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Soyuz 31 was a 1978 Soviet manned space flight to the Salyut 6 space station. It was the seventh mission to and sixth successful docking at the orbiting facility. The Soyuz 31 crew were the second to visit the long duration Soyuz 29 resident crew.
Soyuz 31 carried Valery Bykovsky and Sigmund Jahn, the first German cosmonaut, into space. They swapped Soyuz craft with the long duration crew and returned to earth in Soyuz 29, the resident crew returned to earth in Soyuz 31.
Soyuz 31 was the third Interkosmos flight.