Core vehicle of the OS was launched on February 20, 1986 from the launching pad Baikonur by the launch vehicle Proton-K. It is the central binding element of the complex. The mass of the vehicle at launch was equal to 21000 kg; fuel mass- 1200kg. It has two main solar batteries' panels with area equal to 2*38 m² (capacity -9 kW) and additional panel fixed by the cosmonauts. Total capacity of the solar batteries is 10.1 kW. Module has 6 docking ports (2 axial and 4 outlying) to dock the transportation ships and additional modules. The SPC Energy on the basis of the OS DOS (Salyut-7) developed it. At the launch mainly service systems were on the core vehicle. It is partly equipped by the scientific equipment from the OS Salyut-7 and by the equipment delivered by the CS Progress in the process of the exploitation of the complex.