Apollo program

(PD) Photo: Astronaut Neil Armstrong, National Aeronautics and Space Administration
The first manned landing on the moon was successfully accomplished by the Apollo 11 mission on July 20, 1969. Astronaut Neil Armstrong took this photograph of fellow astronaut Edwin ("Buzz") Aldrin walking on the Moon's surface during lunar landing.

The Apollo program was a series of human spaceflight missions undertaken by the United States of America, during the years 1961–1974, using the Apollo spacecraft and Saturn space launch vehicle. It was conducted by the National Aeronautics and Space Administration (NASA) and was devoted to the goal, expressed in a 1961 address to the U.S. Congress by U.S. President John F. Kennedy, of "... landing a man on the Moon and returning him safely to the Earth ..." within the decade of the 1960s. That goal was successfully achieved by the Apollo 11 mission in July 1969.

The program continued until 1975 with five subsequent Apollo missions which also landed astronauts on the Moon, the last in December 1972. In the six successful Apollo spaceflights, twelve men walked on the Moon. As of 2011, these are the only times that humans have landed on another celestial body.

Equipment that was originally produced for the Apollo program was used for the later Skylab program during 1973–1974 and the joint U.S.−Soviet mission (Apollo−Soyuz Test Project) in 1975. Therefore, those subsequent programs are thus often considered to be part of the Apollo program.

Despite the many successes, there were two major failures, the first of which resulted in the deaths of three astronauts, Virgil "Gus" Grissom, Ed White and Roger Chaffee, in the Apollo 1 launchpad fire. The second was an explosion on Apollo 13, in whose aftermath the deaths of three more astronauts were averted by the efforts of flight controllers, project engineers, and backup crew members.

The Apollo program was named after the Greek god of the Sun.

Background

The Apollo program was originally conceived early in 1960, during the administration of President Eisenhower, 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 the Sun by NASA manager Abe Silverstein, who later said that "I was naming the spacecraft like I'd name my baby." 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.

(PD) Photo: Astronaut Neil Armstrong, National Aeronautics and Space Administration
The first landing on the Moon by a person from Earth accomplished by the Apollo 11 mission on July 20, 1969. Astronaut Neil Armstrong took this photograph of astronaut Edwin ("Buzz") Aldrin preparing to deploy a scientific experiment package unloaded from the Lunar Module.

In November 1960, John F. Kennedy was elected President after a campaign that promised American superiority over the Soviet Union in the fields of space exploration and missile defense. Using space exploration as a symbol of national prestige, he warned of a "missile gap" between the two nations, pledging to make the United States not "first but, first and, first if, but first period." Despite Kennedy's rhetoric, he did not immediately come to a decision on the status of the Apollo program once he was elected President. He knew little about the technical details of the space program, and was put off by the massive financial commitment required by a manned Moon landing. When NASA Administrator 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.

On April 12, 1961, Soviet cosmonaut Yuri Gagarin became the first man to fly in space, reinforcing American fears about being left behind in a technological competition with the Soviet Union. At a meeting of the U.S. House Committee on Science and Astronautics held only the day after Gagarin's flight, many congressmen pledged their support for a crash program aimed at ensuring that America would catch up. Kennedy, however, was circumspect in his response to the news, refusing to make a commitment on America's response to the Soviets. On April 20 Kennedy sent a memo to Vice President Lyndon B. Johnson, asking Johnson to look into the status of America's space program, and into programs that could offer NASA the opportunity to catch up. Johnson responded on the following day, concluding that "we are neither making maximum effort nor achieving results necessary if this country is to reach a position of leadership." 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.

On May 25, 1961, Kennedy announced his support for the Apollo program as part of a special address to a joint session of Congress:

"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."

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 disbelieved whether Kennedy's ambitious goal could be met.

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:

• 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: 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 descended 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.

Seamans' establishment of the Golovin committee in July 1961 represented a turning point in NASA's mission mode decision. 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. 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: "Without NASA's adoption of this stubbornly held minority opinion in 1962, the United States may still have reached the Moon, but almost certainly it would not have been accomplished by the end of the 1960s, President Kennedy's target date."

Spacecraft

(PD) Diagram: NASA
The Saturn V launch vehicle for the Apollo moon missions. The entire assembly weighed 2,900,000 kg (6,400,000 pounds) and was 110 m (363 feet) long at liftoff. It consisted of 5 parts: 3 rocket stages, an instrument unit, and the Apollo spacecraft.

The Apollo spacecraft consisted of three main sections, plus two minor sections.

