The RS-27A is a liquid-fuel rocket engine developed by Rocketdyne for use on the first stage of the Delta II and Delta III launch vehicles. It provides 1.05 meganewtons of thrust burning RP-1 and LOX in a gas-generator cycle. The engine is a modified version of its predecessor, the RS-27; its thrust nozzle has been extended to increase its area ratio from 8:1 to 12:1, which provides greater efficiency at altitude. The earlier RS-27 was derived from surplus H-1 engines used in the Saturn 1B launcher.
The RS-27A main engine is neither restartable nor throttleable. In addition to its main engine, the RS-27A includes two vernier engines to provide vehicle roll control during flight. The RS-27A has a run duration of 265 seconds.
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