200px|right|Apollo program insignia

The '''Apollo program''' was a human spaceflight program undertaken by NASA during the years 1961 – 1975 with the goal of conducting manned moon landing missions. President John F. Kennedy announced this goal in 1961, and it was accomplished on July 20 1969 by Neil Armstrong and Buzz Aldrin during the ''Apollo 11'' mission. Five other Apollo missions also landed astronauts on the Moon, the last one in 1972. These six Apollo spaceflights are the only times humans have landed on another celestial body.  The Apollo program, specifically the lunar landings, is often cited as the greatest achievement in human history.<ref>[http://history.nasa.gov/ap11ann/introduction.htm NASA: 30th Anniversary of Apollo 11]</ref><ref>[http://news.bbc.co.uk/1/hi/special_report/1999/07/99/the_moon_landing/396037.stm BBC: 30th Anniversary of Apollo 11]</ref>

Apollo was the third human spaceflight program undertaken by NASA, the Saturn launch vehicles, which were later used for the Skylab program and the joint American-Soviet Apollo-Soyuz Test Project. These later programs are thus often considered to be part of the overall Apollo program. 

The goal of the program, as articulated by President Kennedy, was accomplished with only two major failures. The first failure resulted in the deaths of three astronauts, Ed White and Roger Chaffee, in the Apollo 1 launchpad fire. The second was an in-space explosion on Apollo 13, which badly damaged the spacecraft on the moonward leg of its journey. The three astronauts aboard narrowly escaped with their lives, thanks to the efforts of flight controllers, project engineers, backup crew members and the skills of the astronauts themselves.

The program set major milestones in the history of human spaceflight. This program remains alone in sending manned missions beyond low Earth orbit. Apollo 8 was the first manned spacecraft to orbit another celestial body, while Apollo 17 marks the time of the last moonwalk and also the last manned mission beyond low Earth orbit.

The program spurred advances in many areas of technology peripheral to rocketry and manned spaceflight. These include major contributions in the fields of reliability of complex systems made from component parts. The physical facilities and machines which were necessary components of the manned spaceflight program remain as landmarks of civil, mechanical, and electrical engineering.

Many objects and artifacts from the program are on display at various locations throughout the world, notably at the Smithsonian's Air and Space Museums. 

==Background==

The Apollo program was originally conceived early in 1960, during the Eisenhower administration, as a follow-up to America's Mercury program. While the Mercury capsule could only support one astronaut on a limited earth orbital mission, the Apollo spacecraft was intended to be able to carry three astronauts on a circumlunar flight and perhaps even on a lunar landing. The program was named after the Greek god of light and archery by NASA manager Abe Silverstein, who later said that "I was naming the spacecraft like I'd name my baby."<ref>Murray and Cox, ''Apollo'', p. 55.</ref> While NASA went ahead with planning for Apollo, funding for the program was far from certain, particularly given Eisenhower's equivocal attitude to manned spaceflight.<ref>Murray and Cox, ''Apollo'', p. 60.</ref>
In November 1960, James Webb requested a thirty percent budget increase for his agency, Kennedy supported an acceleration of NASA's large booster program but deferred a decision on the broader issue.<ref>Beschloss, 'Kennedy and the Decision to Go to the Moon,' p. 55.</ref>

On  "Memorandum for Vice President,"] [[April 20,  "Evaluation of Space Program,"] [[April 21, 1961.</ref> His memo concluded that a manned moon landing was far enough in the future to make it possible that the United States could achieve it first.<ref name="lbjmemo"/>

thumb|left|The Decision to Go to the Moon: President John F. Kennedy's May 25, 1961 speech before a Joint Session of Congress
On May 25, 1961, Kennedy announced his support for the Apollo program as part of a special address to a joint session of Congress:
{{cquote|First, 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. No single space project in this period will be more impressive to mankind, or more important in the long-range exploration of space; and none will be so difficult or expensive to accomplish.
John F. Kennedy<ref name="Special Message">John F. Kennedy, [http://www.jfklibrary.org/Historical+Resources/Archives/Reference+Desk/Speeches/JFK/Urgent+National+Needs+Page+4.htm "Special Message to the Congress on Urgent National Needs"], May 25 1961</ref>
}}