The Command Module (CM) was the part in which the astronauts spent most of their time, including launch and landing. It was 10.6 feet in height and 12.8 feet in diameter. It was the only part that returned to Earth after the mission. The Service Module (SM) housed the equipment needed by the astronauts, such as oxygen tanks, and the engine that would take the spacecraft into and out of lunar orbit. The combined Command and Service modules were called the CSM.

The Lunar Module (LM; also known as Lunar Excursion Module, or LEM), was the part of the spacecraft that actually landed on the Moon. It was comprised of a descent stage and an ascent stage, the former serving as a launch platform for the latter when the lunar exploration party blasted off for lunar orbit where they would dock with the CSM prior to returning to Earth. To learn lunar landing techniques, astronauts practiced in the Lunar Landing Research Vehicle (LLRV), a flying vehicle that simulated (by means of a special, additional jet engine) the reduced gravity that the Lunar Module would actually fly in. The LLRV was later replaced by the three Lunar Landing Training Vehicles (LLTV), which were the primary training vehicles used by the astronauts.

The Launch Escape Tower (LET) would carry the Command Module clear of the launch vehicle, should it explode during launch, and the Spacecraft Lunar Module Adapter (SLA) was used to connect the spacecraft to the Launch Vehicle. In addition, on Apollos 9–17, it housed and protected the Lunar Module and on the ASTP flight, it housed the docking adapter.

Apollo missions and astronauts

The Apollo program included a number of unmanned test missions and 11 manned missions. The 11 manned missions included two Earth-orbiting missions (Apollo 7 and Apollo 9), two lunar-orbiting missions (Apollo 8 and Apollo 10), six successful lunar-landing missions, and one mission which was aborted, performed a lunar swingby, and successfully returned to Earth on an emergency basis. During the six lunar landings, on an overall basis, 12 different men lived, walked and worked on the surface of the Moon for a combined total of about 12.5 days.

The distance to the Moon at the apogee of its orbit around Earth is 405,000 km (252,000 miles). At the perigee of its orbit around Earth, the distance is 363,000 km (226,000 miles). Each of the manned Apollo missions took about 3 days to reach the moon.

The various Apollo missions and the astronauts that crewed the manned missions are listed in the table below:

The Apollo missions and the astronauts that crewed the manned missions 

Mission Identifier	Launch date	Launch rocket	Crew	Brief Mission Description
AS-201(a)	Feb. 26, 1966	Saturn 1B	Unmanned	36-minute suborbital test
AS-203(a)	July 5, 1966	Saturn 1B	Unmanned	88-minute test at Earth orbital altitude
AS-202(a)	Aug. 25, 1966	Saturn 1B	Unmanned	93-minute test at Earth orbital altitude
AS-204(a) (Apollo 1)	None	Saturn 1B	Virgil Grissom, Edward White, Roger Chaffee	Fire destroyed the Command Module and killed the three crew members during a launch pad test.
Apollo 4	Nov. 9, 1967	Saturn V	Unmanned	8-hour-and-37-minute test in Earth orbit (approximately six orbits)
Apollo 5	Jan. 22, 1968	Saturn 1B	Unmanned	11-hour-and-10-minute test in Earth orbit (approximately eight orbits)
Apollo 6	Apr. 4, 1968	Saturn V	Unmanned	10-hour-and-22-minute test in Earth orbit (approximately seven orbits)
Apollo 7	Oct. 11, 1968	Saturn 1B	Walter Schirra, Donn Eisele, Walter Cunningham	163 orbits of the Earth during a successful, fully manned test of almost 11 days (longer than a journey to the Moon and back).
Apollo 8	Dec. 21, 1968	Saturn V	Frank Borman, Jim Lovell, William Anders	First journey to Moon and back. Orbited the Moon ten times over a 20-hour period. The crew members were the first humans to see the far side of the Moon.
Apollo 9	Mar. 3, 1969	Saturn V	James McDivitt, David Scott, Russell Schweickart	10 days in Earth orbit. Tested the separation of the Lunar Module from the Command Module as well as the rendezvous and return docking of the Lunar Module.
Apollo 10	May 18, 1969	Saturn V	Thomas Stafford, John Young, Eugene Cernan	Second Apollo mission to orbit the Moon. A rehearsal of the Apollo 11 mission, in which all operations except the actual lunar landing were performed. Lunar Module separated and descended to 10 km from surface of Moon but did not land.
Apollo 11	July 16, 1969	Saturn V	Neil Armstrong, Edwin Aldrin, Michael Collins	First manned landing on the Moon, by Armstrong and Aldrin in the Lunar Module. Armstrong was first man to step on Moon's surface, followed later by Aldrin. Lunar surface stay of 21.6 hours and 59.5 hours in lunar orbit. Lunar Module left in lunar orbit when Command Module returned to Earth. Total mission about 8 days.
Apollo 12	Nov. 14, 1969	Saturn V	Charles Conrad, Alan Bean, Richard Gordon	Second manned lunar landing, by Conrad and Bean in the Lunar Module. Lunar surface stay of 31 hours and 89 hours in lunar orbit. Before returning to Earth, the Lunar Module was intentionally jettisoned so as to impact on the Moon. Total mission was about 10 days.
Apollo 13	Apr. 11, 1970	Saturn V	Jim Lovell, Jack Swigert, Fred Haise	An oxygen tank rupture at about 55 hours and 322,000 km (200,000 miles) into third lunar landing mission required aborting the mission. Apollo 13 continued around the Moon and returned to Earth under extreme emergency conditions. The Lunar Module was retained until the last possible moment in order to provide consumables to the Command module. Apollo 13 was classed a "successful failure" because of experience in rescuing crew.
Apollo 14	Jan. 31, 1971	Saturn V	Alan Shepard, Stuart Roosa, Edgar Mitchell	Third lunar landing, by Shepard and Mitchell in the Lunar Module. Lunar surface stay of 34 hours including 9.3 hours of Moon walks and other activities by Shepard and Mitchell, using 2-wheel tool cart for first time. 67 hours in lunar orbit by Command Module. The Lunar Module was intentionally jettisoned so as to impact on the Moon. Total mission was about 9 days.
Apollo 15	July 26, 1971	Saturn V	David Scott, Alfred Worden, James Irwin	Fourth lunar landing, by Scott and Irwin in the Lunar Module. Lunar surface stay of 67 hours including 18.5 hours of Moon walks by Scott and Irwin. First use of the Lunar Rover, a battery-driven 4-wheel drive car, which traversed about 28 km (17.4 miles). 145 hours for 74 lunar orbits by Command Module. The Lunar Module was intentionally jettisoned so as to impact on the Moon. Total mission was about 12.3 days.
Apollo 16	Apr. 16, 1972	Saturn V	John Young, Ken Mattingly, Charles Duke	Fifth lunar landing, by Young and Duke in the Lunar Module. Lunar surface stay of 71 hours including 20.3 hours for Moon walks and other activities by Young and Duke. Second time that Lunar Rover was used and driven for a total of 26.7 km (16.6 miles). 125 hours spent in 64 lunar orbits by the Command Module. The Lunar Module was left in lunar orbit because a minor malfunction prevented jettisoning to impact on the Moon. Total mission was about 11 days.
Apollo 17	Dec. 7, 1972	Saturn V	Eugene Cernan, Ronald Evans, Harrison Schmitt	Sixth lunar landing, by Cernan and Schmitt (a professional geologist). Lunar surface stay of about 75 hours including 22 hours for Moon walks and other activities by Cernan and Schmitt. The Lunar Rover was used and driven for 35 km (21.8 miles). 148 hours spent in 75 lunar orbits by the Command Module. The Lunar Module was intentionally jettisoned so as to impact on the Moon. Total mission was about 12.6 days.
(a) The AS prefix is an abbreviation for "Apollo-Saturn", referring to the Saturn launch rockets.

Moon rocks

Lunar Mission Sample Returned Apollo 11 22 kg Apollo 12 34 kg Apollo 14 43 kg Apollo 15 77 kg Apollo 16 95 kg Apollo 17 111 kg

Some of the Apollo program lunar missions collected, and returned to Earth with, samples of rocks and other materials from the Moon. In total, 382 kg (842 pounds) were collected, much of which is now stored at the Lunar Receiving Laboratory in Houston.

In general the rocks collected from the Moon are extremely old compared to rocks found on Earth, as measured by radiometric dating techniques. They range in age from about 3.2 billion years old for the basaltic samples derived from the lunar mare, to about 4.6 billion years for samples derived from the highlands crust. As such, they represent samples from a very early period in the evolution of the Solar System that is largely missing from Earth. One important rock found during the Apollo program was the Genesis Rock, retrieved by astronauts James Irwin and David Scott during the Apollo 15 mission. This rock is composed almost exclusively of the mineral anorthosite, and is believed to be representative of the highland crust. A geochemical component called KREEP (an acronym for rocks with high abundances of potassium, rare earth elements, and phosphorus) was discovered that has no known terrestrial counterpart. Together, KREEP and the anorthositic samples have been used to infer that the outer portion of the Moon was once completely molten.

