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J-2 (rocket engine)

*** Shopping-Tip: J-2 (rocket engine)
The J-2 was America's largest liquid hydrogen fueled rocket engine before the Space Shuttle main engines were created (SSME). Five J-2 engines were used in the S-II second stage of the Saturn V rocket. One J-2 engine was used in the Saturn V third stage (S-IVB) and the Saturn IB second stage (S-IVB). There were proposals to use various numbers of J-2 engines in the upper stages of the planned Nova rocket. A unique characteristic of the J-2 engine was its ability to re-start after shutdown. The J-2 engine on the Saturn V third stage was intended to burn twice. The first burn, lasting for about two minutes, placed the Apollo spacecraft into earth orbit, and then shut down. After the crew members verified that the spacecraft was operating nominally, the J-2 was re-ignited for translunar injection. This 6.5 minute burn accelerated the Apollo spacecraft to escape velocity, and on a course for the moon.

The future of the J-2

A new variant of this engine (called the J-2X) has been designed to support the upcoming Project Constellation and its Crew Exploration Vehicle, which will replace the Space Shuttle upon its retirement in 2010. Originally the plan called for two J-2X engines to be used as the powerplant only for the CEV Earth Departure Stage|Earth Departure Stage, an uprated version of the Apollo S-IVB upper stage, but with need to get the CEV launched within a period of two years after the Shuttle's retirement, along with standardizing production, as well possible problems of testing an air-startable version of the Space Shuttle Main Engine, NASA announced that it will also use the new J-2X as the second-stage engine on its Crew Launch Vehicle.

Original J-2 specifications

Thrust (altitude): 200,000 lbf (890 kN)
Burn time: 500 s
Specific impulse: 418 s (4.1 kN·s/kg)
Engine weight - dry: 3,480 lb (1,578 kg)
Engine weight - burnout: 3,609 lb (1,637 kg)
Exit to Throat Area ratio: 27.5 to 1
Propellants: LOX & LH2
Mixture ratio: 5.00
Contractor: NAA/Rocketdyne
Vehicle Application: Saturn IB / S-IVB 2nd stage - 1-engine
Vehicle Application: Saturn V / S-II 2nd stage - 5-engines
Vehicle Application: Saturn V / S-IVB 3rd stage - 1-engine

Sources

Bilstein, R.E. (2003). Stages to Saturn. Gainesville: University of Florida Press.

External links

- Encyclopedia Astronautica link about the J-2

- Encyclopedia Astronautica link about the J-2S