By Guy Norris/AviationWeek.com

Test officials are trying to work out why the final flight of a hypersonic weapon technology demonstrator ended in failure after less than one minute of flight over the Pacific, says the Defense Advanced Research Project Agency (Darpa).

The test, conducted with the U.S. Office of Naval Research, Aerojet and Boeing, was believed to be the last attempt in the Darpa-led effort to evaluate the weapon's rocket-boosted ramjet-scramjet propulsion system, also known as a dual-combustion ramjet (DCR). A previous test on Sept. 25, 2007, was only partly successful, failing to accelerate to the planned Mach 5 test condition, reaching only Mach 3.5 following issues with the fuel system.

The September flight test was intended to demonstrate DCR take-over, fuel control and climb and acceleration to Mach 5, while the last test, which took place on January 16, was aimed at Mach 6 and measurements of terminal accuracy. The HyFly cruise vehicle was launched at 3:23pm PST, from a Boeing F-15E over the U.S. Navy's sea range at the Naval Air Warfare Center Weapons Division, Point Mugu, Calif, "but was unsuccessful," says Darpa. "The scramjet engine did not operate as expected and after approximately 58 seconds of flight, the vehicle impacted the ocean. We're reviewing flight data and no further details are available," the agency adds.

HyFly was being evaluated as a potential high-speed weapon for both air and ship-launch against options such as Boeing's scramjet-powered X-51A and Lockheed Martin's turbine-powered Rattlrs, which stands for Revolutionary Approach to Time-Critical Long-Range Strike. It was considered slightly lower risk as it has a lower Mach number (M3.3) at which the engine can be started than a pure scramjet, but the issues encountered during the tests may prompt a risk reassessment.

The test failure will be viewed as a big disappointment for supporters of the DCR concept originally developed by Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. The DCR is based on an innovative cycle relying on a first stage that burns liquid hydrocarbon fuel (JP-10) in a subsonic ramjet to generate a fuel-rich gas. That fuel-rich gas byproduct is then itself burned in a supersonic-combustion ramjet. Other key technologies explored in the HyFly program included the advanced structure of the DCR which was made from a ceramic matrix composite.

There was no comment from Darpa or the other team members as to whether any further test attempts are feasible, or what future work may be in store for the DCR concept.

Image: DARPA