At the time of Kennedy's speech, only one American had flown in space — less than a month earlier — and NASA had not yet sent a man into orbit. Some NASA employees doubted whether Kennedy's ambitious goal could be met.<ref>Murray and Cox, ''Apollo'', pp. 16-17.</ref>

Answering President Kennedy's challenge and landing men on the moon by the end of 1969 required the most sudden burst of technological creativity, and the largest commitment of resources ($25 billion), ever made by any nation in peacetime. At its peak, the Apollo program employed 400,000 Americans and required the support of over 20,000 industrial firms and universities.<ref>[http://www.nasa.gov/centers/langley/news/factsheets/Apollo.html|NASA Langley Research Center's Contributions to the Apollo Program]</ref>

thumbnail|right|President [[John F. Kennedy delivers a speech at Rice University on the subject of the American space program, September 12, 1962.]]
{{Cquote|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 which we intend to win, and the others, too.
John F. Kennedy<ref name="Rice Speech">John F. Kennedy,[http://www.jfklibrary.org/Historical+Resources/Archives/Reference+Desk/Speeches/JFK/003POF03SpaceEffort09121962.htm "Address at Rice University on the Nation's Space Effort"]</ref>}}

==Choosing a mission mode==

Once Kennedy had defined a goal, the Apollo mission planners were faced with the challenge of designing a set of flights that could meet this stated goal while minimizing risk to human life, cost, and demands on technology and astronaut skill. Four possible mission modes were considered:
thumb|left|Early Apollo configuration for <br />Direct Ascent and<br /> Earth Orbit Rendezvous - 1961 (NASA)
* '''Direct Ascent:''' A spacecraft would travel directly to the Moon, landing and returning as a unit. This plan would have required a very powerful booster, the planned Nova rocket.
* '''Earth Orbit Rendezvous (EOR):''' Two Saturn V rockets would be launched, one carrying the spacecraft and one carrying a propulsion unit that would have enabled the spacecraft to escape earth orbit. After a docking in earth orbit, the spacecraft would have landed on the Moon as a unit.
* '''Lunar Surface Rendezvous:''' Two spacecraft would be launched in succession. The first, an automated vehicle carrying propellants, would land on the Moon and would be followed some time later by the manned vehicle. Propellant would be transferred from the automated vehicle to the manned vehicle before the manned vehicle could return to Earth.
* '''Lunar Orbit Rendezvous (LOR):''' One Saturn V would launch a spacecraft that was composed of modular parts. A command module would remain in orbit around the moon, while a lunar module would descend to the moon and then return to dock with the command module while still in lunar orbit. In contrast with the other plans, LOR required only a small part of the spacecraft to land on the Moon, thereby minimizing the mass to be launched from the Moon's surface for the return trip.

In early 1961, direct ascent was generally the mission mode in favor at NASA. Many engineers feared that a rendezvous, which had never been attempted in space, would be impossible in lunar orbit. However, dissenters including John Houbolt at Langley Research Center emphasized the important weight reductions that were offered by the LOR approach. Throughout 1960 and 1961, Houbolt campaigned for the recognition of LOR as a valid and practical option. Bypassing the NASA hierarchy, he sent a series of memos and reports on the issue to Associate Administrator Robert Seamans; while acknowledging that he spoke "somewhat as a voice in the wilderness," Houbolt pleaded that LOR should not be discounted in studies of the question.<ref>Brooks, Grimwood and Swenson, ''Chariots for Apollo'', p. 71.</ref>

Seamans' establishment of the Golovin committee in July 1961 represented a turning point in NASA's mission mode decision.<ref name="hansen21"> Hansen, ''Enchanted Rendezvous'', p 21</ref> While the ad-hoc committee was intended to provide a recommendation on the boosters to be used in the Apollo program, it recognized that the mode decision was an important part of this question. The committee recommended in favor of a hybrid EOR-LOR mode, but its consideration of LOR — as well as Houbolt's ceaseless work — played an important role in publicizing the workability of the approach. In late 1961 and early 1962, members of NASA's Space Task Group at the Manned Spacecraft Center in Houston began to come around to support for LOR.<ref name="hansen21"/> The engineers at Marshall Space Flight Center took longer to become convinced of its merits, but their conversion was announced by Wernher von Braun at a briefing in June 1962. NASA's formal decision in favor of LOR was announced on July 11, 1962. Space historian James Hansen concludes that:

==Spacecraft==

The decision in favor of lunar orbit rendezvous dictated the basic design of the Command/Service Module (CSM), in which the crew would spend most of the mission, and the  Lunar Module (LM), which would descend to and return from the lunar surface.

