{cite journal |last1=Fjeld |first1=Paul |title=The Biggest Myth about the First Moon Landing |journal=Horizons |date=June 2013 |volume=38 |issue=6 |pages=5–6 |url=http://www.aiaahouston.org/wp-content/uploads/2013/07/Horizons_2013_05_and_06_low_resolution.pdf#page=5 |access-date=March 29, 2019 |archive-date=February 24, 2021 |archive-url=https://web.archive.org/web/20210224130506/http://www.aiaahouston.org/wp-content/uploads/2013/07/Horizons_2013_05_and_06_low_resolution.pdf#page=5 |url-status=live }}</ref> Apollo 11 landed with less fuel than most subsequent missions, and the astronauts encountered a premature low fuel warning. This was later found to be the result of the propellant [[Slosh dynamics|sloshing]] more than expected, uncovering a fuel sensor. On subsequent missions, extra anti-slosh baffles were added to the tanks to prevent this.<ref name="ALSJ 1" />

Armstrong acknowledged Aldrin's completion of the post-landing checklist with "Engine arm is off", before responding to the CAPCOM, Charles Duke, with the words, "Houston, [[Tranquility Base]] here. The ''[[Lunar Module Eagle|Eagle]]'' has landed." Armstrong's unrehearsed change of call sign from "Eagle" to "Tranquility Base" emphasized to listeners that landing was complete and successful.<ref>{{cite AV media |type=TV production |title=Failure is Not an Option |publisher=[[The History Channel]] |date=August 24, 2003 |oclc=54435670}}</ref> Duke expressed the relief at Mission Control: "Roger, Twan—Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot."<ref name="ALSJ 1">{{cite web |url=http://www.hq.nasa.gov/alsj/a11/a11.landing.html |title=The First Lunar Landing |date=1995 |editor-last=Jones |editor-first=Eric M. |work=Apollo 11 Lunar Surface Journal |publisher=NASA |access-date=June 13, 2013 |archive-date=December 27, 2016 |archive-url=https://web.archive.org/web/20161227230604/http://www.hq.nasa.gov/alsj/a11/a11.landing.html |url-status=live }}</ref><ref>{{cite web |url=https://www.bbc.co.uk/archive/james-may-speaks-to-charles-duke/zfnghbk |title=James May speaks to Charles Duke |date=2009 |publisher=BBC Archives |access-date=June 7, 2009 |archive-date=August 17, 2020 |archive-url=https://web.archive.org/web/20200817203306/https://www.bbc.co.uk/archive/james-may-speaks-to-charles-duke/zfnghbk |url-status=live }}</ref>
[[File:A New Look at the Apollo 11 Landing Site.ogg|thumb|[[Stereoscopy|3-D]] view from the [[Lunar Reconnaissance Orbiter]] (LRO) of Apollo 11 landing site]]

Two and a half hours after landing, before preparations began for the EVA, Aldrin radioed to Earth:
{{blockquote|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.<ref>{{cite web |url=http://www.hq.nasa.gov/alsj/a11/a11.postland.html |title=Post-landing Activities |date=1995 |editor-last=Jones |editor-first=Eric M. |work=Apollo 11 Lunar Surface Journal |publisher=NASA |access-date=June 13, 2013 |archive-date=May 10, 2013 |archive-url=https://web.archive.org/web/20130510224246/http://www.hq.nasa.gov/alsj/a11/a11.postland.html |url-status=live }}</ref>}}
He then took [[Eucharist|communion]] privately. At this time NASA was still fighting a lawsuit brought by atheist [[Madalyn Murray O'Hair]] (who had objected to the [[Apollo 8 Genesis reading|Apollo&nbsp;8 crew reading from the Book of Genesis]]) demanding that their astronauts refrain from broadcasting religious activities while in space. For this reason, Aldrin chose to refrain from directly mentioning taking communion on the Moon. Aldrin was an elder at the [[Webster, Texas|Webster]] [[Presbyterianism|Presbyterian Church]], and his communion kit was prepared by the pastor of the church, Dean Woodruff. Webster Presbyterian possesses the chalice used on the Moon and commemorates the event each year on the Sunday closest to July 20.{{sfn|Chaikin|1994|pp=204, 623}} The schedule for the mission called for the astronauts to follow the landing with a five-hour sleep period, but they chose to begin preparations for the EVA early, thinking they would be unable to sleep.{{sfn|Mission Evaluation Team|1969|pp=21–22}}