Apollo 11 was the spaceflight that landed the first humans on the Moon, Americans Neil Armstrong and Buzz Aldrin, on July 20, 1969, at 20:18 UTC. Armstrong became the first to step onto the lunar surface six hours later on July 21 at 02:56 UTC.

Who was the man to walk on the moon?

Apollo 11 (July 16–24, 1969) was the American spaceflight that first landed humans on the Moon.

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Apollo 11 (July 16–24, 1969) was the American <a href="https://en.m.wikipedia.org/wiki/Human_spaceflight">spaceflight </a>that first <a href="https://en.m.wikipedia.org/wiki/Moon_landing">landed </a>humans on the <a href="https://en.m.wikipedia.org/wiki/Moon">Moon </a>. Commander <a href="https://en.m.wikipedia.org/wiki/Neil_Armstrong">Neil Armstrong </a>and lunar module pilot <a href="https://en.m.wikipedia.org/wiki/Buzz_Aldrin">Buzz Aldrin </a>landed the <a href="https://en.m.wikipedia.org/wiki/Apollo_Lunar_Module">Apollo Lunar Module </a><a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">Eagle </a>on July 20, 1969, at 20:17 <a href="https://en.m.wikipedia.org/wiki/Coordinated_Universal_Time">UTC </a>, and Armstrong became the first person to step onto the Moon's surface six hours and 39 minutes later, on July 21 at 02:56 UTC. Aldrin joined him 19 minutes later, and they spent about two and a quarter hours together exploring the site they had named <a href="https://en.m.wikipedia.org/wiki/Tranquility_Base">Tranquility Base </a>upon landing. Armstrong and Aldrin collected 47.5 pounds (21.5 kg) of lunar material to bring back to Earth as pilot <a href="https://en.m.wikipedia.org/wiki/Michael_Collins_(astronaut)">Michael Collins </a>flew the <a href="https://en.m.wikipedia.org/wiki/Command_Module_Columbia">Command Module Columbia </a>in <a href="https://en.m.wikipedia.org/wiki/Lunar_orbit">lunar orbit </a>, and were on the Moon's surface for 21 hours, 36 minutes before lifting off to rejoin Columbia .

<ul><li><a href="https://en.m.wikipedia.org/wiki/Apollo_command_and_service_module">Apollo CSM </a>-107 </li><li><a href="https://en.m.wikipedia.org/wiki/Apollo_Lunar_Module">Apollo LM </a>-5 </li> </ul>

<ul><li>CSM: <a class="mw-redirect" href="https://en.m.wikipedia.org/wiki/North_American_Rockwell">North American Rockwell </a> </li><li>LM: <a href="https://en.m.wikipedia.org/wiki/Grumman">Grumman </a> </li> </ul>

<ul><li><a href="https://en.m.wikipedia.org/wiki/Neil_Armstrong">Neil A. Armstrong </a> </li><li><a href="https://en.m.wikipedia.org/wiki/Michael_Collins_(astronaut)">Michael Collins </a> </li><li><a href="https://en.m.wikipedia.org/wiki/Buzz_Aldrin">Edwin E. Aldrin Jr. </a> </li> </ul>

<ul><li>CSM: <a class="mw-redirect" href="https://en.m.wikipedia.org/wiki/Command_Module_Columbia">Columbia </a> </li><li>LM: <a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">Eagle </a> </li><li>On surface: <a href="https://en.m.wikipedia.org/wiki/Tranquility_Base">Tranquility Base </a> </li> </ul>

<ul><li>North Pacific Ocean </li><li><a class="external text" href="https://geohack.toolforge.org/geohack.php?pagename=Apollo_11&params=13_19_N_169_9_W_type:event&title=Apollo+11+splashdown">13°19′N 169°9′W </a> </li> </ul>

<ul><li><a href="https://en.m.wikipedia.org/wiki/Tranquility_Base">Tranquility Base </a>, </li><li><a href="https://en.m.wikipedia.org/wiki/Mare_Tranquillitatis">Mare Tranquillitatis </a> </li><li><a class="external text" href="https://geohack.toolforge.org/geohack.php?pagename=Apollo_11&params=0.67416_N_23.47314_E_globe:moon">0.67416°N 23.47314°E </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-11">[11] </a> </li> </ul>

Apollo 11 was launched by a <a href="https://en.m.wikipedia.org/wiki/Saturn_V">Saturn V </a>rocket from <a href="https://en.m.wikipedia.org/wiki/Kennedy_Space_Center">Kennedy Space Center </a>on <a href="https://en.m.wikipedia.org/wiki/Merritt_Island,_Florida">Merritt Island, Florida </a>, on July 16 at 13:32 UTC, and it was the fifth crewed mission of <a href="https://en.m.wikipedia.org/wiki/NASA">NASA </a>'s <a href="https://en.m.wikipedia.org/wiki/Apollo_program">Apollo program </a>. The Apollo <a href="https://en.m.wikipedia.org/wiki/Apollo_(spacecraft)">spacecraft </a>had three parts: a <a href="https://en.m.wikipedia.org/wiki/Apollo_command_and_service_module#Command_module_(CM)">command module (CM) </a>with a cabin for the three astronauts, the only part that returned to Earth; a <a href="https://en.m.wikipedia.org/wiki/Apollo_service_module">service module (SM) </a>, which supported the command module with propulsion, electrical power, oxygen, and water; and a <a href="https://en.m.wikipedia.org/wiki/Apollo_Lunar_Module">lunar module (LM) </a>that had two stages—a descent stage for landing on the Moon and an ascent stage to place the astronauts back into lunar orbit.

After being <a href="https://en.m.wikipedia.org/wiki/Trans-lunar_injection">sent to the Moon </a>by the Saturn V's third stage, the astronauts separated the spacecraft from it and traveled for three days until they entered lunar orbit. Armstrong and Aldrin then moved into <a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">Eagle </a>and landed in the <a href="https://en.m.wikipedia.org/wiki/Sea_of_Tranquility">Sea of Tranquility </a>on July 20. The astronauts used Eagle ' s ascent stage to lift off from the lunar surface and rejoin Collins in the command module. They jettisoned Eagle before they performed the maneuvers that propelled Columbia out of the last of its 30 lunar orbits onto a trajectory back to Earth.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000109-8">[8] </a> They returned to Earth and <a href="https://en.m.wikipedia.org/wiki/Splashdown">splashed down </a>in the Pacific Ocean on July 24 after more than eight days in space.

