The J-2X is a direct descendent of the J-2 rocket engine of Apollo fame. Intended specifically to be the upper stage engine for the ARES I, as well as the Earth Departure Stage engine for the ARES V, the J-2X will employ some of the design concepts of its forebear. But 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 rated for a design life of 8 starts and 2,600 seconds, and will be able to re-start in space in support of the lunar mission requirements. The engine will use a gas generator power cycle and burn liquid hydrogen and liquid oxygen, both sustained in cryogenic states.

At 15 feet, the J-2X will be four feet taller than its predecessor, will feature a nozzle made of a carbon composite and will weigh in at 5,450 pounds.

The first unmanned flight of the J-2X is set for 2013.