Three minutes later, the protective payload fairing was jettisoned, unveiling the spacecraft and the Fregat-SB upper stage.[1]

The stage is made up of six overlapping spherical sections, only four of which serve as propellant tanks. Two remaining spheres are actually instrument sections, one containing unpressurized avionics, which can function in vacuum of space and another, pressurized, section holding a flight control computer, which requires a temperature-controlled environment.

At least four spherical gas tanks with a diameter of 375 millimeters and a capacity of 23 liters are carried onboard Fregat. [2]

[1] http://www.alternative-learning.org/nl/wordpress/?p=4082 [2] http://www.russianspaceweb.com/fregat.html