J-2 (rocket Engine)

J-2 (rocket Engine)

The J-2 was a liquid-fuel cryogenic rocket engine used on NASA's Saturn IB and Saturn V launch vehicles. Built in the United States of America by Rocketdyne, the J-2 burned cryogenic liquid hydrogen & liquid oxygen propellants, with each engine producing 1,033.1 kN (232,250 lb_f) of thrust in vacuum. Development of the engine began in the 1960s, with the first flight, AS-201, occurring 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 de Laval nozzle-type J-2S and aerospike-type J-2T, being cancelled after the conclusion of the Apollo program.

The engine produced a specific impulse (I_sp) of 421 seconds in a vacuum (or 200 seconds at sea level) and had a mass of approximately 3,942 pounds (1,788 kg). Five J-2 engines were used on the Saturn V's S-II second stage, and one J-2 was used on the S-IVB 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 Nova. The J-2 was America's largest production liquid hydrogen fuelled rocket engine before the RS-25 Space Shuttle Main Engine, and a modernised version of the engine, the J-2X, is intended for use on the Earth Departure Stage of NASA's Space Shuttle replacement, the Space Launch System.

Unlike most liquid-fuelled rocket engines in service at the time, the J-2 was designed to be re-started once after shutdown when flown on the Saturn V. The first burn, lasting about two minutes, placed the Apollo spacecraft into a low Earth parking orbit. After the crew verified that the spacecraft was operating nominally, the J-2 was re-ignited for translunar injection, a 6.5 minute burn which accelerated the vehicle to a course for the Moon.