Armstrong's first step onto the lunar surface was broadcast on <a href="https://en.m.wikipedia.org/wiki/Live_television">live TV </a>to a worldwide audience. He described the event as "one small step for [a] man, one giant leap for mankind."<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-transcript-14">[a] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-ALSJ_4-15">[14] </a> Apollo 11 effectively proved US victory in the <a href="https://en.m.wikipedia.org/wiki/Space_Race">Space Race </a>to demonstrate spaceflight superiority, by fulfilling a national goal proposed in 1961 by <a href="https://en.m.wikipedia.org/wiki/President_of_the_United_States">President </a><a href="https://en.m.wikipedia.org/wiki/John_F._Kennedy">John F. Kennedy </a>, "before this decade is out, of landing a man on the Moon and returning him safely to the Earth."<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-16">[15] </a>

In the late <a href="https://en.m.wikipedia.org/wiki/1950s">1950s </a>and early <a href="https://en.m.wikipedia.org/wiki/1960s">1960s </a>, the United States was engaged in the <a href="https://en.m.wikipedia.org/wiki/Cold_War">Cold War </a>, a geopolitical rivalry with the <a href="https://en.m.wikipedia.org/wiki/Soviet_Union">Soviet Union </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTELogsdon1976134-17">[16] </a> On October 4, 1957, the Soviet Union launched <a href="https://en.m.wikipedia.org/wiki/Sputnik_1">Sputnik 1 </a>, the first <a href="https://en.m.wikipedia.org/wiki/Satellite">artificial satellite </a>. This surprise success fired fears and imaginations around the world. It demonstrated that the Soviet Union had the capability to deliver nuclear weapons over intercontinental distances, and challenged American claims of military, economic and technological superiority.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTELogsdon197613%E2%80%9315-18">[17] </a> This precipitated the <a href="https://en.m.wikipedia.org/wiki/Sputnik_crisis">Sputnik crisis </a>, and triggered the <a href="https://en.m.wikipedia.org/wiki/Space_Race">Space Race </a>to prove which superpower would achieve superior spaceflight capability.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson19791-19">[18] </a> <a href="https://en.m.wikipedia.org/wiki/President_of_the_United_States">President </a><a href="https://en.m.wikipedia.org/wiki/Dwight_D._Eisenhower">Dwight D. Eisenhower </a>responded to the Sputnik challenge by creating the <a href="https://en.m.wikipedia.org/wiki/National_Aeronautics_and_Space_Administration">National Aeronautics and Space Administration </a>(NASA), and initiating <a href="https://en.m.wikipedia.org/wiki/Project_Mercury">Project Mercury </a>,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESwensonGrimwoodAlexander1966101%E2%80%93106-20">[19] </a> which aimed to launch a man into <a href="https://en.m.wikipedia.org/wiki/Earth_orbit">Earth orbit </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESwensonGrimwoodAlexander1966134-21">[20] </a> But on April 12, 1961, Soviet <a href="https://en.m.wikipedia.org/wiki/Cosmonaut">cosmonaut </a><a href="https://en.m.wikipedia.org/wiki/Yuri_Gagarin">Yuri Gagarin </a>became the first person in space, and the first to orbit the Earth.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESwensonGrimwoodAlexander1966332%E2%80%93333-22">[21] </a> Nearly a month later, on May 5, 1961, <a href="https://en.m.wikipedia.org/wiki/Alan_Shepard">Alan Shepard </a>became the first American in space, completing a 15-minute suborbital journey. After being recovered from the Atlantic Ocean, he received a congratulatory telephone call from Eisenhower's successor, <a href="https://en.m.wikipedia.org/wiki/John_F._Kennedy">John F. Kennedy </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTELogsdon1976121-23">[22] </a>

Since the <a href="https://en.m.wikipedia.org/wiki/Soviet_Union">Soviet Union </a>had higher lift capacity <a href="https://en.m.wikipedia.org/wiki/Launch_vehicle">launch vehicles </a>, Kennedy chose, from among options presented by NASA, a challenge beyond the capacity of the existing generation of rocketry, so that the US and Soviet Union would be starting from a position of equality. A crewed mission to the Moon would serve this purpose.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTELogsdon1976112%E2%80%93117-24">[23] </a>

On May 25, 1961, Kennedy addressed the <a href="https://en.m.wikipedia.org/wiki/United_States_Congress">United States Congress </a>on "Urgent National Needs" and declared:

I believe that this nation should commit itself to achieving the goal, before this decade [1960s] is out, of landing a man on the Moon and returning him safely to the Earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish. We propose to accelerate the development of the appropriate lunar space craft. We propose to develop alternate liquid and solid fuel boosters, much larger than any now being developed, until certain which is superior. We propose additional funds for other engine development and for unmanned explorations—explorations which are particularly important for one purpose which this nation will never overlook: the survival of the man who first makes this daring flight. But in a very real sense, it will not be one man going to the Moon—if we make this judgment affirmatively, it will be an entire nation. For all of us must work to put him there.

On September 12, 1962, Kennedy <a href="https://en.m.wikipedia.org/wiki/We_choose_to_go_to_the_Moon">delivered another speech </a>before a crowd of about 40,000 people in the <a href="https://en.m.wikipedia.org/wiki/Rice_Stadium_(Rice_University)">Rice University football stadium </a>in <a href="https://en.m.wikipedia.org/wiki/Houston">Houston </a>, <a href="https://en.m.wikipedia.org/wiki/Texas">Texas </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-26">[25] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-27">[26] </a> A widely quoted refrain from the middle portion of the speech reads as follows:

There is no strife, no prejudice, no national conflict in outer space as yet. Its hazards are hostile to us all. Its conquest deserves the best of all mankind, and its opportunity for peaceful cooperation may never come again. But why, some say, the Moon? Why choose this as our goal? And they may well ask, why climb the highest mountain? Why, 35 years ago, <a href="https://en.m.wikipedia.org/wiki/Spirit_of_St._Louis">fly the Atlantic </a>? Why does <a href="https://en.m.wikipedia.org/wiki/Rice%E2%80%93Texas_football_rivalry">Rice play Texas </a>? We choose to go to the Moon! We choose to go to the Moon  ... We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one we intend to win, and the others, too.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-28">[27] </a>

