The Kvant spacecraft represented the first use of a new kind of Soviet space station module, designated 37K. An order authorising the beginning of development was issued on 17 September 1979. The basic 37K design consisted of a 4.2 m diameter pressurised cylinder with a docking port at the forward end. It was not equipped with its own propulsion system. The original authorisation was for a total of eight 37K's of various configurations: