J-2X Engine

Evolved from the proven J-2 engine that took astronauts to the moon, Aerojet Rocketdyne’s J-2X engine is specifically designed to power heavy lift upper stage vehicles toward deep space destinations. Delivering 30 percent more thrust than the Apollo-era engine upon which it is based, the J-2X is the highest performing human-rated upper stage engine to be developed in nearly 40 years. Its modern design and construction utilize a half-century of successful human spaceflight experience to meet today’s mission needs.

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.

Quick Facts & Key Milestones

  • July 2011 – Initiated first engine test series
  • Feb 2012 – Initiated powerpack test series
  • Feb 2013 – Initiated second engine test series
  • Nov 2013 – Initiated third engine test series




Thrust (Nominal)

Specific Impulse (Nominal)


Fuel: Hydrogen
Oxidizer: Liquid Oxygen
Mixture Ratio (O/F): 5.5–4.5

Vacuum: 294,000 lbs.
Chamber Pressure: 1,380 psia

Vacuum: 448 sec.

Length: 185 in.
Diameter: 120 in.
Weight: 5,450 lb.
Area Ratio: 92