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Tail of an Thor XLT Stage with the RS-27 A engine.jpg
RS-27A Engine on Delta II
Country of origin United States
Date 1989
Designer Rocketdyne
Manufacturer Rocketdyne, Pratt & Whitney Rocketdyne
Application Booster
Predecessor RS-27
Status In use
Liquid-fuel engine
Propellant LOX / RP-1
Cycle Gas Generator
Chamber 1
Thrust (vac.) 1,054.2 kN
Thrust (SL) 890.1 kN (200,102 lbf)
Thrust-to-weight ratio 102.47
Chamber pressure 4.8MPa (700 psia)
Isp (vac.) 302 seconds (2.96 km/s)
Isp (SL) 255 seconds (2.50 km/s)
Burn time 265 Sec
Length 3.78 m (12.40 ft)
Diameter 1.70 m (5.58 ft)
Dry weight 1,147 kg (2,528 lb)
Used in
Delta 7000, first stage[1]

The RS-27A is a liquid-fuel rocket engine developed[when?] by Rocketdyne for use on the first stage of the Delta II and Delta III launch vehicles. It provides 1.05 meganewtons (240,000 lbf) of thrust burning RP-1 and LOX in a gas-generator cycle. The engine is a modified version of its predecessor, the RS-27;[2] 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 Rocketdyne H-1 engines used in the Saturn 1B launcher.[3]

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.[citation needed] The RS-27A has a run duration of 265 seconds.[clarification needed]


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