Encyclopedia Astronautica

Fregat stage
Fregat upper stage for Soyuz launch vehicle.
Credit: Starsem
N2O4/UDMH propellant rocket stage. Loaded/empty mass 6,535/1,100 kg. Thrust 19.60 kN. Vacuum specific impulse 327 seconds. Upper stage developed from propulsion bus for Lavochkin lunar and planetary probes (Luna Ye-8, Mars M1, Fobos 1F). 20 restarts.

Status: In production.
Gross mass: 6,535 kg (14,407 lb).
Unfuelled mass: 1,100 kg (2,400 lb).
Height: 1.50 m (4.90 ft).
Diameter: 3.35 m (10.99 ft).
Span: 3.35 m (10.99 ft).
Thrust: 19.60 kN (4,406 lbf).
Specific impulse: 327 s.
Burn time: 877 s.

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Associated Countries
Associated Engines
  • S5.92 Isayev N2O4/UDMH rocket engine. 19.6 kN. Phobos propulsion module, later adapted as Fregat upper stage. In production. Isp=327s. Gas generator cycle. Nominal and low-thrust thrust levels. More...

Associated Launch Vehicles
  • Soyuz 11A511U / Fregat Russian orbital launch vehicle. Standard Soyuz universal booster with the Fregat upper stage, derived from the propulsion system for Lavochkin interplanetary probes. More...
  • Soyuz ST / Fregat ST Uprated Soyuz booster designed for commercial customers. Upgraded engines, modern avionics, reduced non-Russian content. Uses Fregat upper stage. More...

Associated Propellants
  • N2O4/UDMH Nitrogen tetroxide became the storable liquid propellant of choice from the late 1950's. Unsymmetrical Dimethylhydrazine ((CH3)2NNH2) became the storable liquid fuel of choice by the mid-1950's. Development of UDMH in the Soviet Union began in 1949. It is used in virtually all storable liquid rocket engines except for some orbital manoeuvring engines in the United States, where MMH has been preferred due to a slightly higher density and performance. More...

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