Uses
NPO Lavochkin created many interplanetary probes in the past, and the Fregat stage follows their design traditions. The main part of the stage is six intersecting spheres placed on a single plane, four of which contain propellants. The remaining two contain the control equipment. The main engine is placed between the spheres, so Fregat is a tightly-packed stage with a diameter much larger than its height.
Fregat is a versatile spacecraft. For example, in addition to orbital insertion, it can be used as an escape stage to launch modern space probes into interplanetary trajectories (e.g., Venus Express and Mars Express).
Fregat stages are currently used as the fourth stage of some Soyuz-FG launch vehicles. A version called Fregat-SB can be used with Zenit-2SB rocket. This version has a block of drop-off tanks which makes increased payload capability possible. Fregat-SB was launched for the first time on 20 January 2011, when it lifted the Elektro-L weather satellite into geosynchronous orbit.
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