The Apollo program was a United States human spaceflight program carried out from 1961 to 1972 by the National Aeronautics and Space Administration (NASA), which landed the first astronauts on the Moon.^[1] The program used the Saturn IB and Saturn V launch vehicles to lift the Command/Service Module (CSM) and Lunar Module (LM) spacecraft into space, and the Little Joe II rocket to test a launch escape system which was expected to carry the astronauts to safety in the event of a Saturn failure.^[2] 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 mission, when Neil Armstrong and Buzz Aldrin landed their LM Eagle in the Sea of Tranquility and walked on the lunar surface, while Michael Collins remained in lunar orbit in the CSM Columbia, and all three landed safely on Earth on July 24, 1969.^[3] Five subsequent missions landed astronauts on various lunar sites, ending in December 1972 with twelve men having walked on the Moon^[4] and 842 pounds (382 kg) of lunar rocks and soil samples returned to Earth, greatly contributing to the understanding of the Moon's composition and geological history.^[5]

Two Apollo missions were failures: a 1967 cabin fire killed the entire Apollo 1 crew during a ground test in preparation for what was to be the first crewed flight;^[6] and the third landing attempt on Apollo 13 was aborted by an oxygen tank explosion en route to the Moon, which disabled the CSM Odyssey's 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.^[7]

Uncrewed test flights

From 1961 through 1967, Saturn launch vehicles and Apollo spacecraft components were tested in uncrewed flights.

Saturn I

The Saturn I launch vehicle was originally planned to carry crewed Command Module flights into low Earth orbit, but its 20,000-pound (9,100 kg) payload capacity limit could not lift even a partially fueled Service Module, which would have required building a lightweight retrorocket module for deorbit. These plans were eventually scrapped, in favor of using the uprated Saturn IB 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 Apollo 1 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-202, and AS-203 as Apollo 1-A, Apollo 2 and Apollo 3, had been briefly considered.^[6]

Saturn IB

The Saturn I was converted to the Uprated Saturn I, eventually designated Saturn IB, by replacing the S-IV second stage with the S-IVB, 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 46,000 pounds (21,000 kg), 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 for development of the launch escape system (LES). These included simulated "pad aborts", which might occur while the Apollo-Saturn space vehicle was still on the launch pad, and flights on the Little Joe II rocket to simulate Mode I aborts which might occur while the vehicle was in the air.^[1]

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 Saturn Vs, with at least 10 unpiloted 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.^[10]

Three uncrewed test flights were planned to human-rate the super heavy-lift Saturn V 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 in September 1967.^[11][12] 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'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.^[13] 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 orbital 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^[11][14] list was expanded to include later mission types:^[1]: 466 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,^[15] was incorporated into the J-type missions.^[1]: 466

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.^[16]

Seven of the missions involved extravehicular activity (EVA), spacewalks or moonwalks outside of the spacecraft. These were of three types: testing the lunar EVA suit in Earth orbit (Apollo 9), exploring the lunar surface, and retrieving film canisters from the Scientific Instrument Module stored in the Service Module.^[17]

