Kosmos 638 () was an uncrewed test of the 1975 Apollo–Soyuz Test Project Soyuz. It carried an APAS-75 androgynous docking system. This was followed by another uncrewed test of this spacecraft type, Kosmos 672. It was a Soyuz 7K-TM spacecraft. When the air was released from the orbital module (which is ejected before re-entry of the capsule) it caused unexpected motions with the spacecraft. This led to the next test also being uncrewed. Mission parameters Spacecraft: Soyuz-7K-TM №71 Mass: 6510 to 6680 kg Crew: None Launched: April 3, 1974 Landed: April 13, 1974 References Mir Hardware Heritage Mir Hardware Heritage (NASA report RP 1357) (PDF format) Mir Hardware Heritage (NASA report RP 1357) (Wikisource) Kosmos 0638 1974 in the Soviet Union Spacecraft launched in 1974 Apollo–Soyuz Test Project Soyuz uncrewed test flights