The Salyut Program

The Salyut program (Russian: Салют; lit. Salute or Fireworks) was the first space station program undertaken by the Soviet Union, which consisted of a series of nine single-module space stations launched over a period of eleven years from 1971 to 1982. Intended as a project to carry out long-term research into the problems of living in space and a variety of astronomical, biological and Earth-resources experiments, the program allowed space station technology to evolve from the engineering development stage to long-term research outposts in space. Ultimately, experience gained from the Salyut stations went on to pave the way for multimodular space stations such as Mir and the International Space Station, with each of those stations possessing a Salyut-derived core module at its heart.
The program consisted of a series of six scientific research stations (DOS-type) and three military reconnaissance stations (OPS-type) launched as part of the highly secretive Almaz program, and during its development saw a number of spaceflight records broken, including several mission duration records, the first ever orbital handover of a space station from one crew to another and various spacewalk records. By the time the program concluded in 1991, it had seen space station technology evolve from basic, single-docking port stations to complex, multi-ported orbital outposts with impressive scientific capabilities, whose technological legacy continues to the present day.