In spite of that, the proposed program faced the opposition of many Americans and was dubbed a "<a href="https://en.m.wikipedia.org/wiki/Boondoggle">moondoggle </a>" by <a href="https://en.m.wikipedia.org/wiki/Norbert_Wiener">Norbert Wiener </a>, a mathematician at the <a href="https://en.m.wikipedia.org/wiki/Massachusetts_Institute_of_Technology">Massachusetts Institute of Technology </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-29">[28] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-30">[29] </a> The effort to land a man on the Moon already had a name: <a href="https://en.m.wikipedia.org/wiki/Project_Apollo">Project Apollo </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson197915-31">[30] </a> When Kennedy met with <a href="https://en.m.wikipedia.org/wiki/Nikita_Khrushchev">Nikita Khrushchev </a>, the <a href="https://en.m.wikipedia.org/wiki/Premier_of_the_Soviet_Union">Premier of the Soviet Union </a>in June 1961, he proposed making the Moon landing a joint project, but Khrushchev did not take up the offer.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTELogsdon201132-32">[31] </a> Kennedy again proposed a joint expedition to the Moon in a speech to the <a href="https://en.m.wikipedia.org/wiki/United_Nations_General_Assembly">United Nations General Assembly </a>on September 20, 1963.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-33">[32] </a> The idea of a joint Moon mission was abandoned after Kennedy's death.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-34">[33] </a>

An early and crucial decision was choosing <a href="https://en.m.wikipedia.org/wiki/Lunar_orbit_rendezvous">lunar orbit rendezvous </a>over both <a href="https://en.m.wikipedia.org/wiki/Direct_ascent">direct ascent </a>and <a href="https://en.m.wikipedia.org/wiki/Earth_orbit_rendezvous">Earth orbit rendezvous </a>. A <a href="https://en.m.wikipedia.org/wiki/Space_rendezvous">space rendezvous </a>is an <a href="https://en.m.wikipedia.org/wiki/Orbital_maneuver">orbital maneuver </a>in which two spacecraft navigate through space and meet up. In July 1962 NASA head <a href="https://en.m.wikipedia.org/wiki/James_E._Webb">James Webb </a>announced that lunar orbit rendezvous would be used<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-35">[34] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESwensonGrimwoodAlexander196685%E2%80%9386-36">[35] </a> and that the <a href="https://en.m.wikipedia.org/wiki/Apollo_(spacecraft)">Apollo spacecraft </a>would have three major parts: a command module (CM) with a cabin for the three astronauts, and the only part that returned to Earth; a service module (SM), which supported the command module with propulsion, electrical power, oxygen, and water; and a lunar module (LM) that had two stages—a descent stage for landing on the Moon, and an ascent stage to place the astronauts back into lunar orbit.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson197972%E2%80%9377-37">[36] </a> This design meant the spacecraft could be launched by a single <a href="https://en.m.wikipedia.org/wiki/Saturn_V">Saturn V </a>rocket that was then under development.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson197948%E2%80%9349-38">[37] </a>

Technologies and techniques required for Apollo were developed by <a href="https://en.m.wikipedia.org/wiki/Project_Gemini">Project Gemini </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979181%E2%80%93182,_205%E2%80%93208-39">[38] </a> The Apollo project was enabled by NASA's adoption of new advances in <a href="https://en.m.wikipedia.org/wiki/Semiconductor">semiconductor </a><a href="https://en.m.wikipedia.org/wiki/Electronic_technology">electronic technology </a>, including <a href="https://en.m.wikipedia.org/wiki/Metal-oxide-semiconductor_field-effect_transistor">metal-oxide-semiconductor field-effect transistors </a>(MOSFETs) in the <a href="https://en.m.wikipedia.org/wiki/Interplanetary_Monitoring_Platform">Interplanetary Monitoring Platform </a>(IMP)<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-40">[39] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-41">[40] </a> and <a href="https://en.m.wikipedia.org/wiki/Silicon">silicon </a><a href="https://en.m.wikipedia.org/wiki/Integrated_circuit">integrated circuit </a>(IC) chips in the <a href="https://en.m.wikipedia.org/wiki/Apollo_Guidance_Computer">Apollo Guidance Computer </a>(AGC).<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-42">[41] </a>

Project Apollo was abruptly halted by the <a href="https://en.m.wikipedia.org/wiki/Apollo_1">Apollo 1 </a>fire on January 27, 1967, in which astronauts <a href="https://en.m.wikipedia.org/wiki/Gus_Grissom">Gus Grissom </a>, <a href="https://en.m.wikipedia.org/wiki/Ed_White_(astronaut)">Ed White </a>, and <a href="https://en.m.wikipedia.org/wiki/Roger_B._Chaffee">Roger B. Chaffee </a>died, and the subsequent investigation.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979214%E2%80%93218-43">[42] </a> In October 1968, <a href="https://en.m.wikipedia.org/wiki/Apollo_7">Apollo 7 </a>evaluated the command module in Earth orbit,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979265%E2%80%93272-44">[43] </a> and in December <a href="https://en.m.wikipedia.org/wiki/Apollo_8">Apollo 8 </a>tested it in lunar orbit.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979274%E2%80%93284-45">[44] </a> In March 1969, <a href="https://en.m.wikipedia.org/wiki/Apollo_9">Apollo 9 </a>put the lunar module through its paces in Earth orbit,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979292%E2%80%93300-46">[45] </a> and in May <a href="https://en.m.wikipedia.org/wiki/Apollo_10">Apollo 10 </a>conducted a "dress rehearsal" in lunar orbit. By July 1969, all was in readiness for Apollo 11 to take the final step onto the Moon.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979303%E2%80%93312-47">[46] </a>

The Soviet Union appeared to be winning the Space Race by beating the US to firsts, but its early lead was overtaken by the US <a href="https://en.m.wikipedia.org/wiki/Project_Gemini">Gemini program </a>and Soviet failure to develop the <a href="https://en.m.wikipedia.org/wiki/N1_(rocket)">N1 launcher </a>, which would have been comparable to the Saturn V.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-48">[47] </a> The Soviets tried to beat the US to return lunar material to the Earth by means of <a href="https://en.m.wikipedia.org/wiki/Uncrewed_spacecraft">uncrewed probes </a>. On July 13, three days before Apollo 11's launch, the Soviet Union launched <a href="https://en.m.wikipedia.org/wiki/Luna_15">Luna 15 </a>, which reached lunar orbit before Apollo 11. During descent, a malfunction caused Luna 15 to crash in <a href="https://en.m.wikipedia.org/wiki/Mare_Crisium">Mare Crisium </a>about two hours before Armstrong and Aldrin took off from the Moon's surface to begin their voyage home. The <a href="https://en.m.wikipedia.org/wiki/Nuffield_Radio_Astronomy_Laboratories">Nuffield Radio Astronomy Laboratories </a>radio telescope in England recorded transmissions from Luna 15 during its descent, and these were released in July 2009 for the 40th anniversary of Apollo 11.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-49">[48] </a>

The initial crew assignment of Commander <a href="https://en.m.wikipedia.org/wiki/Neil_Armstrong">Neil Armstrong </a>, Command Module Pilot (CMP) <a href="https://en.m.wikipedia.org/wiki/Jim_Lovell">Jim Lovell </a>, and Lunar Module Pilot (LMP) <a href="https://en.m.wikipedia.org/wiki/Buzz_Aldrin">Buzz Aldrin </a>on the backup crew for Apollo  9 was officially announced on November 20, 1967.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979374-50">[49] </a> Lovell and Aldrin had previously flown together as the crew of <a href="https://en.m.wikipedia.org/wiki/Gemini_12">Gemini 12 </a>. Due to design and manufacturing delays in the LM, Apollo  8 and Apollo  9 swapped prime and backup crews, and Armstrong's crew became the backup for Apollo  8. Based on the normal crew rotation scheme, Armstrong was then expected to command Apollo 11.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005312%E2%80%93313-51">[50] </a>

There would be one change. <a href="https://en.m.wikipedia.org/wiki/Michael_Collins_(astronaut)">Michael Collins </a>, the CMP on the Apollo  8 crew, began experiencing trouble with his legs. Doctors diagnosed the problem as a bony growth between his fifth and sixth vertebrae, requiring surgery.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001288%E2%80%93289-52">[51] </a> Lovell took his place on the Apollo  8 crew, and when Collins recovered he joined Armstrong's crew as CMP. In the meantime, <a href="https://en.m.wikipedia.org/wiki/Fred_Haise">Fred Haise </a>filled in as backup LMP, and Aldrin as backup CMP for Apollo 8.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECunningham2010109-53">[52] </a> Apollo 11 was the second American mission where all the crew members had prior spaceflight experience,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff200090-54">[53] </a> the first being Apollo 10.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff200072-55">[54] </a> The next was <a href="https://en.m.wikipedia.org/wiki/STS-26">STS-26 </a>in 1988.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff200090-54">[53] </a>

<a href="https://en.m.wikipedia.org/wiki/Deke_Slayton">Deke Slayton </a>gave Armstrong the option to replace Aldrin with Lovell, since some thought Aldrin was difficult to work with. Armstrong had no issues working with Aldrin but thought it over for a day before declining. He thought Lovell deserved to command his own mission (eventually <a href="https://en.m.wikipedia.org/wiki/Apollo_13">Apollo 13 </a>).<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005338%E2%80%93339-56">[55] </a>

The Apollo 11 prime crew had none of the close cheerful camaraderie characterized by that of <a href="https://en.m.wikipedia.org/wiki/Apollo_12">Apollo 12 </a>. Instead, they forged an amiable working relationship. Armstrong in particular was notoriously aloof, but Collins, who considered himself a loner, confessed to rebuffing Aldrin's attempts to create a more personal relationship.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001434%E2%80%93435-57">[56] </a> Aldrin and Collins described the crew as "amiable strangers".<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005359-58">[57] </a> Armstrong did not agree with the assessment, and said "... all the crews I was on worked very well together."<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005359-58">[57] </a>

The backup crew consisted of Lovell as Commander, <a href="https://en.m.wikipedia.org/wiki/William_Anders">William Anders </a>as CMP, and Haise as LMP. Anders had flown with Lovell on Apollo  8.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff200090-54">[53] </a> In early 1969, he accepted a job with the <a href="https://en.m.wikipedia.org/wiki/National_Space_Council">National Aeronautics and Space Council </a>effective August 1969, and announced he would retire as an astronaut at that time. <a href="https://en.m.wikipedia.org/wiki/Ken_Mattingly">Ken Mattingly </a>was moved from the support crew into parallel training with Anders as backup CMP in case Apollo 11 was delayed past its intended July launch date, at which point Anders would be unavailable.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESlaytonCassutt1994237-59">[58] </a>

By the normal crew rotation in place during Apollo, Lovell, Mattingly, and Haise were scheduled to fly on <a href="https://en.m.wikipedia.org/wiki/Apollo_14">Apollo 14 </a>after backing up for Apollo 11. Later, Lovell's crew was forced to switch places with <a href="https://en.m.wikipedia.org/wiki/Alan_Shepard">Alan Shepard </a>'s tentative <a href="https://en.m.wikipedia.org/wiki/Apollo_13">Apollo 13 </a>crew to give Shepard more training time.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESlaytonCassutt1994237-59">[58] </a>

During Projects Mercury and Gemini, each mission had a prime and a backup crew. For Apollo, a third crew of astronauts was added, known as the support crew. The support crew maintained the flight plan, checklists and mission ground rules, and ensured the prime and backup crews were apprised of changes. They developed procedures, especially those for emergency situations, so these were ready for when the prime and backup crews came to train in the simulators, allowing them to concentrate on practicing and mastering them.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979261-60">[59] </a> For Apollo 11, the support crew consisted of Ken Mattingly, <a href="https://en.m.wikipedia.org/wiki/Ronald_Evans_(astronaut)">Ronald Evans </a>and <a href="https://en.m.wikipedia.org/wiki/William_R._Pogue">Bill Pogue </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979375-61">[60] </a>

The <a href="https://en.m.wikipedia.org/wiki/Capsule_communicator">capsule communicator </a>(CAPCOM) was an astronaut at the <a href="https://en.m.wikipedia.org/wiki/Christopher_C._Kraft_Jr._Mission_Control_Center">Mission Control Center </a>in <a href="https://en.m.wikipedia.org/wiki/Houston,_Texas">Houston, Texas </a>, who was the only person who communicated directly with the flight crew.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEKranz200027-62">[61] </a> For Apollo 11, the CAPCOMs were: <a href="https://en.m.wikipedia.org/wiki/Charles_Duke">Charles Duke </a>, Ronald Evans, <a href="https://en.m.wikipedia.org/wiki/Bruce_McCandless_II">Bruce McCandless II </a>, James Lovell, William Anders, Ken Mattingly, Fred Haise, <a href="https://en.m.wikipedia.org/wiki/Don_L._Lind">Don L. Lind </a>, <a href="https://en.m.wikipedia.org/wiki/Owen_K._Garriott">Owen K. Garriott </a>and <a href="https://en.m.wikipedia.org/wiki/Harrison_Schmitt">Harrison Schmitt </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979375-61">[60] </a>

Other key personnel who played important roles in the Apollo 11 mission include the following.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-69">[68] </a>

The Apollo 11 <a href="https://en.m.wikipedia.org/wiki/Mission_patch">mission emblem </a>was designed by Collins, who wanted a symbol for "peaceful lunar landing by the United States". At Lovell's suggestion, he chose the <a href="https://en.m.wikipedia.org/wiki/Bald_eagle">bald eagle </a>, the <a href="https://en.m.wikipedia.org/wiki/National_bird">national bird </a>of the United States, as the symbol. Tom Wilson, a simulator instructor, suggested an <a href="https://en.m.wikipedia.org/wiki/Olive_branch">olive branch </a>in its beak to represent their peaceful mission. Collins added a lunar background with the Earth in the distance. The sunlight in the image was coming from the wrong direction; the shadow should have been in the lower part of the Earth instead of the left. Aldrin, Armstrong and Collins decided the Eagle and the Moon would be in their natural colors, and decided on a blue and gold border. Armstrong was concerned that "eleven" would not be understood by non-English speakers, so they went with "Apollo 11",<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001332%E2%80%93334-70">[69] </a> and they decided not to put their names on the patch, so it would "be representative of everyone who had worked toward a lunar landing".<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001332-71">[70] </a>

An illustrator at the <a href="https://en.m.wikipedia.org/wiki/Manned_Spacecraft_Center">Manned Spacecraft Center </a>(MSC) did the artwork, which was then sent off to NASA officials for approval.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001332%E2%80%93334-70">[69] </a> The design was rejected. <a href="https://en.m.wikipedia.org/wiki/Bob_Gilruth">Bob Gilruth </a>, the director of the MSC felt the talons of the eagle looked "too warlike".<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001333-72">[71] </a> After some discussion, the olive branch was moved to the talons.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001333-72">[71] </a> When the <a href="https://en.m.wikipedia.org/wiki/Eisenhower_dollar">Eisenhower dollar coin </a>was released in 1971, the patch design provided the eagle for its reverse side.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-73">[72] </a> The design was also used for the smaller <a href="https://en.m.wikipedia.org/wiki/Susan_B._Anthony_dollar">Susan B. Anthony dollar </a>unveiled in 1979.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-74">[73] </a>

After the crew of Apollo 10 named their spacecraft Charlie Brown and Snoopy , assistant manager for public affairs <a href="https://en.m.wikipedia.org/wiki/Julian_Scheer">Julian Scheer </a>wrote to <a href="https://en.m.wikipedia.org/wiki/George_Low">George Low </a>, the Manager of the Apollo Spacecraft Program Office at the MSC, to suggest the Apollo 11 crew be less flippant in naming their craft. The name Snowcone was used for the CM and Haystack was used for the LM in both internal and external communications during early mission planning.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMarshall_Space_Flight_Center19698-75">[74] </a>

The LM was named <a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">Eagle </a> after the motif which was featured prominently on the mission insignia. At Scheer's suggestion, the CM was named <a href="https://en.m.wikipedia.org/wiki/Command_module_Columbia">Columbia </a> after <a href="https://en.m.wikipedia.org/wiki/Columbiad#In_fiction">Columbiad </a> , the giant cannon that launched a spacecraft (also from Florida) in <a href="https://en.m.wikipedia.org/wiki/Jules_Verne">Jules Verne </a>'s 1865 novel <a href="https://en.m.wikipedia.org/wiki/From_the_Earth_to_the_Moon">From the Earth to the Moon </a> . It also referred to <a href="https://en.m.wikipedia.org/wiki/Columbia_(name)">Columbia </a>, a historical name of the United States. <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001334%E2%80%93335-76">[75] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979331-77">[76] </a> In Collins' 1976 book, he said Columbia was in reference to <a href="https://en.m.wikipedia.org/wiki/Christopher_Columbus">Christopher Columbus </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins1994116-78">[77] </a>

The astronauts had <a href="https://en.m.wikipedia.org/wiki/Personal_preference_kit">personal preference kits </a>(PPKs), small bags containing personal items of significance they wanted to take with them on the mission.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-79">[78] </a> Five 0.5-pound (0.23 kg) PPKs were carried on Apollo 11: three (one for each astronaut) were stowed on Columbia before launch, and two on Eagle .<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-80">[79] </a>

Neil Armstrong's LM PPK contained a piece of wood from the <a href="https://en.m.wikipedia.org/wiki/Wright_brothers">Wright brothers </a>' 1903 <a href="https://en.m.wikipedia.org/wiki/Wright_Flyer">Wright Flyer </a> ' s left propeller and a piece of fabric from its wing,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005527-81">[80] </a> along with a diamond-studded <a href="https://en.m.wikipedia.org/wiki/Astronaut_pin">astronaut pin </a>originally given to Slayton by the widows of the Apollo  1 crew. This pin had been intended to be flown on that mission and given to Slayton afterwards, but following the disastrous launch pad fire and subsequent funerals, the widows gave the pin to Slayton. Armstrong took it with him on Apollo 11.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESlaytonCassutt1994191%E2%80%93192-82">[81] </a>

NASA's Apollo Site Selection Board announced five potential landing sites on February 8, 1968. These were the result of two years' worth of studies based on high-resolution photography of the lunar surface by the five uncrewed probes of the <a href="https://en.m.wikipedia.org/wiki/Lunar_Orbiter_program">Lunar Orbiter program </a>and information about surface conditions provided by the <a href="https://en.m.wikipedia.org/wiki/Surveyor_program">Surveyor program </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Site_Selection-83">[82] </a> The best Earth-bound telescopes could not resolve features with the resolution Project Apollo required.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECortright197579-84">[83] </a> The landing site had to be close to the lunar equator to minimize the amount of propellant required, clear of obstacles to minimize maneuvering, and flat to simplify the task of the landing radar. Scientific value was not a consideration.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHarland199919-85">[84] </a>

Areas that appeared promising on photographs taken on Earth were often found to be totally unacceptable. The original requirement that the site be free of craters had to be relaxed, as no such site was found.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECortright197598%E2%80%9399-86">[85] </a> Five sites were considered: Sites  1 and  2 were in the Sea of Tranquility (<a href="https://en.m.wikipedia.org/wiki/Mare_Tranquillitatis">Mare Tranquillitatis </a> ); Site  3 was in the Central Bay (<a href="https://en.m.wikipedia.org/wiki/Sinus_Medii">Sinus Medii </a> ); and Sites  4 and  5 were in the Ocean of Storms (<a href="https://en.m.wikipedia.org/wiki/Oceanus_Procellarum">Oceanus Procellarum </a> ).<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Site_Selection-83">[82] </a> The final site selection was based on seven criteria:

<ul><li>The site needed to be smooth, with relatively few craters; </li><li>with approach paths free of large hills, tall cliffs or deep craters that might confuse the landing radar and cause it to issue incorrect readings; </li><li>reachable with a minimum amount of propellant; </li><li>allowing for delays in the launch countdown; </li><li>providing the Apollo spacecraft with a free-return trajectory, one that would allow it to coast around the Moon and safely return to Earth without requiring any engine firings should a problem arise on the way to the Moon; </li><li>with good visibility during the landing approach, meaning the Sun would be between 7  and 20 degrees behind the LM; and </li><li>a general slope of less than two degrees in the landing area.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Site_Selection-83">[82] </a> </li> </ul>

