Progress 4

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Progress 4A (Progress 4) was a Soviet uncrewed cargo mission to the Salyut 6 space station in 1978. It used the Progress 7K-TG design and was the fourth Progress visit to Salyut 6. It launched on 3 October 1978 from Baikonur aboard a Soyuz-U rocket and carried about 2,436 kilograms of supplies, including 1,230 kg of pressurized cargo, 705 kg of fuel, 50 kg of gases, and 420 kg of water. The spacecraft weighed about 7,020 kg when fully fueled (about 6,520 kg dry) and measured 7.48 meters long and 2.72 meters in diameter. Progress 4 docked with Salyut 6's aft docking port on 6 October 1978 at 01:00:15 UTC, remaining attached for roughly 18.5 days. It undocked on 24 October and was deorbited on 26 October 1978 at 16:28 UTC, ending a 23-day mission. In its orbit, Progress 4 traveled in low Earth orbit with a perigee around 191 km, an apogee around 266 km, an inclination of 51.66 degrees, and an orbital period of about 88.8 minutes. The cargo supported scientific research on Salyut 6 and provided fuel for station maneuvers and orbit adjustments.