Kvant-1 was originally intended to be launched and docked to Salyut 7, but delays forced it to be launched to Mir instead. Kvant-1 did not have any propulsion systems of its own and to reach Mir, Kvant-1 was mated with a Functional Service Module (FSM) – carrying propulsion and electrical systems – to act as a space tug. The FSM was derived from the TKS spacecraft, which would later form the basis for the Functional Cargo Block of the Kvant-2, Kristall, Spektr, and Priroda modules.