The requirement for the Sun angle was particularly restrictive, limiting the launch date to one day per month.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Site_Selection-83">[82] </a> A landing just after dawn was chosen to limit the temperature extremes the astronauts would experience.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins19947-87">[86] </a> The Apollo Site Selection Board selected Site  2, with Sites 3  and  5 as backups in the event of the launch being delayed. In May 1969, Apollo 10's lunar module flew to within 15 kilometers (9.3 mi) of Site  2, and reported it was acceptable.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECappellari1972976-88">[87] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-89">[88] </a>

During the first press conference after the Apollo 11 crew was announced, the first question was, "Which one of you gentlemen will be the first man to step onto the lunar surface?"<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994148-90">[89] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005360-91">[90] </a> Slayton told the reporter it had not been decided, and Armstrong added that it was "not based on individual desire".<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994148-90">[89] </a>

One of the first versions of the egress checklist had the lunar module pilot exit the spacecraft before the commander, which matched what had been done on Gemini missions,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001347-92">[91] </a> where the commander had never performed the spacewalk.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEAldrinAbraham201657%E2%80%9358-93">[92] </a> Reporters wrote in early 1969 that Aldrin would be the first man to walk on the Moon, and Associate Administrator <a href="https://en.m.wikipedia.org/wiki/George_Mueller_(NASA)">George Mueller </a>told reporters he would be first as well. Aldrin heard that Armstrong would be the first because Armstrong was a civilian, which made Aldrin livid. Aldrin attempted to persuade other lunar module pilots he should be first, but they responded cynically about what they perceived as a lobbying campaign. Attempting to stem interdepartmental conflict, Slayton told Aldrin that Armstrong would be first since he was the commander. The decision was announced in a press conference on April 14, 1969.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005363%E2%80%93365-94">[93] </a>

For decades, Aldrin believed the final decision was largely driven by the lunar module's hatch location. Because the astronauts had their spacesuits on and the spacecraft was so small, maneuvering to exit the spacecraft was difficult. The crew tried a simulation in which Aldrin left the spacecraft first, but he damaged the simulator while attempting to egress. While this was enough for mission planners to make their decision, Aldrin and Armstrong were left in the dark on the decision until late spring.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994149-95">[94] </a> Slayton told Armstrong the plan was to have him leave the spacecraft first, if he agreed. Armstrong said, "Yes, that's the way to do it."<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994150-96">[95] </a>

The media accused Armstrong of exercising his commander's prerogative to exit the spacecraft first.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTESchefter1999281-97">[96] </a> <a href="https://en.m.wikipedia.org/wiki/Chris_Kraft">Chris Kraft </a>revealed in his 2001 autobiography that a meeting occurred between Gilruth, Slayton, Low, and himself to make sure Aldrin would not be the first to walk on the Moon. They argued that the first person to walk on the Moon should be like <a href="https://en.m.wikipedia.org/wiki/Charles_Lindbergh">Charles Lindbergh </a>, a calm and quiet person. They made the decision to change the flight plan so the commander was the first to egress from the spacecraft.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHansen2005371%E2%80%93372-98">[97] </a>

The ascent stage of <a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">LM-5 Eagle </a>arrived at the <a href="https://en.m.wikipedia.org/wiki/Kennedy_Space_Center">Kennedy Space Center </a>on January 8, 1969, followed by the descent stage four days later, and <a href="https://en.m.wikipedia.org/wiki/Command_module_Columbia">CSM-107 Columbia </a>on January 23.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Mission_Overview-5">[5] </a> There were several differences between Eagle and Apollo 10's LM-4 Snoopy ; Eagle had a VHF radio antenna to facilitate communication with the astronauts during their EVA on the lunar surface; a lighter ascent engine; more thermal protection on the landing gear; and a package of scientific experiments known as the <a href="https://en.m.wikipedia.org/wiki/Early_Apollo_Scientific_Experiments_Package">Early Apollo Scientific Experiments Package </a>(EASEP). The only change in the configuration of the command module was the removal of some insulation from the forward hatch.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978472-99">[98] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-100">[99] </a> The CSM was mated on January 29, and moved from the <a href="https://en.m.wikipedia.org/wiki/Operations_and_Checkout_Building">Operations and Checkout Building </a>to the <a href="https://en.m.wikipedia.org/wiki/Vehicle_Assembly_Building">Vehicle Assembly Building </a>on April 14.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Mission_Overview-5">[5] </a>

The <a href="https://en.m.wikipedia.org/wiki/S-IVB">S-IVB </a>third stage of Saturn V AS-506 had arrived on January 18, followed by the <a href="https://en.m.wikipedia.org/wiki/S-II">S-II </a>second stage on February 6, <a href="https://en.m.wikipedia.org/wiki/S-IC">S-IC </a>first stage on February 20, and the <a href="https://en.m.wikipedia.org/wiki/Saturn_V_Instrument_Unit">Saturn V Instrument Unit </a>on February 27. At 12:30 on May 20, the 5,443-tonne (5,357-long-ton; 6,000-short-ton) assembly departed the Vehicle Assembly Building atop the <a href="https://en.m.wikipedia.org/wiki/Crawler-transporter">crawler-transporter </a>, bound for Launch Pad 39A, part of <a href="https://en.m.wikipedia.org/wiki/Launch_Complex_39">Launch Complex 39 </a>, while Apollo 10 was still on its way to the Moon. A countdown test commenced on June 26, and concluded on July 2. The launch complex was floodlit on the night of July 15, when the crawler-transporter carried the <a href="https://en.m.wikipedia.org/wiki/Service_structure">mobile service structure </a>back to its parking area.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Mission_Overview-5">[5] </a> In the early hours of the morning, the fuel tanks of the S-II and S-IVB stages were filled with <a href="https://en.m.wikipedia.org/wiki/Liquid_hydrogen">liquid hydrogen </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978474-101">[100] </a> Fueling was completed by three hours before launch.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978475-102">[101] </a> Launch operations were partly automated, with 43 programs written in the <a href="https://en.m.wikipedia.org/wiki/ATOLL_(programming_language)">ATOLL programming language </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978355%E2%80%93356-103">[102] </a>

