Salyut 4

Salyut 4 (DOS 4) (Russian: Салют-4, lit. 'Salute 4') was a Salyut space station launched on December 26, 1974, into an orbit with an apogee of 355 km (221 mi), a perigee of 343 km (213 mi) and an orbital inclination of 51.6 degrees. It was essentially a copy of the DOS 3 (or Kosmos 557), and, unlike its ill-fated sibling, it was a complete success. Three crews attempted to make stays aboard Salyut 4 (Soyuz 17 and Soyuz 18 docked; Soyuz 18a suffered a launch abort). The second stay was for 63 days duration, and an uncrewed capsule, called Soyuz 20, remained docked to the station for three months, proving the system's long-term durability despite some deterioration of the environmental system during Soyuz 18's mission. Salyut 4 was deorbited February 2, 1977, and re-entered the Earth's atmosphere on February 3. Salyut 4 represented the second phase of DOS civilian space station. Although the basic design of Salyut 1 was retained, it switched to three large solar panels mounted on the forward module rather than its predecessor's four small panels on the docking module and engine compartment, presumably to generate more power. It had an interior floor area of 34.8 m (375 sq ft) The thrusts of the station's attitude control thrusters were 2 X 59 N (pitch), 2 X 59 N (yaw) and 2 X 20 N (roll). The electric System produced an average of 2.00 kW of power. It had 2,000 kg (4,400 lb) of scientific equipment alongside two sets of three solar panels each and was equipped with the Delta Navigation System which was a new autonomous navigation system that calculates orbital elements without assistance from ground.