===Command/service module===
thumb|right|Apollo CSM in lunar orbit.
The command module (CM) was conical in shape, and was designed to carry three astronauts from launch into lunar orbit and back from the moon to splashdown. Equipment carried by the command module included reaction control engines, a docking tunnel, guidance and navigation systems and the service module (SM), which housed the service propulsion system and its propellants, the fuel cell power system, four maneuvering thruster quads, the S-band antenna for communication with Mission Control, and storage tanks for water and air. On Apollo 15, 16 and 17 it also carried a scientific instrument package. The two sections of the spacecraft would remain attached until just prior to re-entry, at which point the service module would be discarded. Only the command module was provided with a heat shield that would allow it and its passengers to survive the intense heat of re-entry. After re-entry it would deploy parachutes that would slow its descent through the atmosphere, allowing a smooth splashdown in the ocean.

Under the leadership of Harrison Storms, North American Aviation won the contract to build the CSM for NASA. Relations between North American and NASA were strained during the Apollo program, particularly after the Apollo 1 fire during which three astronauts died. The cause of the accident was determined to be an electrical short in the wiring of the command module; while determination of responsibility for the accident was complex, the review board concluded that "deficiencies existed in Command Module design, workmanship and quality control."<ref>[http://www.hq.nasa.gov/office/pao/History/Apollo204/find.html| Report of the Apollo 204 Review Board, Findings and Recommendations]</ref>

===Lunar module===
thumb|left|Apollo LM on lunar surface.
The Lunar Module (LM) (also known as Lunar Excursion Module, or LEM), was designed solely in order to land on the moon, and to ascend from the lunar surface to the command module. It had a limited heat shield and was of a construction so lightweight that it would not have been able to fly in Earth gravity. It carried two crewmembers and consisted of two stages, a descent and an ascent stage. The descent stage incorporated compartments in which cargo such as the Apollo Lunar Surface Experiment Package and Lunar Rover could be carried.

The contract for design and construction of the lunar module was awarded to Tom Kelly. There were also problems with the lunar module; due to delays in the test program, the LM became what was known as a "pacing item," meaning that it was in danger of delaying the schedule of the whole Apollo program.<ref>[http://www.hq.nasa.gov/office/pao/History/SP-4205/ch7-4.html| Chariots for Apollo, Ch 7-4]</ref> Due to these issues, the Apollo missions were rescheduled so that the first manned mission with the lunar module would be Apollo 9, rather than Apollo 8 as was originally planned.
<br clear=all/>

==Boosters==
When the team of engineers led by Wernher von Braun began planning for the Apollo program, it was not yet clear what sort of mission their rocket boosters would have to support. Direct ascent would require a booster, the planned Nova rocket, which could lift a very large payload. NASA's decision in favor of lunar orbit rendezvous re-oriented the work of Marshall Spaceflight Center towards the development of the Saturn 1B and Saturn V. While these were less powerful than the Nova would have been, the Saturn V was still much more powerful than any booster developed before—or since.

===Saturn V===

thumb|right|The [[Saturn V rocket launched ''thumb|left|Saturn V diagram from the Apollo 6 press kitThe Saturn V consisted of three stages and an Instrument Unit which contained the booster's guidance system. The first stage, the S-IC, consisted of five F-1 engines arranged in a cross pattern, which produced a total of 7.5 million pounds of thrust. They burned for only 2.5 minutes, accelerating the spacecraft to a speed of approximately 6000 miles per hour (2.68 km/sec).<ref> Saturn V News Reference: First Stage Fact Sheet</ref> During development, the F-1 engines were plagued by combustion instability—if the combustion of propellants was not uniform across the flame front of an engine, pressure waves could build which would cause the engine to destroy itself. The problem was solved in the end through trial and error, fine-tuning the engines through numerous tests so that even small charges set off inside the engine would not induce instability.<ref>Murray and Cox, ''Apollo'', pp. 145-51, 179-81.</ref>

