Soyuz 20 Soyuz 20 Soyuz 20 (Russian: Союз 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. It was reentered on 16 February 1976.