Cyclone-4 LV first stage sustainer engine provides second stage starting up to the first space speed in the upper air layers.

The RD-261 consists of 3 double-chambers blocks which are assembled on a single frame fixing to a completed unit. Each block has its own turbo pump set and produced on the scheme without afterburning of turbine operating body. Combustion products of main propellant components are used as a turbine operating body.


Technical characteristics Value
Propellant components NTO (N2O4) + UDMH ((CH3)2N2H2)
Combustor pressure, kgs/ 88,8
Specific propulsive burn at the sea level, s 268,5
Sea level thrust, kgs 251082
Vacuum specific propulsive burn, s 299,0
Vacuum thrust, kgs 279603
Propellant mixture ratio 2,65
Firing time, s 120