What Apollo was
Apollo was a United States space program, run by NASA, with the goal of landing people on the Moon and bringing them safely home. President John F. Kennedy set that goal publicly in 1961, during the Cold War space race. Two earlier programs prepared the way: Mercury, which put the first Americans in space, and Gemini, which tested techniques such as docking two spacecraft and working outside in a spacesuit.
Apollo involved a huge workforce. Many thousands of engineers, technicians and contractors across the country worked on rockets, spacecraft, computers and training. The program was also costly, which was debated at the time.
The hardware
The Saturn V rocket launched the missions. It was about 110 meters tall and remains one of the most powerful rockets ever flown successfully. It used three stages, with each stage dropped when its fuel ran out, as described in our look at how a rocket reaches orbit.
The spacecraft had three main parts.
- The Command Module was the cone-shaped capsule where the three astronauts lived on the way to the Moon and the only part that returned to Earth.
- The Service Module held engines, power and supplies.
- The Lunar Module was a separate two-stage lander that carried two astronauts down to the surface. Its upper part lifted off from the Moon using the lower part as a launch platform, and then rejoined the Command Module in lunar orbit.
This method, called lunar orbit rendezvous, was chosen because it meant the heavy return vehicle did not need to land on the Moon.
Key milestones
- Apollo 1 (1967). A fire during a ground test killed astronauts Gus Grissom, Ed White and Roger Chaffee. The spacecraft was redesigned afterward.
- Apollo 8 (December 1968). The first crewed flight to orbit the Moon. It took the famous “Earthrise” photograph.
- Apollo 10 (May 1969). A full rehearsal in lunar orbit, without landing.
- Apollo 11 (July 1969). Neil Armstrong and Buzz Aldrin landed in the Sea of Tranquility on July 20, while Michael Collins stayed in orbit. They spent roughly two hours outside.
- Apollo 12, 14, 15, 16 and 17. Five more landings, with longer stays, more exploration and a battery-powered lunar rover on the last three. Apollo 17 in December 1972 was the last crewed trip to the Moon so far.
- Apollo 13 (April 1970). An oxygen tank failed on the way to the Moon, and the landing was canceled. The crew used the Lunar Module as a lifeboat and returned safely.
In all, six missions landed, and twelve astronauts walked on the Moon.
What the astronauts did there
The crews set up scientific instruments, collected rocks and soil, took photographs and measured things like the Moon’s surface properties. Later missions had longer stays and drove rovers to reach sites farther from the lander. Apollo 17 included a geologist, Harrison Schmitt.
Across the program, the missions returned roughly 380 kilograms of lunar rock and soil. Studying these samples gave scientists basic knowledge about the Moon’s age and makeup. The rocks include material billions of years old, and they are compatible with the idea, still the leading explanation, that the Moon formed from debris after a giant collision early in Earth’s history. Details of that theory are still researched.
Why we know the landings happened
Some people claim the landings were faked. The mainstream scientific and historical conclusion is that they were real, supported by many independent lines of evidence.
- Rock and soil samples. The lunar samples have been studied by laboratories in many countries for decades. They show features that are very hard to reproduce on Earth, such as no signs of water-related alteration, a particular pattern of exposure to cosmic rays and tiny glassy beads formed by impacts. They also differ from Earth rocks in ways consistent with a different origin, and they were also confirmed to be the same kinds of material found in later meteorites known to be from the Moon.
- Retroreflectors. Astronauts left mirror arrays on the surface. Observatories around the world have bounced laser beams off them to measure the Earth-Moon distance, and this has continued for decades.
- Independent tracking. The missions were followed by radio stations in other countries, including the Soviet Union, a rival that had every reason to expose a hoax and did not.
- Orbital photographs. Later spacecraft from the United States, India, Japan and China have photographed the landing sites from lunar orbit. Images show the descent stages, equipment and even trails left by astronauts and rovers.
- Scale of participation. A conspiracy would need many thousands of people, across multiple countries and decades, to keep a secret perfectly.
- Photos and film. The large archive of film, photos and telemetry is detailed, and apparent oddities that critics point to, such as the lack of stars in photos or a flag that seems to wave, have ordinary explanations. Stars are not visible because exposures were set for the brightly lit surface, and the flag had a horizontal rod to hold it out; it moved when touched, with nothing to damp the motion in a vacuum.
Why people went
The immediate motive was political and strategic competition, as covered in our history of space exploration. But the program also pushed forward electronics, materials, navigation and project management. The built-in computer for navigation was an early example of a small digital computer used where reliability was essential, though claims about specific everyday products being “invented by Apollo” are often exaggerated.
Why no one has been back since
After Apollo 17, costs, changing priorities and public interest led to canceled missions. NASA shifted toward the Space Shuttle and space stations. Returning to the Moon is now being pursued again under the Artemis program, among other efforts, though schedules have repeatedly moved. Robotic spacecraft from several countries have also continued to visit.
A note on the astronauts’ risks
Apollo crews faced real dangers: launch accidents, engine failures, the vacuum of space and radiation. They were exposed to more radiation than people in low Earth orbit, but the trips were short and the doses were limited. The Van Allen belts, regions of charged particles around Earth, were crossed quickly because of the trajectory used. This is one claim often raised by skeptics, and the actual measured doses were modest for the short transit.