Tail of an Thor XLT Stage with the RS-27 A engine.jpg
RS-27A Engine on Delta II
Country of originUnited States
ManufacturerRocketdyne, Pratt & Whitney Rocketdyne
Liquid-fuel engine
PropellantLOX / RP-1
CycleGas Generator
Thrust (vac.)1,054.2 kN
Thrust (SL)890.1 kN (200,102 lbf)
Thrust-to-weight ratio102.47
Chamber pressure4.8MPa (700 psia)
Isp (vac.)302 seconds (2.96 km/s)
Isp (SL)255 seconds (2.50 km/s)
Burn time265 Sec
Length3.78 m (12.40 ft)
Diameter1.70 m (5.58 ft)
Dry weight1,147 kg (2,528 lb)
Used in
Delta 7000, first stage[1]

The RS-27A is a liquid-fuel rocket engine developed in 1980s 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, it includes two vernier engines to provide vehicle roll control during flight.[4][failed verification]. When used as the main booster propulsion system for the Delta II family of launch vehicles, has an operational duration of 265 seconds. The last RS-27A engine was used for the ICESat-2 launch on 15 September, 2018.


  1. ^ Astronautix: RS-27A Engine
  2. ^ Astronautix: RS-27 Engine
  3. ^ Astronautix: RS-27 Derivation on Delta
  4. ^ "RS-27A Engine". Aerojet Rocketdyne. Retrieved May 15, 2018.

External links

  • Aerojet Rocketdyne RS-27A Product Page
  • Pratt and Whitney RS-27A Brochure