Salyut 4

Salyut 4 was launched on December 26, 1974 into a 51.6-degree low Earth orbit. NASA HEASARC describes the station's Filin X-ray telescope and notes that Salyut 4 reentered Earth's atmosphere on February 2, 1977. During Soyuz 18, Klimuk and Sevastyanov spent nearly 63 days aboard the station, continuing biomedical, Earth-observation, solar-observation, and station systems work.