J2

J2, J.II or J-2 may refer to:

Codes and classifications

, the Earth's second dynamic form factor in the Nodal precession

People and organizations

Rocketdyne J-2

The J-2 was a liquid-fuel cryogenic rocket engine used on NASA's Saturn IB and Saturn V launch vehicles. Built in the U.S. by Rocketdyne, the J-2 burned cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) propellants, with each engine producing 1,033.1 kN (232,250 lb_f) of thrust in vacuum. The engine's preliminary design dates back to recommendations of the 1959 Silverstein Committee. Rocketdyne won approval to develop the J-2 in June 1960 and the first flight, AS-201, 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 de Laval nozzle-type J-2S and aerospike-type J-2T, which were cancelled after the conclusion of the Apollo program.

The engine produced a specific impulse (I_sp) 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 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 LH2-fuelled rocket engine before the RS-25 Space Shuttle Main Engine. A modernized 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.

S/2003 J 2

S/2003 J 2 is a retrograde irregular satellite of Jupiter. The discovery, by a team of astronomers from the University of Hawaii led by Scott S. Sheppard and David C. Jewitt, was announced on March 4, 2003.As of 2015, it is Jupiter's outermost known moon.

S/2003 J 2 is about 2 km (1.2 mi) in diameter, and orbits Jupiter at an average distance of 29.54 gigametres (0.1975 AU) in 981.55 days, at an inclination of 154° to the ecliptic (152° to Jupiter's equator) and with an eccentricity of 0.4100.

It seems to belong to a group all of its own, with semi-major axis ~30 gigametres (0.20 AU) and inclination ~160°.

The limits of Jupiter's gravitational influence are defined by its Hill sphere, whose radius is 52 gigametres (0.35 AU). Retrograde moons with axes up to 67% of the Hill radius are believed to be stable. Consequently, it is possible that even more distant moons of Jupiter may be discovered.

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