Crewed spaceflight in the context of "Moonbase"

The Constellation program (abbreviated CxP) was a crewed spaceflight program developed by NASA, the space agency of the United States, from 2005 to 2009. The major goals of the program, in which no crewed missions flew before its cancellation, were "completion of the International Space Station" and a "return to the Moon no later than 2020" with a crewed flight to the planet Mars as the ultimate goal. The program's logo reflected the three stages of the program: the Earth (ISS), the Moon, and finally Mars—while the Mars goal also found expression in the name given to the program's booster rockets: Ares (the Greek equivalent of the Roman god Mars). The technological aims of the program included the regaining of significant astronaut experience beyond low Earth orbit and the development of technologies necessary to enable sustained human presence on other planetary bodies.

Constellation began in response to the goals laid out in the Vision for Space Exploration under NASA Administrator Sean O'Keefe and President George W. Bush. O'Keefe's successor, Michael D. Griffin, ordered a complete review, termed the Exploration Systems Architecture Study, which reshaped how NASA would pursue the goals laid out in the Vision for Space Exploration, and its findings were formalized by the NASA Authorization Act of 2005. The Act directed NASA to "develop a sustained human presence on the Moon, including a robust precursor program to promote exploration, science, commerce and US preeminence in space, and as a stepping stone to future exploration of Mars and other destinations." Work began on this revised Constellation Program, to send astronauts first to the International Space Station, then to the Moon, and then to Mars and beyond.

Gemini 4 (officially Gemini IV) was the second crewed spaceflight in NASA's Project Gemini, occurring in June 1965. It was the tenth crewed American spaceflight (including two X-15 flights at altitudes exceeding 100 kilometers (62 mi; 54 nmi)). Astronauts James McDivitt and Ed White orbited the Earth 66 times in four days, making it the first US flight to approach the five-day flight of the Soviet Vostok 5. The highlight of the mission was the first space walk by an American, during which White floated free outside the spacecraft, tethered to it, for approximately 23 minutes.

The flight also included the first attempt to make a space rendezvous as McDivitt attempted to maneuver his craft close to the Titan II upper stage which launched it into orbit, but this was not successful.

Apollo 8 (December 21–27, 1968) was the first crewed spacecraft to leave Earth's gravitational sphere of influence, and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times without landing and then returned to Earth. The three astronauts—Frank Borman, Jim Lovell, and William Anders—were the first humans to see and photograph the far side of the Moon and an Earthrise.

Apollo 8 launched on December 21, 1968, and was the second crewed spaceflight mission flown in the United States Apollo space program (the first, Apollo 7, stayed in Earth orbit). Apollo 8 was the third flight and the first crewed launch of the Saturn V rocket. It was the first human spaceflight from the Kennedy Space Center, adjacent to Cape Kennedy Air Force Station in Florida.

Gemini 12 (officially Gemini XII) was a 1966 crewed spaceflight in NASA's Project Gemini. It was the 10th and final crewed Gemini flight (Gemini 1 and Gemini 2 were uncrewed missions), the 18th crewed American spaceflight, and the 26th spaceflight of all time, including X-15 flights over 100 kilometers (54 nmi). Commanded by Gemini VII veteran James A. Lovell, the flight featured three periods of extravehicular activity (EVA) by rookie Edwin "Buzz" Aldrin, lasting a total of 5 hours and 30 minutes. It also achieved the fifth rendezvous and fourth docking with an Agena target vehicle.

Gemini XII marked a successful conclusion of the Gemini program, achieving the last of its goals by successfully demonstrating that astronauts can effectively work outside of spacecraft. This was instrumental in paving the way for the Apollo program to achieve its goal of landing a man on the Moon by the end of the 1960s.