The Apollo program was a United States

human spaceflight Human spaceflight (also referred to as manned spaceflight or crewed spaceflight) is spaceflight with a crew or passengers aboard a spacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also be ...

program carried out from 1961 to 1972 by the

National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding th ...

(NASA), which landed the first

astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...

s on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. The program used the

Saturn IB The Saturn IB (also known as the uprated Saturn I) was an American launch vehicle commissioned by the NASA, National Aeronautics and Space Administration (NASA) for the Apollo program. It uprated the Saturn I by replacing the S-IV second stage (, ...

and

Saturn V Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, with multistage rocket, three stages, and powered with liquid-propellant r ...

launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload (spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pad, launch pads, supported by a missile launch contro ...

s to lift the Command/Service Module (CSM) and

Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...

(LM) spacecraft into space, and the

Little Joe II Little Joe II was an American rocket used from 1963 to 1966 for five uncrewed tests of the Apollo spacecraft launch escape system (LES), and to verify the performance of the command module parachute recovery system in abort mode. It was name ...

rocket to test a

launch escape system A launch escape system (LES) or launch abort system (LAS) is a crew-safety system connected to a space capsule that can be used to quickly separate the capsule from its launch vehicle in case of an emergency requiring the abort of the launch, suc ...

which was expected to carry the astronauts to safety in the event of a Saturn failure. Uncrewed test flights beginning in 1966 demonstrated the safety of the launch vehicles and spacecraft to carry astronauts, and four crewed flights beginning in October 1968 demonstrated the ability of the spacecraft to carry out a lunar landing mission. Apollo achieved the first crewed lunar landing on the

Apollo 11 Apollo 11 (July 16–24, 1969) was the American spaceflight that first landed humans on the Moon. Commander Neil Armstrong and lunar module pilot Buzz Aldrin landed the Apollo Lunar Module ''Eagle'' on July 20, 1969, at 20:17 UTC, an ...

mission, when

Neil Armstrong Neil Alden Armstrong (August 5, 1930 – August 25, 2012) was an American astronaut and aeronautical engineer who became the first person to walk on the Moon in 1969. He was also a naval aviator, test pilot, and university professor. ...

and

Buzz Aldrin Buzz Aldrin (; born Edwin Eugene Aldrin Jr.; January 20, 1930) is an American former astronaut, engineer and fighter pilot. He made three spacewalks as pilot of the 1966 Gemini 12 mission. As the Lunar Module ''Eagle'' pilot on the 1969 A ...

landed their LM ''Eagle'' in the

Sea of Tranquility Mare Tranquillitatis (Latin ''tranquillitātis'', the Sea of Tranquillity or Sea of Tranquility; see spelling differences) is a lunar mare that sits within the Tranquillitatis basin on the Moon. It is the first location on another world to be v ...

and walked on the lunar surface, while

Michael Collins Michael Collins or Mike Collins most commonly refers to: * Michael Collins (Irish leader) (1890–1922), Irish revolutionary leader, soldier, and politician * Michael Collins (astronaut) (1930–2021), American astronaut, member of Apollo 11 and Ge ...

remained in

lunar orbit In astronomy, lunar orbit (also known as a selenocentric orbit) is the orbit of an object around the Moon. As used in the space program, this refers not to the orbit of the Moon about the Earth, but to orbits by spacecraft around the Moon. The ...

in the CSM ''Columbia'', and all three landed safely on Earth on July 24, 1969. Five subsequent missions landed astronauts on various lunar sites, ending in December 1972 with twelve men having walked on the Moon and of lunar rocks and

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

samples returned to Earth, greatly contributing to the understanding of the Moon's composition and geological history. Two Apollo missions were failures: a 1967 cabin fire killed the entire

Apollo 1 Apollo 1, initially designated AS-204, was intended to be the first crewed mission of the Apollo program, the American undertaking to land the first man on the Moon. It was planned to launch on February 21, 1967, as the first low Earth orbita ...

crew during a ground test in preparation for what was to be the first crewed flight; and the third landing attempt on

Apollo 13 Apollo 13 (April 1117, 1970) was the seventh crewed mission in the Apollo space program and the third meant to land on the Moon. The craft was launched from Kennedy Space Center on April 11, 1970, but the lunar landing was aborted aft ...

was aborted by an oxygen tank explosion en route to the Moon, which disabled the CSM ''Odysseys electrical power and life support systems, and made the propulsion system unsafe to use. The crew circled the Moon and were returned safely to Earth using the LM ''Aquarius'' as a "lifeboat" for these functions.

Uncrewed test flights

From 1961 through 1967, Saturn launch vehicles and

Apollo spacecraft The Apollo spacecraft was composed of three parts designed to accomplish the American Apollo program's goal of landing astronauts on the Moon by the end of the 1960s and returning them safely to Earth. The expendable (single-use) spacecraft ...

components were tested in uncrewed flights.

