Information AboutJ-2 (rocket Engine) |
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The J-2 was America's largest production Liquid Hydrogen fueled rocket engine before the Space Shuttle main engines ( SSME ). Five J-2 engines were used in the S-II , the second stage of the Saturn V rocket. One J-2 engine was used in S-IVB , which served as the third stage of the Saturn V, and the second stage of the Saturn IB . 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 J-2S An experimental program to improve the performance of the J-2 was started in 1964 as the J-2X. The main change to the original J-2 design was to change from the Gas Generator Cycle to a Tap-off Cycle which supplied the hot gas from a tap on the combusion chamber instead of a separate burner. In addition to removing parts from the engine, it also reduced the difficultly of starting up the engine and properly timing various combustors. Additional changes included a throttling system for wider mission flexibility, which also required a variable mixture system to properly mix the fuel and oxygen for a variety of different operating pressures. It also included a new "Idle Mode" which produced little thrust and could be used for on-orbit manuvering or to settle the fuel tanks on-orbit prior to a burn. During the experimental program, Rocketdyne also produced a small run of six pre-production models for testing, the J-2S. These were test fired many times between 1965 and 1972, for a total of 30,858 seconds burn time. In 1972 it became clear that follow-on orders for further Saturn boosters would not be forthcoming, and the program was shut down. NASA did consider using the J-2S on a number of different missions, and for some time a set of five were to power the Space Shuttle , a configuration that can be seen on early diagrams. THE FUTURE OF THE J-2 A new variant of this engine, confusingly 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 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 |