The second stage, the J-2 engines. They burned for approximately six minutes, taking the spacecraft to a speed of 15,300 miles per hour (6.84 km/sec) and an altitude of about <span style="white-space:nowrap">115&nbsp;miles&nbsp;(185&nbsp;km)</span>.<ref> Saturn V News Reference: Second Stage Fact Sheet</ref> At this point the translunar injection burn.<ref>Saturn V News Reference: Third Stage Fact Sheet</ref>

===Saturn IB===

The H-1 engines and a second S-IVB stage which was identical to the Saturn V's third stage. The Saturn IB had only 1.6 million pounds of thrust in its first stage—compared to 7.5 million pounds for the Saturn V—but was capable of putting a command and lunar module into earth orbit.<ref> Saturn IB News Reference: Saturn IB Design Features</ref> It was used in Apollo test missions and in both the Skylab program and the Apollo-Soyuz Test Program. In 1973 a refitted S-IVB stage, launched by a Saturn V, became the Skylab space station.

==Missions==

===Mission types===
In September 1967, the Manned Spacecraft Center in Houston, Texas, proposed a series of missions that would lead up to a manned lunar landing. Seven mission types were outlined, each testing a specific set of components and tasks; each previous step needed to be completed successfully before the next mission type could be undertaken. These were:
* '''A''' - Unmanned Command/Service Module (CSM) test
* '''B''' - Unmanned Lunar Module (LM) test
* '''C''' - Manned CSM in low Earth orbit
* '''D''' - Manned CSM and LM in low Earth orbit
* '''E''' - Manned CSM and LM in an elliptical Earth orbit with an apogee of 4600 mi (7400 km)
* '''F''' - Manned CSM and LM in lunar orbit
* '''G''' - Manned lunar landing

Later added to this were H missions, which were short duration stays on the Moon with two LEVAs ("moonwalks"). These were followed by the J missions, which were longer three day stays, with three LEVAs and the use of the lunar rover. ''Apollo 18'' to ''20'' would have been J missions. In addition, a further group of flights — the I missions — were planned, which would have been long duration orbital missions using a Service Module bay loaded with scientific equipment. When it became obvious that later flights were being cancelled, such mission plans were brought into the J missions that were actually flown.

===Unmanned missions===
Preparations for the Apollo program began long before the manned Apollo missions were flown. Test flights of the boilerplate models of the Apollo command/service module. Two pad abort tests of the launch escape system took place in 1963 and 1965 at the White Sands Missile Range.

The only unmanned missions to officially include Apollo as part of their name rather than serial number were Apollo 4, Apollo 5 and Apollo 6.<ref>Murray and Cox, ''Apollo'', p. 238.</ref> Apollo 4 was the first test flight of the Saturn V booster. Launched on November 9, 1967, Apollo 4 exemplified George Mueller's strategy of "all up" testing. Rather than being tested stage by stage, as most rockets were, the Saturn V would be flown for the first time as one unit. The mission was a highly successful one. Walter Cronkite covered the launch from a broadcast booth about 4 miles (6 km) from the launch site. The extreme noise and vibrations from the launch nearly shook the broadcast booth apart- ceiling tiles fell and windows shook. At one point, Cronkite was forced to dampen the vibrations in the booth's plate glass window to prevent it from shattering.<ref>Murray and Cox, ''Apollo'', p. 248.</ref> This launch showed that additional protective measures against the shock wave were necessary to protect structures in the immediate vicinity. Future launches used a damping mechanism directly at the launchpad which proved effective in confining the main effects of the shock wave to the blast area.<ref>Apollo_4#Flight</ref>.

Apollo 6 was the last in the series of unmanned Apollo missions. It launched on UTC.

===Manned missions===

<!-- Deleted image removed: thumb|A Turkish newspaper [[Hürriyet, July 21 1969]] -->

Apollo 7, launched on October 11, 1968 was the first manned mission in the Apollo program. It was an eleven-day Earth-orbital mission intended to test the redesigned command module.  It was the first manned launch of the Saturn IB launch vehicle, and the first three-man American space mission.