Slayton roused the crew shortly after 04:00, and they showered, shaved, and had the traditional pre-flight breakfast of steak and eggs with Slayton and the backup crew. They then donned their space suits and began breathing pure oxygen. At 06:30, they headed out to Launch Complex 39.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001355%E2%80%93357-104">[103] </a> Haise entered Columbia about three hours and ten minutes before launch time. Along with a technician, he helped Armstrong into the left-hand couch at 06:54. Five minutes later, Collins joined him, taking up his position on the right-hand couch. Finally, Aldrin entered, taking the center couch.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978475-102">[101] </a> Haise left around two hours and ten minutes before launch.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-AP11FJ-105">[104] </a> The closeout crew sealed the hatch, and the cabin was purged and pressurized. The closeout crew then left the launch complex about an hour before launch time. The countdown became automated at three minutes and twenty seconds before launch time.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978475-102">[101] </a> Over 450 personnel were at the consoles in the <a href="https://en.m.wikipedia.org/wiki/Firing_room">firing room </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978474-101">[100] </a>

An estimated one million spectators watched the launch of Apollo 11 from the highways and beaches in the vicinity of the launch site. Dignitaries included the <a href="https://en.m.wikipedia.org/wiki/Chief_of_Staff_of_the_United_States_Army">Chief of Staff of the United States Army </a>, <a href="https://en.m.wikipedia.org/wiki/General_(United_States)">General </a><a href="https://en.m.wikipedia.org/wiki/William_Westmoreland">William Westmoreland </a>, four <a href="https://en.m.wikipedia.org/wiki/Cabinet_of_the_United_States">cabinet members </a>, 19 <a href="https://en.m.wikipedia.org/wiki/Governor_(United_States)">state governors </a>, 40 <a href="https://en.m.wikipedia.org/wiki/Mayoralty_in_the_United_States">mayors </a>, 60 <a href="https://en.m.wikipedia.org/wiki/Ambassador">ambassadors </a>and 200 <a href="https://en.m.wikipedia.org/wiki/Congressmen">congressmen </a>. <a href="https://en.m.wikipedia.org/wiki/Vice_President_of_the_United_States">Vice President </a><a href="https://en.m.wikipedia.org/wiki/Spiro_Agnew">Spiro Agnew </a>viewed the launch with former president <a href="https://en.m.wikipedia.org/wiki/Lyndon_B._Johnson">Lyndon B. Johnson </a>and his wife <a href="https://en.m.wikipedia.org/wiki/Lady_Bird_Johnson">Lady Bird Johnson </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978474-101">[100] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBilstein1980369%E2%80%93370-106">[105] </a> Around 3,500 media representatives were present.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBrooksGrimwoodSwenson1979338-107">[106] </a> About two-thirds were from the United States; the rest came from 55 other countries. The launch was televised live in 33 countries, with an estimated 25 million viewers in the United States alone. Millions more around the world listened to radio broadcasts.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBilstein1980369%E2%80%93370-106">[105] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEBensonFaherty1978474-101">[100] </a> President <a href="https://en.m.wikipedia.org/wiki/Richard_Nixon">Richard Nixon </a>viewed the launch from his office in the <a href="https://en.m.wikipedia.org/wiki/White_House">White House </a>with his NASA liaison officer, Apollo astronaut <a href="https://en.m.wikipedia.org/wiki/Frank_Borman">Frank Borman </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-108">[107] </a>

Saturn V AS-506 launched Apollo 11 on July 16, 1969, at 13:32:00 <a href="https://en.m.wikipedia.org/wiki/UTC">UTC </a>(9:32:00 <a href="https://en.m.wikipedia.org/wiki/Eastern_Daylight_Time">EDT </a>).<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Mission_Overview-5">[5] </a> At 13.2 seconds into the flight, the launch vehicle began to <a href="https://en.m.wikipedia.org/wiki/Roll_program">roll </a>into its <a href="https://en.m.wikipedia.org/wiki/Flight_azimuth">flight azimuth </a>of 72.058°. Full shutdown of the first-stage engines occurred about 2  minutes and 42 seconds into the mission, followed by separation of the S-IC and ignition of the S-II engines. The second stage engines then cut off and separated at about 9  minutes and 8  seconds, allowing the first ignition of the S-IVB engine a few seconds later.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000106-7">[7] </a>

Apollo 11 entered a <a href="https://en.m.wikipedia.org/wiki/Elliptic_orbit">near-circular Earth orbit </a>at an altitude of 100.4 nautical miles (185.9 km) by 98.9 nautical miles (183.2 km), twelve minutes into its flight. After one and a half orbits, a second ignition of the S-IVB engine pushed the spacecraft onto its trajectory toward the Moon with the <a href="https://en.m.wikipedia.org/wiki/Trans-lunar_injection">trans-lunar injection </a>(TLI) burn at 16:22:13 UTC. About 30 minutes later, with Collins in the left seat and at the controls, the <a href="https://en.m.wikipedia.org/wiki/Transposition,_docking,_and_extraction">transposition, docking, and extraction </a>maneuver was performed. This involved separating Columbia from the spent S-IVB stage, turning around, and docking with Eagle still attached to the stage. After the LM was extracted, the combined spacecraft headed for the Moon, while the rocket stage flew on a trajectory past the Moon.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollins2001374%E2%80%93375-109">[108] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000106-7">[7] </a> This was done to avoid the third stage colliding with the spacecraft, the Earth, or the Moon. A <a href="https://en.m.wikipedia.org/wiki/Gravity_assist">slingshot effect </a>from passing around the Moon threw it into an <a href="https://en.m.wikipedia.org/wiki/Heliocentric_orbit">orbit around the Sun </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMarshall_Space_Flight_Center19697-110">[109] </a>

On July 19 at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter <a href="https://en.m.wikipedia.org/wiki/Lunar_orbit">lunar orbit </a>.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000106-7">[7] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-111">[110] </a> In the thirty orbits that followed, the crew saw passing views of their landing site in the southern Sea of Tranquility about 12 miles (19 km) southwest of the crater <a href="https://en.m.wikipedia.org/wiki/Collins_(crater)">Sabine D </a>. The site was selected in part because it had been characterized as relatively flat and smooth by the automated <a href="https://en.m.wikipedia.org/wiki/Ranger_8">Ranger 8 </a>and <a href="https://en.m.wikipedia.org/wiki/Surveyor_5">Surveyor 5 </a>landers and the Lunar Orbiter mapping spacecraft, and because it was unlikely to present major landing or EVA challenges.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-112">[111] </a> It lay about 25 kilometers (16 mi) southeast of the Surveyor  5 landing site, and 68 kilometers (42 mi) southwest of Ranger  8's crash site.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMission_Evaluation_Team1969130-113">[112] </a>

At 12:52:00 UTC on July 20, Aldrin and Armstrong entered <a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">Eagle </a>, and began the final preparations for lunar descent.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000106-7">[7] </a> At 17:44:00 Eagle separated from Columbia .<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000107-12">[12] </a> Collins, alone aboard Columbia , inspected Eagle as it pirouetted before him to ensure the craft was not damaged, and that the landing gear was correctly deployed.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMission_Evaluation_Team19699-114">[113] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollinsAldrin1975209-115">[114] </a> Armstrong exclaimed: "The Eagle has wings!"<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollinsAldrin1975209-115">[114] </a>

