WASHINGTON For the second straight time, controllers lost contact with an experimental U.S. military hypersonic vehicle before it could complete its planned flight profile.

The second Hypersonic Technology Vehicle(HTV)-2 successfully launched April 11 from Vandenberg Air Force Base, Calif., atop a Minotaur 4 rocket, according to the U.S. Defense Advanced Research Projects Agency (DARPA), which is sponsoring the demonstration program. The vehicle successfully separated from the rocket and was on track for the glide phase of its mission, during which it was to demonstrate maneuverability at speeds approaching 20 times the speed of sound, when contact was lost.

DARPA said the vehicle likely splashed down in the Pacific Ocean somewhere along its planned flight path. The agency gathered about nine minutes worth of flight data before the signal loss.

“We know how to boost the aircraft to near space. We know how to insert the aircraft into atmospheric hypersonic flight. We do not yet know how to achieve the desired control during the aerodynamic phase of flight,” Air Force Maj. Chris Schulz, DARPA HTV-2 program manager, said in the Aug. 11 press release. “It’s vexing.”

DARPA said it will now assemble an independent engineering review board to parse the data from the flight. The agency did not say when HTV-2 will fly again — only that it must.

“Prior to flight, the technical team completed the most sophisticated simulations and extensive wind tunnel tests possible. But these ground tests have not yielded the necessary knowledge,” DARPA Director Regina Dugan said in the press release. “Filling the gaps in our understanding of hypersonic flight in this demanding regime requires that we be willing to fly.”

This was the second test flight of the HTV-2, which is designed to demonstrate the aerodynamic properties, materials and guidance of vehicles traveling through the atmosphere at speeds approaching 20,000 kilometers per hour. The vehicle is unpowered; it achieves its testing velocity by being launched to just outside the atmosphere and re-entering at a nearly vertical angle before leveling off for its glide phase.

The first HTV-2 flight, which occurred in April 2010, was cut short when controllers lost telemetry about nine minutes into the mission. “The vehicle’s onboard system detected a flight anomaly and engaged its onboard safety system — prompting the vehicle to execute a controlled descent into the ocean,” DARPA said in a posting on its website.



Hypersonic Vehicle Found To Have Veered Off Course