Apollo program in the context of Canceled Apollo missions

Spaceflight (or space flight) is an application of astronautics to fly objects, usually spacecraft, into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth, but also includes space probes for flights beyond Earth orbit. Such spaceflights operate either by telerobotic or autonomous control. The first spaceflights began in the 1950s with the launches of the Soviet Sputnik satellites and American Explorer and Vanguard missions. Human spaceflight programs include the Soyuz, Shenzhou, the past Apollo Moon landing and the Space Shuttle programs. Other current spaceflight are conducted to the International Space Station and to China's Tiangong Space Station.

Spaceflights include the launches of Earth observation and telecommunications satellites, interplanetary missions, the rendezvouses and dockings with space stations, and crewed spaceflights on scientific or tourist missions.

The National Aeronautics and Space Administration (NASA /ˈnæsə/) is an independent agency of the US federal government responsible for the United States' civil space program and for research in aeronautics and space exploration. Headquartered in Washington, D.C., NASA operates ten field centers across the United States and is organized into mission directorates for Science, Space Operations, Exploration Systems Development, Space Technology, Aeronautics Research, and Mission Support. Established in 1958, NASA succeeded the National Advisory Committee for Aeronautics (NACA) to give the American space development effort a distinct civilian orientation, emphasizing peaceful applications in space science. It has since led most of America's space exploration programs, including Project Mercury, Project Gemini, the 1968–1972 Apollo program missions, the Skylab space station, and the Space Shuttle.

The agency maintains major ground and communications infrastructure including the Deep Space Network and the Near Space Network. NASA's science division is focused on better understanding Earth through the Earth Observing System; advancing heliophysics through the efforts of the Science Mission Directorate's Heliophysics Research Program; exploring bodies throughout the Solar System with advanced robotic spacecraft such as New Horizons and planetary rovers such as Perseverance; and researching astrophysics topics, such as the Big Bang, through the James Webb Space Telescope, the four Great Observatories (including the Hubble Space Telescope), and associated programs. The Launch Services Program oversees launch operations for its uncrewed launches.

Victor Hasselblad AB is a Swedish manufacturer of medium format cameras, photographic equipment and image scanners based in Gothenburg, Sweden. The company originally became known for its classic analog medium-format cameras that used a waist-level viewfinder. Perhaps the most famous use of the Hasselblad camera was during the Apollo program missions when the first humans landed on the Moon. Almost all of the still photographs taken during these missions used modified Hasselblad cameras. In 2016, Hasselblad introduced the world's first digital compact mirrorless medium-format camera, the X1D-50c, changing the portability of medium-format photography. Hasselblad produces about 10,000 cameras a year from a small three-storey building.

The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized astronomical event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided into the terrestrial planets and their natural satellites in the inner Solar System, including Mercury, Venus, Earth (and the Moon) and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although it has gained widespread credence, definitive evidence remains elusive.

Evidence for the LHB derives from moon rock samples of Lunar craters brought back by the Apollo program astronauts. Isotopic dating showed that the rocks were last molten during impact events in a rather narrow interval of time, suggesting that a large proportion of craters were formed during this period. Several hypotheses attempt to explain this apparent spike in the flux of impactors in the inner Solar System, but no consensus yet exists. The Nice model, popular among planetary scientists, postulates that the giant planets underwent orbital migration, scattering objects from the asteroid belt, Kuiper belt, or both, into eccentric orbits and into the path of the terrestrial planets.

Human spaceflight (also referred to as crewed spaceflight, or more historically manned 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 remotely operated from ground stations on Earth, or autonomously, without any direct human involvement. People trained for spaceflight are called astronauts (American or other), cosmonauts (Russian), or taikonauts (Chinese); and non-professionals are referred to as spaceflight participants or spacefarers.

The first human in space was Soviet cosmonaut Yuri Gagarin, who launched as part of the Soviet Union's Vostok program on 12 April 1961 at the beginning of the Space Race. On 5 May 1961, Alan Shepard became the first American in space, as part of Project Mercury. Humans traveled to the Moon nine times between 1968 and 1972 as part of the United States' Apollo program, and have had a continuous presence in space for 25 years and 30 days on the International Space Station (ISS). On 15 October 2003, the first Chinese taikonaut, Yang Liwei, went to space as part of Shenzhou 5, the first Chinese human spaceflight. As of December 2025, humans have not traveled beyond low Earth orbit since the Apollo 17 lunar mission in December 1972.

Project Gemini (IPA: /ˈdʒɛmɪni/) was the second United States human spaceflight program to fly. It was conducted after the first American crewed space program, Project Mercury, while the Apollo program was still in early development. Gemini was conceived in 1961 and concluded in 1966. The Gemini spacecraft carried a two-astronaut crew. Ten Gemini crews and 16 individual astronauts flew low Earth orbit (LEO) missions during 1965 and 1966.

