Falcon HTV-2, the unmanned hypersonic glider developed for U.S. defense, was lost over the Pacific Ocean yet again, after it was launched atop a rocket on Thursday.

The experimental aircraft took off on Thursday morning from Vandenberg Air Force Base in California, when an Air Force Minotaur IV rocket took HTV-2 to the edge of the Earth's atmosphere.

The aircraft got separated from its protective cover atop the rocket when it reached an undisclosed sub-orbital altitude. After that it dived back to the Earth and start gliding over the Pacific at 20 times the speed of sound, or Mach 20.

The Defense Advanced Research Projects Agency (DARPA) said that contact with the experimental craft was lost after it began flying on its own. More than nine minutes of data was collected before an anomaly caused loss of signal, according to a DARPA statement.

"Here's what we know," said Air Force Maj. Chris Schulz, DARPA's program manager. "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. It's vexing; I'm confident there is a solution. We have to find it."

The arrowhead-shaped aircraft is claimed to be capable of delivering military strike anywhere in the world within an hour.

"We'll learn. We'll try again. That's what it takes," DARPA Director Regina Dugan said in the statement. But the statement contradicted with what DARPA had announced earlier.

Before the test, the agency said that this would be the last HTV-2 flight for the Falcon program, which started in 2003. The first flight of the HTV-2 took place in April, 2010, which ended with the loss of the aircraft after nine minutes of flight. That craft detected an anomaly, aborted its flight and plunged into the ocean, the agency said.

Schulz said that there are three technical challenges within the HTV-2 flight regime - aerodynamic; aerothermal; and guidance, navigation and control. Each phase of flight introduces unique obstacles within these areas.

"To address these obstacles, DARPA has assembled a team of experts that will analyze the flight data collected during today's test flight, expanding our technical understanding of this incredibly harsh flight regime," explained Schulz.