Mission	Patch	Launch date	Crew	Launch vehicle[b]	CM name	LM name	Duration	Remarks	Refs
Apollo 1		February 21, 1967 Launch Complex 34 (planned)	Gus Grissom Ed White Roger B. Chaffee	Saturn IB (SA-204)	—	—	—	Never launched. On January 27, 1967, a fire in the command module during a launch pad test killed the crew and destroyed the module. This flight was originally designated AS-204, and was renamed to Apollo 1 at the request of the crew's families.	[1][8][18][19][20]
Apollo 7		October 11, 1968 15:02 GMT Launch Complex 34	Wally Schirra Donn F. Eisele Walter Cunningham	Saturn IB (AS-205)	—	—	10 d 20 h 09 m 03 s	Test flight of Block II CSM in Earth orbit; included first live TV broadcast from American spacecraft.	[1][8][21][22][23]
Apollo 8		December 21, 1968 12:51 GMT Launch Complex 39A	Frank Borman James Lovell William Anders	Saturn V (SA-503)	—	—	06 d 03 h 00 m 42 s	First circumlunar flight of CSM, had ten lunar orbits in 20 hours. First crewed flight of Saturn V.	[1][8][24][25][26]
Apollo 9		March 3, 1969 16:00 GMT Launch Complex 39A	James McDivitt David Scott Rusty Schweickart	Saturn V (SA-504)	Gumdrop	Spider	10 d 01 h 00 m 54 s	First crewed flight test of Lunar Module; tested propulsion, rendezvous and docking in Earth orbit. EVA tested the Portable Life Support System (PLSS).	[1][8][27][28][29]
Apollo 10		May 18, 1969 16:49 GMT Launch Complex 39B	Thomas P. Stafford John Young Eugene Cernan	Saturn V (SA-505)	Charlie Brown	Snoopy	08 d 00 h 03 m 23 s	"Dress rehearsal" for lunar landing. The LM descended to 8.4 nautical miles (15.6 km) from lunar surface.	[1][8][30][31][32]
Apollo 11		July 16, 1969 13:32 GMT Launch Complex 39A	Neil Armstrong Michael Collins Edwin "Buzz" Aldrin	Saturn V (SA-506)	Columbia	Eagle	08 d 03 h 18 m 35 s	First crewed landing in Sea of Tranquility (Tranquility Base) including a single surface EVA.	[1][8][3][33]
Apollo 12		November 14, 1969 16:22 GMT Launch Complex 39A	Charles (Pete) Conrad Richard F. Gordon Jr. Alan Bean	Saturn V (SA-507)	Yankee Clipper	Intrepid	10 d 04 h 36 m 24 s	First precise Moon landing in Ocean of Storms near Surveyor 3 probe. Two surface EVAs and returned parts of Surveyor to Earth.	[1][8][34][35]
Apollo 13		April 11, 1970 19:13 GMT Launch Complex 39A	James Lovell Jack Swigert Fred Haise	Saturn V (SA-508)	Odyssey	Aquarius	05 d 22 h 54 m 41 s	Intended Fra Mauro landing cancelled after SM oxygen tank exploded. LM used as "lifeboat" for safe crew return. First S-IVB stage impact on Moon for active seismic test.	[1][8][36][7]
Apollo 14		January 31, 1971 21:03 GMT Launch Complex 39A	Alan Shepard Stuart Roosa Edgar Mitchell	Saturn V (SA-509)	Kitty Hawk	Antares	09 d 00 h 01 m 58 s	Successful Fra Mauro landing. Broadcast first color TV images from lunar surface (other than a few moments at the start of the Apollo 12 moonwalk.) Conducted first materials science experiments in space. Conducted two surface EVAs.	[1][8][37][38]
Apollo 15		July 26, 1971 13:34 GMT Launch Complex 39A	David Scott Alfred Worden James Irwin	Saturn V (SA-510)	Endeavour	Falcon	12 d 07 h 11 m 53 s	Landing at Hadley–Apennine. First extended LM, three-day lunar stay. First use of Lunar Roving Vehicle. Conducted three lunar surface EVAs and one deep space EVA on return to retrieve orbital camera film from SM.	[1][8][39][40]
Apollo 16		April 16, 1972 17:54 GMT Launch Complex 39A	John Young Ken Mattingly Charles Duke	Saturn V (SA-511)	Casper	Orion	11 d 01 h 51 m 05 s	Landing in Descartes Highlands. Conducted three lunar EVAs and one deep space EVA.	[1][8][41][42]
Apollo 17		December 7, 1972 05:33 GMT Launch Complex 39A	Eugene Cernan Ronald Evans Harrison Schmitt	Saturn V (SA-512)	America	Challenger	12d 13 h 51 m 59 s	Landing at Taurus–Littrow. First professional geologist on the Moon. First night launch. Conducted three lunar EVAs and one deep space EVA.	[1][8][9][43]

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,^[44] but waning public interest in the program led to decreased Congressional funding, forcing NASA to economize. First, Apollo 20 was cut to make a Saturn V available to launch the Skylab space station whole instead of building it on-orbit using multiple Saturn IB launches.^[45] 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.^[46][47]