Base Fregat upper stage marked the start of the whole family of highly effective upper stages, which were produced and are produced on its base. Application on the Fregat upper stage of additional fuel tanks and jettisonable tanks unit (Fregat-MT and Fregat-SB) made it possible to significantly increase the mass of loaded fuel and thereby increase the efficiency of the upper stage.
The basis of the structural-layout scheme of the Fregat upper stage is a block of tanks built according to a monoblock carrier scheme. It has a torospheric configuration, consisting of six spherical containers welded together, separated by spherical bottoms. Four of them are oxidizer and fuel tanks, two tanks are compartments for on-board instruments and equipment (one of them is sealed).
One of the containers (sealed) contains a monoblock of the control system including satellite navigation equipment and ventilators of thermal control system, another one (not sealed) contains a small instrument compartment, service units, as well as high pressure spherical tanks of sustainer propulsion system and propulsion system of attitude control system (ACS).
|Initial mass with maximum fueling, kg||6235||7640||11680|
|Final mass, kg||945||1035||1080|
|Dimensions: height/diame ter, mm||1875/3440||1945/3800||2435/3875|
|Fuel components: oxidizer/fuel||nitrogen tetroxide / unsymmetrical dimethylhydrazine||nitrogen tetroxide / unsymmetrical dimethylhydrazine||nitrogen tetroxide / unsymmetrical dimethylhydrazine|
|Maximum operational fuel reserve/full fueling, kg||5235/5307||6550/6650||10140/10330|
|Sustainer propulsion system thrust: BT/MT mode, kgf.||2030±100/1420±150||2030±100/1420±150||2030±100/1420±15|
|Specific impulse: BT/MT mode, f||333,2/320||333,2/320||333,2/320|
|Maximum switch on number of sustainer engine||7||7||7|