For the second time in a row, the Falcon HTV-2, the unmanned hypersonic glider developed by the Defense Advanced Research Projects Agency (DARPA) for the U.S. defense failed its test flight and got lost over the Pacific Ocean on Thursday.

The $308 million experimental aircraft, claimed to be the world's fastest aircraft with a capacity of covering 13,000 miles in an hour, was launched atop an Air Force Minotaur IV rocket on Thursday morning from Vandenberg Air Force Base in California. 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.

According to DARPA, contact with the experimental craft was lost after it began flying on its own. It's the second time since April this year that the research agency has lost a HTV-2 aircraft during test flight. The first flight of the HTV-2 in April also ended with the loss of the aircraft after nine minutes of flight. DARPA said that craft detected an anomaly, aborted its flight and plunged into the ocean.

Again this time, the arrowhead-shaped HTV-2 aircraft detected before an anomaly, which caused loss of signal, DARPA said in a statement. The aircraft is claimed to be capable of delivering military strike anywhere in the world within an hour.

Washington could even use the HTV-2 aircraft to strike an Iranian atomic facility or hit a North Korean missile prior to liftoff. It can also be employed against a critical terrorist location if other weapon fails to carry out the attack, New York Times reported.

"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."

Will the Falcon HTV-2 program continue?

"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. Now, considering the setbacks of the vehicle, it's likely that the Air Force or any other military service might hesitate to take control of the program.

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.