Salyut Six (DOS-5) was the eighth station of the Salyut programme and the fifth of the Durable Orbital Station series of civilian space stations. It was launched on 29 September 1977 by a Proton rocket and was the first space station to receive crewed and un-crewed spacecraft for human habitation, crew transfer, international participation and resupply. This established precedents for station life and operations on the later Mir and the International Space Stations.

Salyut Six was the first "second generation" soviet space station with major improvements in capabilities and operation. It had a new propulsion system and two docking ports, allowing two craft to visit simultaneously. This feature made it possible for crews to be re-supplied and remain aboard for several months.

Six long-term resident crews were supported by ten short-term visiting crews who arrived in newer Soyuz craft and departed in older craft. This left the newer craft available to the resident crew as a return vehicle so that they could stay past the design life of a Soyuz craft. Short-term visiting crews routinely included international cosmonauts from Warsaw pact countries participating in the Soviet Union's Intercosmos programme. These cosmonauts were the first from countries other than the Soviet Union or the United States.

Salyut Six was re-supplied by twelve un-crewed Progress spacecraft starting with Progress 1, the first of the series. Also it saw the first operational use of the new Soyuz-T spacecraft.

From 1977 to 1981, the station was occupied by crews during six separate, discontinuous intervals. Between each of these intervals Salyut 6 was vacant, although it was visited by Soyuz T-1 and Kosmos 1267 on un-crewed test missions. Following the launch of Salyut Seven, Salyut Six was de-orbited and destroyed on 29 July 1982 after five years in orbit.

Reference: Wikipedia - Salyut 6

The primary research instrument on Salyut Six was the BST-1M multispectral telescope, which could carry out astronomical observations in the infrared, ultraviolet and submillimeter spectra. It used a 1.5 metre-diameter mirror, which was operated in cryogenic conditions at around -269 °C (4 K). The telescope could be operated only when the station was on the night side of the Earth. Its cover was closed for the rest of the time.

The second major instrument was the MKF-6M multispectral camera, which carried out Earth-resources observations. This camera captured an area of 165 by 220 kilometres with each image, down to a resolution of 20 meters. Each image was captured simultaneously in six bands in 1200-frame cassettes. These required regular replacement due to the fogging effects of radiation.

Salyut Six also featured a KATE-140 stereoscopic topographic mapping camera with a focal length of 140 millimetres. This captured images of 450 by 450 kilometers with a resolution of 50 meters in the visible and infrared spectra. It could be operated either remotely or by the resident crews.

Salyut Six was also equipped with 20 portholes for observations, two scientific airlocks to expose equipment to space or eject rubbish, and various pieces of apparatus to carry out biological experiments. Later on during the flight, a Progress spacecraft delivered an external telescope, the KRT-10 [ru] radio observatory, which incorporated a directional antenna and five radiometers. The antenna was deployed on the rear docking assembly, with the controller remaining inside the station, and was used for both astronomical and meteorological observations.