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Phobos Grunt base section model.jpg
Model of the Fregat-SB, as configured for the Fobos-Grunt mission's sample return vehicle
Manufacturer NPO Lavochkin
Country of origin Russia
Used on Soyuz, Zenit
General Characteristics
Height 1.5 m (4 ft 11 in)[1]
Diameter 3.35 m (11.0 ft)
Mass 6,500 kg (14,300 lb)
Propellant mass 5,350 kg (11,790 lb)
Engine details
Engines 1 S5.92
Thrust 20 kN (2,000 kgf)
Specific impulse 327 seconds (3.21 km/s)
Burn time 1,350 seconds[1]
Fuel N2O4/UDMH

Fregat (Russian: Фрегат, frigate) is an upper stage developed by NPO Lavochkin in the 1990s, which is used in some Soyuz and Zenit rockets. Its liquid propellant engine uses UDMH and N2O4.


The stage can be restarted up to 25 times,[1] which has been used to place payloads such as the GIOVE-B satellite into their planned orbits.[2]


NPO Lavochkin has built many interplanetary probes, 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 ("SBB" or Сбрасываемый Блок Баков in Russian) which makes increased payload capability possible. The torus-shaped SBB weighs 360 kilograms (790 lb) and contains up to 3,050 kilograms (6,720 lb) of propellant. The total dry weight of the Fregat-SB (including SBB) is 1,410 kilograms (3,110 lb) and the maximum propellant carrying capacity is 10,150 kilograms (22,380 lb). [3]

Fregat-SB was launched for the first time on 20 January 2011, when it lifted the Elektro-L weather satellite into geosynchronous orbit.[4]


Like the Fregat-SB, the Fregat-M/Fregat-MT configurations have detachable tanks on an additional block assembly which could be jettisoned when their task was complete. Additionally, the Fregat-M/Fregat-MT tanks have ball-shaped additions on the tops of the tanks. These additions increase the load capability of the propellant from 5,350 kilograms (11,790 lb) to 6,640 kilograms (14,640 lb), without causing any other changes to the physical dimensions of the vehicle.[5]


  1. ^ a b c "Fregat space tug". RussianSpaceWeb. Retrieved 26 July 2014. 
  2. ^ "Starsem successfully launches second Europe navigation satellite". Arianespace. 2008-04-27. 
  3. ^ "L'étage supérieur Fregat-SB : descriptif technique (in French)". 2012-12-12. 
  4. ^ "Russia meteo satellite Electro-L successfully orbited". ITAR-TASS. 2011-01-21. 
  5. ^ "Fregat versitile rocket stage". 2012-08-26. 

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