NASM--Apollo to the Moon--Choosing a Way to the Moon

CHOOSING A WAY TO THE MOON
President Kennedy's decision to land men on the Moon before 1970 required the quickest, most efficient method possible. Three landing schemes, described below, were proposed.
Associate Administrator Robert Seamans and Administrator James Webb selected the Lunar Orbit Rendezvous option in June 1962 after consultation with agency managers.
This decision affected the basic design of the major vehicles of the moon journey: particularly, the Saturn V rocket and the lunar module.

DIRECT-ASCENT
Direct-ascent utilized a single launch vehicle and one craft to land on the Moon and later return to Earth. This mode required no docking maneuvers in space, but did require a larger rocket than the one then in development-the Saturn V. Such a rocket would have been extremely difficult to complete by 1970.

EARTH ORBIT RENDEZVOUS (EOR)
EOR required launching the lunar spacecraft in pieces aboard several rockets and assembling them in Earth orbit. Each piece served a particular function during the mission and would then be discarded.

LUNAR ORBIT RENDEZVOUS (LOR)
LOR required several craft, sent up on a single launch vehicle. Over the course of a lunar journey, each craft performed a specific part of the mission. After attaining lunar orbit, the lander separated from the main craft and descended to the surface. After performing its function on the surface, part of the lander lifted-off for rendezvous with the orbiting ship which returned to Earth, leaving the lander in lunar orbit.

PROBING THE MOON