Soyuz 20
(Salyut 4 - Unmanned)

Launch:
    Date: 17 November 1975
    Time: 14:37 UTC
Landing:
    Date: 16 February 1976
    Time: 03:24 UTC
Duration: 90 days, 12 hours, 47 minutes

This was a test of the Progress automatic transport system. It docked with the Salyut 4 station. Noticeable degradation of systems on board Soyuz 20 led to an orbital limitation on the Soyuz craft to about 90 days.