Lunar orbit rendezvous

Lunar orbit rendezvous (LOR) is a process for landing humans on the Moon and returning them to Earth. It was utilized for the Apollo program missions in the 1960s and 1970s. In a LOR mission, a main spacecraft and a lunar lander travel to lunar orbit. The lunar lander then independently descends to the surface of the Moon, while the main spacecraft remains in lunar orbit. After completion of the mission there, the lander returns to lunar orbit to rendezvous and re-dock with the main spacecraft, then is discarded after transfer of crew and payload. Only the main spacecraft returns to Earth.^[1]

Lunar orbit rendezvous was first proposed in 1919 by Ukrainian engineer Yuri Kondratyuk,^[2] as the most economical way of sending a human on a round-trip journey to the Moon.^[3][4]

The most famous example involved Project Apollo's command and service module (CSM) and lunar module (LM), where they were both sent to a translunar flight in a single rocket stack. However, variants where the landers and main spacecraft travel separately, such as the lunar landing plans proposed for Shuttle-Derived Heavy Lift Launch Vehicle, Golden Spike and the 2029/2030 Chinese crewed effort, are also considered to be lunar orbit rendezvous.