HG-3 (rocket engine)

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Country of origin United States
Designer MSFC/Rocketdyne
Manufacturer Rocketdyne
Application Upper stage engine
Associated L/V Saturn MLV
Saturn IB-B
Saturn V/4-260
Saturn INT-17
Predecessor J-2
Successor RS-25
Status Cancelled during development.
Liquid-fuel engine
Propellant Liquid oxygen / Liquid hydrogen
Thrust (vac.) 1,400.7 kN (314,900 lbf)
Thrust (SL) 869.6 kN (195,500 lbf)
Isp (vac.) 451 seconds (4.42 km/s)
Isp (SL) 280 seconds (2.7 km/s)
References [1][2]

The HG-3 was a liquid-fuel cryogenic rocket engine which was designed for use on the upper stages of Saturn rockets in the post-Apollo era.[1] Designed in the United States by Rocketdyne, the HG-3 was to have burned cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing 1,400.7 kN (315,000 lbf) of thrust during flight.[1] The engine was designed to produce a specific impulse (Isp) of 451 seconds in a vacuum, or 280 seconds at sea level.[1] Developed from Rocketdyne's J-2 engine used on the S-II and S-IVB stages, the engine was intended to replace the J-2 on the upgraded S-II-2 and S-IVB-2 stages intended for use on the Saturn MLV, Saturn IB-B and Saturn V/4-260 rockets, with a sea-level optimised version, the HG-3-SL, intended for use on the Saturn INT-17.[1][2] The engine was cancelled, however, during the post-Apollo drawdown when development of the more advanced Saturn rockets ceased, and never flew, although the engine was later used as the basis for the design of the RS-25 Space Shuttle main engine.[3]

See also[edit]


  1. ^ a b c d e Mark Wade (17 November 2011). "HG-3". Encyclopedia Astronautica. Retrieved 18 February 2012. 
  2. ^ a b Mark Wade (17 November 2011). "HG-3-SL". Encyclopedia Astronautica. Retrieved 18 February 2012. 
  3. ^ "MSFC Propulsion Center of Excellence is Built on Solid Foundation". NASA. 1995. Retrieved 13 December 2011.