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
Spacecraft call signs the three-man crews to name both craft for each of their missions, and these names were used as the call signs. A temporary exception to this was on the first Moon landing, Apollo 11: since the first Moon landing site was in the Sea of Tranquillity, the call sign "Tranquillity Base" was used while the LM was on the lunar surface. Before and after independent flight of the LM, the mission number was used as the call sign. The Apollo call signs were: For project Skylab, the practice returned to using the mission name as the spacecraft call sign, since