The early history of the space program was dominated by the ‘space race’ between the United States of America and the (former) Soviet Union (USSR). The launch of the Soviet satellite Sputnik in October 1957 sent shock waves through the American psyche. With the successful launch of Explorer 1 into Earth orbit by Wernher von Braun and his colleagues in January 1959, America entered the race and the battle was joined. Over the next several years, the United States seemed to be catching up to the Soviets as it orbited many satellites and prepared to send men into the unknown, but once again, the Soviets struck first, as Yuri Gagarin was launched into Earth orbit in April 1961. The new American president, John F. Kennedy, searched desperately for a field to challenge the Soviets successfully. After due consideration, Kennedy set a decade-long goal of landing a man on the Moon and returning him safely to Earth.

Important information was needed about the Moon in advance of human missions to assure a safe voyage and landing. We needed to learn how to control spacecraft at lunar distances, how to maintain an orbit around the Moon, and how to land and operate safely where we didn't know the surface conditions. Having these knowledge requirements ensured the need for precursor missions, missions that would not only blaze the trail for the people to follow, but would invariably advance our understanding of the Moon and its environment in major ways (Table 3).