SUMMERLAND KEY, Fla.– The U.S. Air Force has added ATK Launch Systems Group of Salt Lake City to its hypersonic flight research program in response to a congressional earmark and strong support from the service’s chief scientist, according to Air Force and company officials.

With NASA largely out of the hypersonic flight business, the Air Force Research Laboratory at Wright Patterson Air Force Base in Ohio now is leading the U.S. quest to develop an alternative to rocket-powered launchers and high-speed vehicles . These new vehicles would be propelled by engines called supersonic combustion ramjets, or scramjets, that draw their oxygen directly from the atmosphere. Traditional rocket engines must carry condensed oxygen with them, and that sacrifices mass and volume that could otherwise be used for bombs, satellites or reconnaissance sensors.

The Air Force Research Laboratory is conducting wind-tunnel tests on components of a proposed test vehicle called the X-51A, which is scheduled to fly for the first time in 2009. Boeing Integrated Defense Systems of St. Louis is building four X-51 test vehicles, and Pratt & Whitney Rocketdyne of Canoga Park, Calif., is building scramjet engines to power them. The X-51A vehicles would be dropped from a B-52 aircraft in the series of tests and not recovered. The ultimate design goal, however, is a re usable, scramjet-powered, launch vehicle.

In late April , the Air Force awarded ATK a $3.9 million contract to explore the possibility of flight testing an alternate engine on the X-51 airframe. ATK officials have designed and tested a prototype of the engine at the company’s GASL facility in Ronkonkoma, N. Y. , using internal company research funds.

GASL is best known for building the engine that NASA tested successfully on the X-43A hypersonic vehicle in 2004.

ATK hopes its new engine eventually will power a second version of the X-51 to be called the X-51B.

“This is really not a knock on the Pratt & Whitney engine,” said Air Force Chief Scientist Mark Lewis, referring to the decision to start looking at a second engine. “What it really is saying is that there are different approaches that we could take, and it’s not immediately obvious what the best approaches are. “

For now, the Air Force Research Laboratory has no plans go beyond preliminary work on an X-51B.

“Right now, [ATK officials] have a congressional add for 2007 to look at a conceptual design layout as to what that configuration would be, and to do some inlet studies and things like that. Anything past that is still open for debate,” said Charlie Brink, the Air Force Research Laboratory’s X-51A program manager, who also will oversee the ATK work.

The X-51 program is geared toward improving access to space, but ATK officials have been lobbying the Air Force, including Lewis, to test their engine for a spin-off application: a hypersonic cruise missile capable of destroying targets anywhere in the world in a matter of minutes.

“We call it the high-speed strike weapon,” said Charlie Precourt, vice president of strategy and business development for ATK’s Launch Systems Group. Precourt said a hypersonic missile would be simpler to build than a space vehicle. “We think it would make sense to evolve a hypersonic engine cruiser to that kind of system first, and go from there,” he said.

Brink said ATK’s contract has not changed the overall direction of the X-51 program as an access-to-space effort led by the consortium of Boeing and Pratt & Whitney Rocketdyne.

“It’s important to remember that the purpose of the ATK effort — and remember, they got a congressional add to look into this — would be a weapons application,” Brink said.

Brink pointed out that $160 million is scheduled to go to the Boeing team , compared to $3.9 million for the ATK contract. “I just want to show you the scope of things. Not to diminish ATK’s work. They should be excited,” he said.

The ATK and Pratt engines have significantly different internal designs, or flow paths, Lewis said . Pratt & Whitney’s engine is designed for testing propulsion from Mach 4.5 through Mach 6.5, one of the technically trickiest ranges for a scramjet to cover on its way to orbit. The ATK engine would focus on Mach 5.0, a speed suitable for a cruise missile, said ATK and Air Force officials.

Precourt said his company’s engine is smaller and would give Air Force officials the option of incorporating a parachute-recovery system on the test vehicle.

With the Pratt & Whitney engine design, the Air Force ” didn’t have room for things like recovery systems and recover chutes. Our engine has the potential to give them that flexibility . So we’re studying that with them now,” Precourt said.