As the descent began, Armstrong and Aldrin found themselves passing landmarks on the surface two or three seconds early, and reported that they were "long"; they would land miles west of their target point. Eagle was traveling too fast. The problem could have been <a href="https://en.m.wikipedia.org/wiki/Mass_concentration_(astronomy)">mascons </a>—concen­tra­tions of high mass in a region or regions of the Moon's crust that contains a <a href="https://en.m.wikipedia.org/wiki/Gravity_anomaly">gravitational anomaly </a>, potentially altering Eagle 's trajectory. Flight Director Gene Kranz speculated that it could have resulted from extra air pressure in the docking tunnel. Or it could have been the result of Eagle ' s pirouette maneuver.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMindell2008220%E2%80%93221-116">[115] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMission_Evaluation_Team196982-117">[116] </a>

Five minutes into the descent burn, and 6,000 feet (1,800 m) above the surface of the Moon, the <a href="https://en.m.wikipedia.org/wiki/Apollo_Guidance_Computer">LM guidance computer </a>(LGC) distracted the crew with the first of several unexpected 1201 and 1202 program alarms. Inside Mission Control Center, computer engineer <a href="https://en.m.wikipedia.org/wiki/Jack_Garman">Jack Garman </a>told <a href="https://en.m.wikipedia.org/wiki/Flight_controller#GUIDO">Guidance Officer </a><a href="https://en.m.wikipedia.org/wiki/Steve_Bales">Steve Bales </a>it was safe to continue the descent, and this was relayed to the crew. The program alarms indicated "executive overflows", meaning the guidance computer could not complete all its tasks in real-time and had to postpone some of them.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTECollinsAldrin1975210%E2%80%93212-118">[117] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEHamiltonHackler200834%E2%80%9343-119">[118] </a> <a href="https://en.m.wikipedia.org/wiki/Margaret_Hamilton_(scientist)">Margaret Hamilton </a>, the Director of Apollo Flight Computer Programming at the <a href="https://en.m.wikipedia.org/wiki/MIT">MIT </a><a href="https://en.m.wikipedia.org/wiki/Charles_Stark_Draper_Laboratory">Charles Stark Draper Laboratory </a>later recalled:

To blame the computer for the Apollo 11 problems is like blaming the person who spots a fire and calls the fire department. Actually, the computer was programmed to do more than recognize error conditions. A complete set of recovery programs was incorporated into the software. The software's action, in this case, was to eliminate lower priority tasks and re-establish the more important ones. The computer, rather than almost forcing an abort, prevented an abort. If the computer hadn't recognized this problem and taken recovery action, I doubt if Apollo 11 would have been the successful Moon landing it was.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-120">[119] </a>

During the mission, the cause was diagnosed as the rendezvous radar switch being in the wrong position, causing the computer to process data from both the rendezvous and landing radars at the same time.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMission_Evaluation_Team1969190%E2%80%93192-121">[120] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-122">[121] </a> Software engineer <a href="https://en.m.wikipedia.org/wiki/Don_Eyles">Don Eyles </a>concluded in a 2005 Guidance and Control Conference paper that the problem was due to a hardware design bug previously seen during testing of the first uncrewed LM in <a href="https://en.m.wikipedia.org/wiki/Apollo_5">Apollo 5 </a>. Having the rendezvous radar on (so it was warmed up in case of an emergency landing abort) should have been irrelevant to the computer, but an electrical phasing mismatch between two parts of the rendezvous radar system could cause the stationary antenna to appear to the computer as dithering back and forth between two positions, depending upon how the hardware randomly powered up. The extra spurious <a href="https://en.m.wikipedia.org/wiki/Cycle_stealing">cycle stealing </a>, as the rendezvous radar updated an involuntary counter, caused the computer alarms.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-123">[122] </a>

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-foot-diameter (91 m) crater (later determined to be <a href="https://en.m.wikipedia.org/wiki/West_(lunar_crater)">West crater </a>), so he took semi-automatic control.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994196-124">[123] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMindell2008195%E2%80%93197-125">[124] </a> 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 107 feet (33 m) above the surface, Armstrong knew their propellant supply was dwindling and was determined to land at the first possible landing site.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994197-126">[125] </a>

Armstrong found a clear patch of ground and maneuvered the spacecraft towards it. As he got closer, now 250 feet (76 m) 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 100 feet (30 m) 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.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994198%E2%80%93199-127">[126] </a>

A light informed Aldrin that at least one of the 67-inch (170 cm) 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.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEChaikin1994199-128">[127] </a> Aldrin immediately said "Okay, engine stop. ACA—out of <a href="https://en.m.wikipedia.org/wiki/Detent">detent </a>." Armstrong acknowledged: "Out of detent. Auto." Aldrin continued: "Mode control—both auto. Descent engine command override off. Engine arm—off. 413 is in."<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEMindell2008226-129">[128] </a>

ACA was the <a href="https://en.m.wikipedia.org/wiki/Attitude_control">Attitude Control Assembly </a>—the LM's control stick. Output went to the LGC to command the <a href="https://en.m.wikipedia.org/wiki/Reaction_control_system">reaction control system </a>(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. LGC address 413 contained the variable that indicated the LM had landed.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-ALSJ_1-9">[9] </a>

Eagle landed at 20:17:40 UTC on Sunday July 20 with 216 pounds (98 kg) 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,<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-ALSJ_1-9">[9] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-FOOTNOTEOrloff2000295-130">[129] </a> but post-mission analysis showed that the real figure was probably closer to 50 seconds.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-Horizons2013-131">[130] </a> 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 sloshing more than expected, uncovering a fuel sensor. On subsequent missions, extra anti-slosh baffles were added to the tanks to prevent this.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-ALSJ_1-9">[9] </a>

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, <a href="https://en.m.wikipedia.org/wiki/Tranquility_Base">Tranquility Base </a>here. The <a href="https://en.m.wikipedia.org/wiki/Lunar_Module_Eagle">Eagle </a> has landed." Armstrong's unrehearsed change of call sign from "Eagle" to "Tranquility Base" emphasized to listeners that landing was complete and successful.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-132">[131] </a> Duke mispronounced his reply as he 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."<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-ALSJ_1-9">[9] </a> <a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-133">[132] </a>

Two and a half hours after landing, before preparations began for the EVA, Aldrin radioed to Earth:

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.<a href="https://en.m.wikipedia.org/wiki/Apollo_11#cite_note-134">[133] </a>

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