NASA will pay Pratt & Whitney Rocketdyne (PWR) a total of $1.2 billion through the end of 2012 to develop and deliver eight J2-X rocket engines for the U.S. aerospace agency's planned Ares family of launch vehicles.

Jeff Hanley, who heads NASA's Constellation Program that is building the vehicles necessary for a human return to the moon, said the schedule covered by the contract signed July 16 will support the current program target that sees the engine flying its first humans to space in September 2013.

Sole-source contracts for backup test hardware and production rocket engines will be negotiated later. The company, which built the original J-2 engine that powered the Saturn V upper stages during the Apollo program of the 1960s, has been working on the engine under a sole-source letter contract since June 2006. Funds spent under that arrangement are reflected in the final contract amount.

The J-2X is a 294,000-pound thrust version of the original engine, which generated 230,000 pounds of thrust. It will have a specific impulse of 448 seconds, weigh 5,450 pounds and stand 15 feet, five inches high. Exploration managers selected the engine to power the upper stage of the Ares I crew launch vehicle that will carry the Orion crew capsule, and eventually the Earth-departure stage of the Ares V heavy lifter, which will boost the Orion and a lunar surface access module into a cislunar trajectory.

Although it is based on the human-rated J-2 and its follow-on J2-S, which never flew, the J-2X will be extensively reworked to incorporate modern materials and manufacturing techniques. The combustion chamber, for example, will be built using hot isostatic pressure (HIP) bonding instead of the time-consuming hand lay-up of the 1960s, according to Mike Kynard, the J2-X project manager at Marshall Space Flight Center.

"We're making some changes to nearly all the parts," Kynard said during a telephone press conference announcing the final contract.

NASA is building a new test stand at Stennis Space Center in Mississippi to accommodate the estimated 280 hot-fire tests the reworked engine will require. Power pack testing is scheduled to start in October at Stennis, using an old Space Shuttle Main Engine stand and turbomachinery pulled from the RS2200 linear aerospike engine PWR predecessor Rocketdyne built to power the canceled X-33 reusable launch vehicle testbed.

Eight of the PWR engines will be used for ground testing, and the remaining two for flight-testing. The first Ares I with an active first stage is scheduled to fly in March 2013, Hanley said.