Gemini's objective was the development of space travel techniques to support the Apollo mission to land astronauts on the Moon. In doing so, it allowed the United States to catch up and overcome the lead in human spaceflight capability the Soviet Union had obtained in the early years of the Space Race, by demonstrating mission endurance up to just under 14 days, longer than the eight days required for a round trip to the Moon; methods of performing extravehicular activity (EVA) without tiring; and the orbital maneuvers necessary to achieve rendezvous and docking with another spacecraft. This left Apollo free to pursue its prime mission without spending time developing these techniques.

Apollo 11 was the first spaceflight to land humans on the Moon, conducted by NASA from July 16 to 24, 1969. Commander Neil Armstrong and Lunar Module Pilot Edwin "Buzz" Aldrin landed the Lunar Module Eagle on July 20 at 20:17 UTC, and Armstrong became the first person to step onto the surface about six hours later, at 02:56 UTC on July 21. Aldrin joined him 19 minutes afterward, and together they spent about two and a half hours exploring the site they had named Tranquility Base upon landing. They collected 47.5 pounds (21.5 kg) of lunar material to bring back to Earth before re-entering the Lunar Module. In total, they were on the Moon’s surface for 21 hours, 36 minutes before returning to the Command Module Columbia, which remained in lunar orbit, piloted by Michael Collins.

Apollo 11 was launched by a Saturn V rocket from Kennedy Space Center in Florida, on July 16 at 13:32 UTC (9:32 am EDT, local time). It was the fifth crewed mission of the Apollo program. The Apollo spacecraft consisted of three parts: the command module (CM), which housed the three astronauts and was the only part to return to Earth; the service module (SM), which provided propulsion, electrical power, oxygen, and water to the command module; and the Lunar Module (LM), which had two stages—a descent stage with a large engine and fuel tanks for landing on the Moon, and a lighter ascent stage containing a cabin for two astronauts and a small engine to return them to lunar orbit.

The physical exploration of the Moon began when Luna 2, a space probe launched by the Soviet Union, made a deliberate impact on the surface of the Moon on 14 September, 1959. Prior to that the only available means of lunar exploration had been observations from Earth. The invention of the optical telescope brought about the first leap in the quality of lunar observations. Galileo Galilei is generally credited as the first person to use a telescope for astronomical purposes, having made his own telescope in 1609. The mountains and craters on the lunar surface were among his first observations.

Human exploration of the Moon since Luna 2 has consisted of both crewed and uncrewed missions. NASA's Apollo program has been the only program to successfully land humans on the Moon, which it did six times on the near side in the late 20th century. The first human landing took place in 1969, when the Apollo 11 astronauts Buzz Aldrin and Neil Armstrong touched down on the surface in the region of Mare Tranquillitatis, leaving scientific instruments upon the mission's completion and returning lunar samples to Earth. All lunar missions had taken place on the lunar near side until the first soft landing on the far side of the Moon was made by the CNSA robotic spacecraft Chang'e 4 in early 2019, which successfully deployed the Yutu-2 robotic lunar rover. On 25 June 2024, CNSA's Chang'e 6 conducted the first lunar sample return from the far side of the Moon.

The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight in Houston, Texas (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight control are conducted. It was renamed in honor of the late U.S. president and Texas native, Lyndon B. Johnson, by an act of the United States Senate on February 19, 1973.

JSC consists of a complex of 100 buildings constructed on 1,620 acres (660 ha) in Clear Lake. The center is home to NASA's astronaut corps, and is responsible for training astronauts from both the U.S. and its international partners. It also houses the Christopher C. Kraft Jr. Mission Control Center, which has provided the flight control function for every NASA human spaceflight since Gemini 4 (including Apollo, Skylab, Apollo–Soyuz, and Space Shuttle). It is popularly known by its radio call signs "Mission Control" and "Houston".

Apollo 9 (March 3–13, 1969) was the third human spaceflight in NASA's Apollo program, which successfully tested systems and procedures critical to landing on the Moon. The three-man crew consisted of Commander James McDivitt, Command Module Pilot David Scott, and Lunar Module Pilot Rusty Schweickart. 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 full Apollo spacecraft: the command and service module (CSM) with the Lunar Module (LM).

The mission was flown to qualify the LM for lunar orbit operations in preparation for the first Moon landing by demonstrating its descent and ascent propulsion systems, showing that its crew could fly it independently, then rendezvous and dock with the CSM again, as would be required for the first crewed lunar landing. Other objectives of the flight included firing the LM descent engine to propel the spacecraft stack as a backup mode (as was required on the Apollo 13 mission), and use of the portable life support system backpack outside the LM cabin.

