Boeing and ATK have joined the Lockheed Martin Skunk Works team bidding to build the U.S. Defense Advanced Research Projects Agency's (DARPA) Blackswift hypersonic technology demonstrator.

Northrop Grumman is understood not to have bid, making it likely a contract will be awarded to Lockheed by September. The unmanned, reusable turbojet/scramjet-powered Blackswift is planned to fly in 2012.

Under DARPA's Falcon program, Lockheed has completed conceptual design of a demonstrator, the HTV-3X, that forms the basis for the Blackswift. The goal of the demonstration is to take-off conventionally, accelerate to beyond Mach 6, maneuver and return to a runway landing.

Skunk Works also is performing subscale tests of the combined-cycle propulsion system, which comprises a high-Mach turbojet and dual-mode ram/scramjet. The turbine is used for take-off and landing, and to accelerate the vehicle to Mach 4, where the ramjet takes over.

Lockheed has ground-tested inlets and nozzles that are shared by the two engines, says Stephen Walker, deputy director of DARPA's Tactical Technology Office. The challenge is in combining both flowpaths over the Mach range during which both the turbine and ramjet are operating, he says.

DARPA is not discussing Blackswift because it is in source selection, but it will now be a joint program with the U.S. Air Force Research Laboratory, Walker told the AIAA Joint Propulsion Conference here.

The Blackswift will use a round-combustor dual-mode ramjet under development by Pratt & Whitney Rocketdyne. Both Rolls-Royce and Williams International are developing candidates for the 13-inch diameter high-Mach turbine.

Walker will not comment on the number of engines that will power the Blackswift, which will be slightly larger than the Have Blue demonstrator that preceded the F-117 stealth fighter.