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 smaller 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.
Lunar orbit rendezvous was first proposed in 1919 by Ukrainian engineer Yuri Kondratyuk, as the most economical way of sending a human on a round-trip journey to the Moon.
Yuri Alexeyevich Gagarin (9 March 1934 – 27 March 1968) was a Soviet cosmonaut and the first human to orbit the earth. Yuri Gagarin joined the Soviet Air Force in 1955 and graduated with honors from the Soviet Air Force Academy in 1957. Soon afterward, he became a military fighter pilot. By 1959, he had been selected for cosmonaut training as part of the first group of USSR cosmonauts. Yuri Gagarin flew only one space mission. On April 12, 1961 he became the first human to orbit Earth. Gagarin's spacecraft, Vostok 1, circled Earth at a speed of 27,400 kilometers per hour. The flight lasted 108 minutes. At its highest point, Gagarin was about 200 miles (327 kilometers) above Earth. Once in orbit, Yuri Gagarin had no control over his spacecraft. Vostok's reentry was controlled by a computer program sending radio commands to the space capsule. Although the controls were locked, a key had been placed in a sealed envelope in case an emergency situation made it necessary for Gagarin to take control. As was planned, Cosmonaut Gagarin ejected after reentry into Earth's atmosphere at an altitude of 20,000 feet and landed by parachute. As pilot of the spaceship Vostok 1, he proved that man could endure the rigors of lift-off, re-entry, and weightlessness. As a result of his historic flight he became an international hero and legend. Colonel Gagarin died on March 27, 1968 when the MiG-15 airplane he was piloting crashed near Moscow. He was given a hero's funeral, his ashes interred in the Kremlin Wall. He is popularly known as “The Columbus of the Cosmos”.
A transit of Earth by the Moon, as photographed by the Deep Space Climate Observatory from the Sun-Earth L1Lagrangian point. This animation was compiled from a set of 60 frames—20 distinct images, each compiled from monochrome images taken in red, green and blue filters—taken over the course of five hours on July 16, 2015. Each monochrome frame was taken every 30 seconds. Due to the speed of the Moon's motion, this results in a slight green shift in some frames of the animation.