Saturn I

The

Saturn I The Saturn I was a rocket designed as the United States' first medium lift launch vehicle for up to low Earth orbit payloads.Terminology has changed since the 1960s; back then, 20,000 pounds was considered "heavy lift". The rocket's first stag ...

launch vehicle was originally planned to carry crewed Command Module flights into

low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...

, but its payload capacity limit could not lift even a partially fueled Service Module, which would have required building a lightweight

retrorocket A retrorocket (short for ''retrograde rocket'') is a rocket engine providing thrust opposing the motion of a vehicle, thereby causing it to decelerate. They have mostly been used in spacecraft, with more limited use in short-runway aircraft land ...

module for deorbit. These plans were eventually scrapped, in favor of using the uprated

to launch the Command Module with a half-fueled Service Module for crewed Earth orbit tests. This limited Saturn I flights to Saturn launch vehicle development, CSM boilerplate testing, and three micrometeroid satellite launches in support of Apollo. There was some incongruity in the numbering and naming of the first three uncrewed Apollo-Saturn (AS), or Apollo flights. This is due to AS-204 being renamed to

posthumously. This crewed flight was to have followed the first three uncrewed flights. After the fire which killed the AS-204 crew on the pad during a test and training exercise, uncrewed Apollo flights resumed to test the Saturn V launch vehicle and the Lunar Module; these were designated Apollo 4, 5 and 6. The first crewed Apollo mission was thus Apollo 7. Simple "Apollo" numbers were never assigned to the first three uncrewed flights, although renaming

AS-201 AS-201 (or SA-201), flown February 26, 1966, was the first uncrewed test flight of an entire production Block I Apollo command and service module and the Saturn IB launch vehicle. The spacecraft consisted of the second Block I command module ...

AS-202 AS-202 (also referred to as SA-202) was the second uncrewed, suborbital test flight of a production Block I Apollo command and service module launched with the Saturn IB launch vehicle. It was launched on August 25, 1966, and was the first fl ...

, and

AS-203 AS-203 (or SA-203) was an uncrewed flight of the Saturn IB rocket on July 5, 1966. It carried no command and service module, as its purpose was to verify the design of the S-IVB rocket stage restart capability that would later be used in the A ...

as Apollo 1-A, Apollo 2 and Apollo 3, had been briefly considered.

Saturn IB

The Saturn I was converted to the Uprated Saturn I, eventually designated

, by replacing the

S-IV The S-IV was the second stage of the Saturn I rocket used by NASA for early flights in the Apollo program. The S-IV was manufactured by the Douglas Aircraft Company and later modified by them to the S-IVB, a similar but distinct stage used on t ...

second stage with the

S-IVB The S-IVB (pronounced "S-four-B") was the third stage on the Saturn V and second stage on the Saturn IB launch vehicles. Built by the Douglas Aircraft Company, it had one J-2 (rocket engine), J-2 rocket engine. For lunar missions it was fired twi ...

, which would also be used as the third stage of the Saturn V with the addition of on-orbit restart capability. This increased the payload capacity to , enough to orbit a Command Module with a half-fueled Service Module, and more than enough to orbit a fully fueled Lunar Module. Two suborbital tests of the Apollo Block I Command and Service Module, one S-IVB development test, and one Lunar Module test were conducted. Success of the LM test led to cancellation of a planned second uncrewed flight.

Launch escape system tests

From August 1963 to January 1966, a number of tests were conducted at the

White Sands Missile Range White Sands Missile Range (WSMR) is a United States Army military testing area and firing range located in the US state of New Mexico. The range was originally established as the White Sands Proving Ground on 9July 1945. White Sands National P ...

for development of the

(LES). These included simulated "pad aborts", which might occur while the Apollo-Saturn

space vehicle A space vehicle is the combination of a spacecraft and its launch vehicle which carries it into space. The earliest space vehicles were expendable launch systems, using a single or multistage rocket to carry a relatively small spacecraft in p ...

was still on the

launch pad A launch pad is an above-ground facility from which a rocket-powered missile or space vehicle is vertically launched. The term ''launch pad'' can be used to describe just the central launch platform (mobile launcher platform), or the entire ...

, and flights on the

rocket to simulate Mode I aborts which might occur while the vehicle was in the air.