The magnetic field of the Moon is very weak in comparison to that of the Earth; the major difference is the Moon does not have a dipolar magnetic field currently (as would be generated by a geodynamo in its core), so that the magnetization present is varied (see picture) and its origin is almost entirely crustal in location; so it's difficult to compare as a percentage to Earth. But, one experiment discovered that lunar rocks formed 1 - 2.5 billion years ago were created in a field of about 5 microtesla (μT), compared to present day Earth's 50 μT. During the Apollo program several magnetic field strength readings were taken with readings ranging from a low of 6γ (6nT) at the Apollo 15 site to a maximum of 313γ (0.31μT) at the Apollo 16 site, note these readings were recorded in gammas(γ) a now outdated unit of magnetic flux density equivalent to 1nT.

One hypothesis holds that the crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. An analysis of magnetized Moon rocks brought to Earth by Apollo astronauts showed that the Moon must have had a strong (above 110 μT) magnetic field at least 4.25 billion years ago, which then fell to 20 μT level in the 3.6 - 3.1 billion years BP period. The small size of the lunar core, however, is a potential obstacle to promoting that hypothesis to the status of theory. However, single silicate grains with magnetic inclusions from Apollo rocks formed at 3.9, 3.6, 3.3, and 3.2 billion years ago have been shown to be capable of recording strong magnetic fields but do not. This supports the alternative hypothesis that the Moon never had a long-lasting core dynamo, consistent with the lack of energy needed to sustain a field.

The geology of the Moon (sometimes called selenology, although the latter term can refer more generally to "lunar science") is the structure and composition of the Moon, which is quite different from that of Earth. The Moon lacks a true atmosphere outside of a sparse layer of gas. Because of this, the absence of free oxygen and water eliminates erosion due to weather. Instead, the surface is eroded much more slowly through the bombardment of the lunar surface by micrometeorites. It does not have any known form of plate tectonics, along with having a lower gravity compared to Earth. Because of its small size, it cooled faster in the early days of its formation. In addition to impacts, the geomorphology of the lunar surface has been shaped by volcanism, which is now thought to have ended less than 50 million years ago. The Moon is a differentiated body, with a crust, mantle, and core.

Geological studies of the Moon are based on a combination of Earth-based telescope observations, measurements from orbiting spacecraft, lunar samples, and geophysical data. Six locations were sampled directly during the crewed Apollo program landings from 1969 to 1972, which returned 382 kilograms (842 lb) of lunar rock and lunar soil to Earth. In addition, three robotic Soviet Luna spacecraft returned another 301 grams (10.6 oz) of samples, and the Chinese robotic Chang'e 5 returned a sample of 1,731 g (61.1 oz) in 2020.

Apollo 10 (May 18–26, 1969) was the fourth human spaceflight in the United States' Apollo program and the second to orbit the Moon. NASA, the mission's operator, described it as a "dress rehearsal" for the first Moon landing (Apollo 11, two months later). It was designated an "F" mission, intended to test all spacecraft components and procedures short of actual descent and landing.

After the spacecraft reached lunar orbit, astronaut John Young remained in the Command and Service Module (CSM) while astronauts Thomas Stafford and Gene Cernan flew the Apollo Lunar Module (LM) to within 14.4 kilometers (7.8 nautical miles; 9 miles) of the lunar surface, the point at which powered descent for landing would begin on a landing mission. After four orbits they rejoined Young in the CSM and, after the CSM completed its 31st orbit of the Moon, they returned safely to Earth.

Apollo 17 (December 7–19, 1972) was the eleventh and final mission of NASA's Apollo program, the sixth and most recent time humans have set foot on the Moon. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on the Moon, while Command Module Pilot Ronald Evans orbited above. Schmitt was the only professional geologist to land on the Moon; he was selected in place of Joe Engle, as NASA had been under pressure to send a scientist to the Moon. The mission's heavy emphasis on science meant the inclusion of a number of new experiments, including a biological experiment containing five mice that was carried in the command module.

Mission planners had two primary goals in deciding on the landing site: to sample lunar highland material older than that at Mare Imbrium and to investigate the possibility of relatively recent volcanic activity. They therefore selected Taurus–Littrow, where formations that had been viewed and pictured from orbit were thought to be volcanic in nature. Since all three crew members had backed up previous Apollo lunar missions, they were familiar with the Apollo spacecraft and had more time for geology training.

Harrison Hagan "Jack" Schmitt (born July 3, 1935) is an American geologist, former NASA astronaut, university professor, and former U.S. senator from New Mexico. He is the most recent living person—and only person without a background in military aviation—to have walked on the Moon.

In December 1972, as a crewmember of Apollo 17, Schmitt became the first member of NASA's first scientist-astronaut group to fly in space. As Apollo 17 was the last of the Apollo missions, he also became the twelfth and second-youngest person to set foot on the Moon and the second-to-last person to step off of the Moon (he boarded the Lunar Module shortly before commander Eugene Cernan). Schmitt also remains the only professional scientist to have flown beyond low Earth orbit and to have visited the Moon. Before training for Apollo 17, he was influential in the geology field for supporting the Apollo program and had helped train Apollo astronauts chosen to visit the lunar surface.