Soyuz 20 (, Union 20) was an unmanned spacecraft launched by the Soviet Union. It was a long-duration test of the Soyuz spacecraft that docked with the Salyut 4 space station. Soyuz 20 performed comprehensive checking of improved on-board systems of the spacecraft under various flight conditions. It also carried a biological payload. Living organisms were exposed to three months in space. Mission parameters Mass: Perigee: Apogee: Inclination: 51.6° Period: 88.8 minutes Return It was recovered on 16 February 1976 at 02:24 UTC. References Soyuz uncrewed test flights Spacecraft launched in 1975 Spacecraft which reentered in 1976 Spacecraft launched by Soyuz-U rockets