Salyut 6 (Russian: Салют-6; lit. Salute 6) was a Sovietorbital space station, the eighth flown as part of the Salyut programme. Launched on 29 September 1977 by a Proton rocket, the station was the first of the 'second-generation' type of space station. Salyut 6 possessed several revolutionary advances over the earlier Soviet space stations, which it nevertheless resembled in overall design. These included the addition of a second docking port, a new main propulsion system and the station's primary scientific instrument, the BST-1M multispectral telescope. The addition of the second docking port made crew handovers and station resupply by unmanned Progress freighters possible for the first time, which in turn allowed the programme to evolve from short-duration station visits to long-duration expeditions, marking the beginning of the transition to multi-modular, long-term research stations in space.
From 1977 until 1982, Salyut 6 was visited by five long- and eleven short-duration crews, including cosmonauts from Warsaw Pact countries as part of the Intercosmos programme. The very first long-duration crew to visit the station broke a long-standing endurance record set on board the American Skylab station, staying 96 days in orbit; the longest expedition lasted 185 days. These crews were responsible for carrying out the primary missions of Salyut 6, including astronomy, Earth-resources observations and the study of human adaptation to space. Following the completion of these missions and the launch of its successor, Salyut 6 was deorbited on 29 July 1982, almost five years after its launch.
O'Neill began researching high-energy particle physics at Princeton in 1954 after he received his doctorate from Cornell University. Two years later, he published his theory for a particle storage ring. This invention allowed particle physics experiments at much higher energies than had previously been possible. In 1965 at Stanford University, he performed the first colliding beam physics experiment.
While teaching physics at Princeton, O'Neill became interested in the possibility that humans could live in outer space. He researched and proposed a futuristic idea for human settlement in space, the O'Neill cylinder, in "The Colonization of Space", his first paper on the subject. He held a conference on space manufacturing at Princeton in 1975. Many who became post-Apollo-era space activists attended. O'Neill built his first mass driver prototype with professor Henry Kolm in 1976. He considered mass drivers critical for extracting the mineral resources of the Moon and asteroids. His award-winning book The High Frontier: Human Colonies in Space inspired a generation of space exploration advocates. He died of leukemia in 1992.