Rocketdyne J-2

The J-2, commonly known as Rocketdyne J-2, was a <a href="/facts/Liquid-fuel_rocket/TAonrVDn">liquid-fuel</a> <a href="/facts/Cryogenic_rocket_engine/MCUrNQ51">cryogenic rocket engine</a> used on <a href="/facts/NASA/TIMCV0yV">NASA</a>'s <a href="/facts/Saturn_IB/gpHk3gcW">Saturn IB</a> and <a href="/facts/Saturn_V/WhpUEFJM">Saturn V</a> launch vehicles. Built in the <a href="/facts/United_States/P0sCdLe5">United States</a> by <a href="/facts/Rocketdyne/3sGkwgd8">Rocketdyne</a>, the J-2 burned <a href="/facts/Cryogenic_fuel/4RHxUvG8">cryogenic</a> <a href="/facts/Liquid_hydrogen/Vpk3Gb8P">liquid hydrogen</a> (LH2) and <a href="/facts/Liquid_oxygen/qnI0KDTb">liquid oxygen</a> (LOX) propellants, with each engine producing 1,033.1 kN (232,250 lbf) of <a href="/facts/Thrust/EM04CqV7">thrust</a> in vacuum. The engine's preliminary design dates back to recommendations of the 1959 <a href="/facts/Silverstein_Committee/0VJSMkPB">Silverstein Committee</a>. Rocketdyne won approval to develop the J-2 in June 1960 and the first flight, <a href="/facts/AS-201/ge8ERVuf">AS-201</a>, occurred on 26 February 1966. The J-2 underwent several minor upgrades over its operational history to improve the engine's performance, with two major upgrade programs, the <a href="/facts/De_Laval_nozzle/5LcDcs69">de Laval nozzle</a>-type J-2S and <a href="/facts/Aerospike_engine/Dzqz1MFA">aerospike</a>-type J-2T, which were cancelled after the conclusion of the <a href="/facts/Apollo_program/IC1Ek1Ao">Apollo program</a>.
The engine produced a <a href="/facts/Specific_impulse/JKGgw2I4">specific impulse</a> (Isp) of 421 seconds (4.13 km/s) in a vacuum (or 200 seconds (2.0 km/s) at sea level) and had a mass of approximately 1,788 kilograms (3,942 lb). Five J-2 engines were used on the Saturn V's <a href="/facts/S-II/bFAjuM1s">S-II</a> second stage, and one J-2 was used on the <a href="/facts/S-IVB/CaTRQF2a">S-IVB</a> upper stage used on both the Saturn IB and Saturn V. Proposals also existed to use various numbers of J-2 engines in the upper stages of an even larger rocket, the planned <a href="/facts/Nova_(rocket)/nuQwaITg">Nova</a>. The J-2 was America's largest production LH2-fuelled rocket engine before the <a href="/facts/RS-25/vGkj6Vxm">RS-25</a>. A modernized version of the engine, the <a href="/facts/J-2X/JoWwCTkg">J-2X</a>, was considered for use on the <a href="/facts/Earth_Departure_Stage/eH8tD9E7">Earth Departure Stage</a> of NASA's <a href="/facts/Space_Shuttle/7BoyetEv">Space Shuttle</a> replacement, the <a href="/facts/Space_Launch_System/DbGCgH1W">Space Launch System</a>.
Unlike most liquid-fueled rocket engines in service at the time, the J-2 was designed to be restarted once after shutdown when flown on the Saturn V <a href="/facts/S-IVB/CaTRQF2a">S-IVB</a> third stage. The first burn, lasting about two minutes, placed the Apollo spacecraft into a low Earth <a href="/facts/Parking_orbit/wAk1jTxe">parking orbit</a>. After the crew verified that the spacecraft was operating nominally, the J-2 was re-ignited for <a href="/facts/Translunar_injection/nc16VTrG">translunar injection</a>, a 6.5 minute burn which accelerated the vehicle to a course for the <a href="/facts/Moon/zKHqEMPb">Moon</a>.

Rocketdyne J-2 open-in-new

Rocketdyne J-2