By the summer of 1968 it became clear to program managers that a fully functional LM would not be available for the Zond spacecraft around the moon, there is no evidence that this was actually the case. NASA officials were aware of the Soviet Zond flights, but the timing of the Zond missions does not correspond well with the extensive written record from NASA about the Apollo 8 decision. It is relatively certain that the Apollo 8 decision was primarily based upon the LM schedule, rather than fear of the Soviets beating the Americans to the moon.

Between December 21, 1968 and May 18, 1969, NASA launched three Apollo missions (8, 9, and 10) using the Saturn V launch vehicle. Each mission had a crew of three astronauts, and the last two included Lunar Modules, but none of these were intended as Moon landing missions.

thumb|left|A [[Apollo TV camera|mounted camera captures thumb|right|This image shows Apollo 11 astronaut Buzz Aldrin with the [[Flag of the United States|U.S. flag. The illusion of a breeze was caused by the horizontal rod intended to hold the flag flat failing to telescope out completely, thus leaving ripples in the fabric like those seen in a flag in the wind.]]
{{Cquote|That's one small step for [a] man, one giant leap for mankind.
Neil Armstrong<ref>Neil Armstrong#First_Moon_walk</ref>}}

The next two flights (11 and 12) included successful Moon landings. The Apollo 13 mission was aborted before the landing attempt, but the crew returned safely to Earth. The four subsequent Apollo missions (14 through 17) included successful Moon landings. The last three of these were J-class missions that included the use of Lunar Rovers. It appears that much of the original film and telemetry data for the Apollo 11 mission is missing. For more information see Apollo program missing tapes.

thumb|left|On the last of the [[List of Apollo missions|Apollo missions, the crew of Apollo 17 left this plaque as was done on all the previous landings.]] Apollo 17 launched December 7, 1972 and was the last Apollo mission to the moon. Mission commander Eugene Cernan was the last person to leave the Moon's surface. The crew returned safely to Earth on December 19, 1972.

שמאל|ממוזער|150px|סמל תוכנית אפולו
'''תוכנית אפולו''' (באנגלית: '''Project Apollo''') הייתה תוכנית שאפתנית שבוצעה על ידי שנות ה־60 ושנות ה־70 של המאה ה־20, להנחתת אדם על הירח והשבתו בשלום.

בעיקרו של דבר, תוכנית אפולו הייתה אחת החזיתות במלחמה הקרה שהתנהלה בין ארצות הברית וברית המועצות מתום מלחמת העולם השנייה ועד נפילת ברית המועצות בראשית שנות ה־90 של המאה ה־20. בחזית זו, שנקראה גם המירוץ לחלל, התחרו שתי המעצמות על הישגים בתחום כיבוש החלל. לאחר שברית המועצות השיגה את ארצות הברית בהכנסת האדם הראשון למסלול סביב כדור הארץ ב־12 באפריל 1961, הכריז נשיא ארצות הברית ג'ון קנדי, על תוכנית לשליחת אדם אל הירח לפני תום העשור:

בנאום מפורסם אחר, הסביר הנשיא מדוע על ארצות הברית להוביל את המירוץ לחלל:

יש לציין שתוכנית החלל האמריקאית החלה עוד לפני הנשיא קנדי. הנשיא דווייט אייזנהאואר החל בה, עם תוכנית מרקורי.

==מטרות==

רשמית, מטרות התוכנית היו כדלהלן:
*להשיג את הטכנולוגיה להשגת מטרות אחרות של ארצות הברית בחלל,
*להשיג עליונות בחלל,
*לבצע תוכנית מחקר מדעי על הירח,
*לפתח את היכולת לעבוד בסביבה הירחית.

==מבנה החללית==

חלליות אפולו הורכבו משלושה חלקים עיקריים:
#'''מודול הפיקוד''', שהכיל את מגורי הצוות ובקרת הטיסה.
#'''מודול השירות''', שהכיל את מערכות ההנעה ומערכות התמיכה בחללית.
#'''מודול הירח''', שנשא שניים מאנשי הצוות אל פני הירח, שימש אותם שם, והחזיר אותם אל שני המודולים הראשונים המחוברים זה לזה.

שיטת הטיסה נבחרה בשנת 1962. החללית נישאה על טיל סטורן 1B במשימות הראשונות, שהקיפו את כדור הארץ, וטיל סטורן 5 במשימות שהגיעו אל הירח.