 Two crews made stays aboard Salyut 4 (Soyuz 17 and Soyuz 18), including one of 63 days duration.An uncrewed Soyuz capsule (Soyuz 20) remained docked to the station for three months, proving the system's long-term durability.Salyut 4 was deorbited on 2 February 1977, and re-entered the Earth's atmosphere the next day.