Almost all of the rocks show evidence of having been affected by impact processes. For instance, many samples appear to be pitted with micrometeoroid impact craters, something which is never seen on Earth due to its thick atmosphere. Additionally, many show signs of being subjected to high pressure shock waves that are generated during impact events. Some of the returned samples are of impact melt, referring to materials that are melted in the vicinity of an impact crater. Finally, all samples returned from the Moon are highly brecciated as a result of being subjected to multiple impact events.

Apollo Applications

In the speech which initiated Apollo, Kennedy declared that no other program would have as great a long-range effect on America's ambitions in outer space. Following the success of the Apollo program, both NASA and its major contractors investigated several post-lunar applications for the Apollo hardware. The "Apollo Extension Series", later called the "Apollo Applications Program", proposed up to thirty flights to Earth Orbit. Many of these would use the space that the lunar module took up in the Saturn rocket to carry scientific equipment.

One plan involved using the Saturn IB to take the Command/Service Module (CSM) to a variety of low-Earth orbits for missions lasting up to 45 days. Some missions would involve the docking of two CSMs, and transfer of supplies. The Saturn V would be necessary to take it to polar orbit, or Sun-synchronous orbit (neither of which has yet been achieved by any manned spacecraft), and even to the geosynchronous orbit of Syncom 3, a communications satellite not quite in geostationary orbit. This was the first functioning communications satellite at that now-common great distance from the Earth, and it was small enough to be carried through the hatch and taken back to Earth for study as to the effects of radiation on its electronic components in that environment over a period of years. A return to the Moon was also planned, this time to orbit for a longer time to map the surface with high-precision equipment. This mission would not include a landing.

Of all the plans, only two were implemented: the Skylab space station (May 1973 – February 1974), and the Apollo-Soyuz Test Project (July 1975). Skylab's fuselage was constructed from the second stage of a Saturn IB, and the station was equipped with the Apollo Telescope Mount, itself based on a lunar module. The station's three crews were ferried into orbit atop Saturn IBs, riding in CSMs; the station itself had been launched with a modified Saturn V. Skylab's last crew departed the station on February 8, 1974, whilst the station itself returned prematurely to Earth in 1979, by which time it had become the oldest operational Apollo component.

The Apollo-Soyuz Test Project involved a docking in Earth orbit between an unnamed CSM and a Soviet Soyuz spacecraft. The mission lasted from July 15 to July 24, 1975. Although the Soviet Union continued to operate the Soyuz and Salyut space vehicles, NASA's next manned mission would not be until STS-1 on April 12, 1981.

In 1964/5 Grumman, the primary contractor for the Apollo LM systems, attempted to interest the USAF and Navy in a military version of CSM/LM configuration. The LM would have been equipped with a manipulator arm and projectile weapons to intercept and disable enemy satellites. The proposal was never fully developed and was abandoned in 1967. In the same time period, Grumman proposed using an Apollo spacecraft to send a mission to land on a near-Earth asteroid. Only about half a dozen were known at the time, with close approaches occurring about every three or four years. NASA found the scheme too marginal to pursue.

(PD) Photo: NASA Johnson Space Center
The Blue Marble: Earth viewed from Apollo 17 on way to Moon. The photo extends from Mediterranean Sea to Antarctica's south polar ice cap. Note cloud cover over Southern Hemisphere. A large part of Africa is visible. The Arabian Peninsula is seen at northeast edge of Africa. The large island off Africa's east coast is the Malagasy Republic.

Legacy of the Apollo program

The Apollo program in general, and the Apollo 11 landing on the Moon in particular, should be viewed as a watershed in the history of the United States. It demonstrated both the technological and economic virtuosity of the United States and established technological preeminence over rival nations -- the primary goal of the program when first envisioned by President Kennedy in 1961.

It had been an enormous undertaking involving "20,000 companies and hundreds of thousands individuals", as well as costing about $25.5 billion (about $170 billion in 2005 dollars),Only the building of the Panama Canal rivaled the Apollo program's size as the largest non-military technological endeavor ever undertaken by the United States ... and only the Manhattan Project to build the atomic bomb in World War II was comparable in a wartime setting.

The Apollo program gave the people of the world a new view of the planet Earth. On their outward voyage to the Moon, the crew of Apollo 8 focused a television camera on Earth and for the first time humanity saw its home as a tiny, lovely, and fragile "blue marble" hanging in the blackness of space. The modern environmental movement was galvanized in part by this new perception of the planet and the need to protect it and the life that it supports.

The Apollo program resulted in stimulating many areas of technology. The flight computer design used in both the Lunar and Command Modules was, along with the Minuteman Missile System, the driving force behind early research into integrated circuits. The fuel cell developed for this program was the first practical fuel cell. Computer-controlled machining (CNC) was pioneered in fabricating Apollo structural components.