What is the reason for space stations?

Answer 1

A space station (or orbital station) is a spacecraft capable of supporting a crew which is designed to remain in space (most commonly in low Earth orbit) for an extended period of time, and to which other spacecraft can dock. A space station is distinguished from other spacecraft used for human spaceflight by its lack of major propulsion or landing facilities. Instead other vehicles transport people and cargo to and from the station. As of October 2011[update] two space stations are in orbit; the International Space Station, and China's Tiangong 1. Previous stations include the Almaz and Salyut series, Skylab and most recently Mir.

Space stations are used to study the effects of long-term space flight on the human body as well as to provide platforms for greater number and length of scientific studies than available on other space vehicles. All space stations have been designed with the intention of rotating multiple crews, with each crew member staying aboard the station for weeks or months, but rarely more than a year. Since the ill-fated flight of Soyuz 11 to Salyut 1, all manned spaceflight duration records have been set aboard space stations. The duration record for a single spaceflight is 437.7 days, set by Valeriy Polyakov aboard Mir from 1994 to 1995. As of 2011[update], three astronauts have completed single missions of over a year, all aboard Mir.

Space stations have been used for both military and civilian purposes. The last military-use space station was Salyut 5, which was used by the Almaz program of the Soviet Union in 1976 and 1977.