J-2X Engine

A direct descendent of the rocket engine that powered Apollo to the moon.


Designed specifically to power heavy lift launch vehicles into Earth orbit and then beyond Earth orbit, Aerojet Rocketdyne's J-2X engine will employ some of the design concepts of its forebearer. It will also use modern analyses, materials and processes that have been proven on today's engine systems for greater efficiencies and increased power.

Total thrust in vacuum will be 294,000 pounds, and specific impulse will be 448 seconds, both significant increases over the original J-2. Each expendable J-2X is capable of four operational starts for 2,000 seconds, and will be able to restart in space in support of missions beyond low-Earth orbit. The engine will use a gas generator power cycle and burn liquid hydrogen with liquid oxygen, both sustained in cryogenic states.

At 15 feet, the J-2X will be four-feet taller than its predecessor and will weigh in at 5,450 pounds.



Thrust (in vacuum)

Specific Impulse (in vacuum)


Fuel: Hydrogen
Oxidizer: Liquid Oxygen

Thrust (in vacuum): 294,000 lbs.

Specific Impulse (in vacuum): 448 sec.
Pressure-Combustion Chamber: 1,380 psia
Mixed Ration (O/F): 5.5–4.5
Nozzle Area Ration: 92 

Length: 185 in.
Diameter: 120 in.
Weight: 5,450 lb.