S1.5400

First staged combustion rocket engine ever developed, for the Soviet space program

The S1.5400 was a Soviet single-nozzle liquid-propellant rocket engine burning liquid oxygen and kerosene in an oxidizer-rich staged combustion cycle, being the first rocket engine to use this cycle in the world. It was designed by V. M. Melnikov, an alumnus of Isaev, within Korolev's Bureau, for the Molniya fourth stage, the Block-L. It was also the first Soviet engine designed for start and restart in vacuum and had the highest Isp at the time of its deployment.

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