"I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth."

-President John F. Kennedy, 1961

On October 4, 1957, the Soviet Union’s satellite Sputnik I orbited the Earth. It was the world's first artificial satellite. On November 3, 1957, the Soviets launched Sputnik II. Included in the payload was a dog named Laika, the first living being sent into space. Initial American attempts to catch up to the Soviet Union’s advances in space ended in failure, inciting widespread public agitation that the United States was falling behind in this new, crucial arena of Cold War competition. But the goal of this competition remained unclear. Before a watchful world, each side sought to demonstrate its superiority through impressive feats in rocketry and spaceflight. Not until 1961, when President John F. Kennedy called for a lunar journey by the end of the decade did landing humans on the Moon become the focus of the space race. 

President Kennedy's decision to land men on the Moon before 1970 required the quickest, most efficient method possible. Three landing schemes were proposed. 

Direct

Direct (or 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 was already in development. 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 two rockets and assembling them in Earth orbit. Alternately, the whole spacecraft could be launched to Earth orbit, then a second tanker vehicle would refuel the last stage of the lunar spacecraft’s launch vehicle. The rest of the trip would be the same as Direct—with one spacecraft landing directly on the one and part of it returning to Earth.

Lunar Orbit Rendezvous (LOR)

LOR required two spacecraft sent up on a single launch vehicle. Over the course of a lunar journey, each craft performed a specific part of the mission. After reaching lunar orbit, the lander separated from the main spacecraft and descended to the surface. After performing its function on the surface, the cabin of the lander would lift off for rendezvous with the orbiting mothership, after which the astronauts would return to Earth in the main spacecraft. 

NASA 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. Most importantly, this decision propelled the United States forward in the Space Race, and on July 20th, 1969, President Kennedy's call to land a person on the Moon was successfully met.