Soyuz 20 was an unmanned spacecraft launched by the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

. It was a long-duration test of the Soyuz spacecraft

Soyuz spacecraft

Soyuz , Union) is a series of spacecraft initially designed for the Soviet space programme by the Korolyov Design Bureau in the 1960s, and still in service today...

 that docked with the Salyut 4

Salyut 4

Salyut 4 was a Salyut space station launched on December 26, 1974 into an orbit with an apogee of 355 km, a perigee of 343 km and an orbital inclination of 51.6 degrees. It was essentially a copy of the DOS 3, and unlike its ill-fated sibling it was a complete success...

 space station

Space station

A space station is a spacecraft capable of supporting a crew which is designed to remain in space for an extended period of time, and to which other spacecraft can dock. A space station is distinguished from other spacecraft used for human spaceflight by its lack of major propulsion or landing...

. 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 recovered on February 16, 1976.

Mission parameters

• Mass: 6570 kg (14,484.4 lb)
• Perigee: 177 km (110 mi)
• Apogee: 251 km (156 mi)
• Inclination: 51.6°
• Period: 89.1 minutes