The J-2X engine will power the second stage of the Ares 1 rocket which will ferry astronauts to the Space Station as well as the Moon.

The gas generator was built by Pratt & Whitney Rocketdyne and will drive the Ares I’s turbopumps. Prior to main engine ignition, the generator will burn some Ares I rocket fuel (liquid hydrogen and oxygen) to create a stream of hot gases. These gases will power turbomachinery which then pumps rocket fuel into the main combustion chamber. The goal is to make the Ares 1 engine and gas generator reusable.

If all goes well, the Ares 1 will start carrying the Orion crew capsule and as many as six astronauts and small payloads to the space station in 2015.

rocket engine