Apollo–Soyuz Test Project made the Soviet Union's policy of détente official in his 1956 doctrine of peaceful coexistence at the 20th Congress of the Communist Party of the Soviet Union, the two nations seemed to be in perpetual conflict. Due to tense relations, space cooperation between the United States and the Soviet Union was unlikely in the early 1970s. On June 7, 1971, the USSR had launched the first piloted orbital space station, Salyut 1. Meanwhile, the United States had launched the Apollo 14 mission several months prior, the third spacecraft to land humans on the moon. Each side gave the other little
Moon by the Soviet Union's Luna 2, an unmanned spacecraft. The United States' NASA Apollo program achieved the only manned lunar missions to date, beginning with the first manned orbital mission by Apollo 8 in 1968, and six manned landings between 1969 and 1972, with the first being Apollo 11. These missions returned lunar rocks which have been used to develop a geological understanding of the Moon's origin, internal structure, and the Moon's later history. Since the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft. Both the Moon's natural prominence in the earthly sky and