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.
Robbert Hutchings Goddard (1882–1945) is considered to be one of the fathers of modern rocket propulsion. A physicist of great insight, Goddard also had a unique genius for invention. By 1926, Goddard had constructed and tested successfully the first rocket using liquid fuel. Indeed, the flight of Goddard's rocket on March 16, 1926, at Auburn, Massachusetts, was a feat as epochal in history as that of the Wright brothers at Kitty Hawk. Yet, it was one of Goddard's "firsts" in the now booming significance of rocket propulsion in the fields of military missilery and the scientific exploration of space. Goddard's work largely anticipated in technical detail the later German V-2 missiles, including gyroscopic control, steering by means of vanes in the jet stream of the rocket motor, gimbal steering, power-driven fuel pumps and other devices. His rocket flight in 1929 carried the first scientific payload, a barometer, and a camera. Goddard developed and demonstrated the basic idea of the "bazooka" two days before the Armistice in 1918 at the Aberdeen Proving Ground. Goddard was the first scientist who not only realized the potentialities of missiles and spaceflight but also contributed directly in bringing them to practical realization. This rare talent in both creative science and practical engineering places Goddard well above the opposite numbers among the European rocket pioneers.