Saturn V

Prior to George Mueller's tenure as NASA's Associate Administrator for Manned Space Flight starting in 1963, it was assumed that 20

s, with at least 10 unmanned test flights, would be required to achieve a crewed Moon landing, using the conservative one-stage-at-a-time testing philosophy used for the Saturn I. But Mueller introduced the "all-up" testing philosophy of using three live stages plus the Apollo spacecraft on every test flight. This achieved development of the Saturn V with far fewer uncrewed tests, and facilitated achieving the Moon landing by the 1969 goal. The size of the Saturn V production lot was reduced from 20 to 15 units. Three uncrewed test flights were planned to human-rate the super heavy-lift

which would take crewed Apollo flights to the Moon. Success of the first flight and qualified success of the second led to the decision to cancel the third uncrewed test.

Alphabetical mission types

The Apollo program required sequential testing of several major mission elements in the runup to a crewed lunar landing. An alphabetical list of major mission types was proposed by

Owen Maynard Owen Eugene Maynard (October 27, 1924 – July 15, 2000) was a Canadians, Canadian engineer who contributed to the designs of the Canadian CF-105 Avro Arrow jet interceptor, and of NASA's Apollo program, Apollo Lunar Module (LM). Maynard was a mem ...

in September 1967. Two "A-type" missions performed uncrewed tests of the CSM and the Saturn V, and one B-type mission performed an uncrewed test of the LM. The C-type mission, the first crewed flight of the CSM in Earth orbit, was performed by Apollo 7. The list was revised upon

George Low George Michael Low (born Georg Michael Löw, June 10, 1926 – July 17, 1984) was an administrator at NASA and the 14th president of Rensselaer Polytechnic Institute. Low was one of the senior NASA officials who made numerous decisions as m ...

's proposal to commit a mission to lunar orbit ahead of schedule, an idea influenced by the status of the CSM as a proven craft and production delays of the LM. Apollo 8 was reclassified from its original assignment as a D-type mission, a test of the complete CSM/LM spacecraft in Earth orbit, to a "C-prime" mission which would fly humans to the Moon. Once complete, it obviated the need for the E-type objective of a

medium Earth orbit A medium Earth orbit (MEO) is an geocentric orbit, Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between above sea level.

al test. The D-type mission was instead performed by Apollo 9; the F-type mission, Apollo 10, flew the CSM/LM spacecraft to the Moon for final testing, without landing. The G-type mission, Apollo 11, performed the first lunar landing, the central goal of the program. The initial A-G list was expanded to include later mission types: H-type missions—Apollo 12, 13 (planned) and 14—would perform precision landings, and J-type missions—Apollo 15, 16 and 17—would perform thorough scientific investigation. The I-type objective, which called for extended lunar orbital surveillance of the Moon, was incorporated into the J-type missions.

Crewed missions

The Block I CSM spacecraft did not have capability to fly with the LM, and the three crew positions were designated Command Pilot, Senior Pilot, and Pilot, based on U.S. Air Force pilot ratings. The Block II spacecraft was designed to fly with the Lunar Module, so the corresponding crew positions were designated Commander, Command Module Pilot, and Lunar Module Pilot regardless of whether a Lunar Module was present or not on any mission. Seven of the missions involved

extravehicular activity Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable Earthlike atmosphere, the astronaut is completely reliant on a space suit for environmental support. EVA in ...

(EVA), spacewalks or moonwalks outside of the spacecraft. These were of three types: testing the lunar EVA suit in Earth orbit (

Apollo 9 Apollo 9 (March 313, 1969) was the third human spaceflight in NASA's Apollo program. Flown in low Earth orbit, it was the second crewed Apollo mission that the United States launched via a Saturn V rocket, and was the first flight of the ful ...

), exploring the lunar surface, and retrieving film canisters from the

Scientific Instrument Module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo (spacecraft), Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functio ...

stored in the Service Module.

Canceled missions

Several planned missions of the Apollo program were canceled for a variety of reasons, including changes in technical direction, the Apollo 1 fire, hardware delays, and budget limitations. * Before the Apollo 1 fire, two crewed Block I spacecraft missions were planned, but then it was decided that the second one would give no more information about the spacecraft performance not obtained from the first, and could not carry out extra activities such as EVA, and was canceled. * The Saturn V's all-up testing strategy and relatively good success rate accomplished the first Moon landing on the sixth flight, leaving ten available for Moon landings through Apollo 20, but waning public interest in the program led to decreased Congressional funding, forcing NASA to economize. First, was cut to make a Saturn V available to launch the

Skylab Skylab was the first United States space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three separate three-astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Major operations in ...

space station whole instead of building it on-orbit using multiple Saturn IB launches. Eight months later, Apollo 18 and 19 were also cut to further economize, and because of fears of increased chance of failure with a large number of lunar flights.

Notes

References

Bibliography

External links

NASA page on Apollo Missions

* ttp://www.space.com/12771-nasa-apollo-missions-photo-countdown.html Space.com List of Apollo Missions.
AstronomyToday List of Missions

Project Apollo Flickr Photo Archive
{{Use American English, date=January 2014 *

Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...