DARPA has confirmed the splash down of its unmanned Falcon Hypersonic Technology Vehicle (HTV-2) following the hypersonic vehicle's second test flight on August 11. While a "controlled descent" generally refers to a human directing and guiding an aircraft to an unscheduled landing, safety systems onboard the HTV-2 kicked in after an anomaly was detected a little over nine minutes into the test flight and autonomously directed it into the ocean.

"We've confirmed that the HTV-2 made impact with the Pacific Ocean along its flight trajectory as planned in the event of an anomaly," explained Air Force Maj. Chris Schulz, DARPA HTV-2 program manager and PhD in aerospace engineering. "This flight safety system is a significant engineering advance in that the system prompts a vehicle to monitor the parameters under which it is operating and exercise safety protocols completely autonomously should those parameters be breached."

DARPA says that changes made to the vehicle following the first test flight, which also ended with a controlled descent into the Pacific, appear to have been effective and aren't being blamed for the anomaly detected during the second test flight. These changes include adjusting the HTV-2's center of gravity, decreasing the angle of attack and using the onboard reaction control systems to augment vehicle flaps during the second test flight.

"According to a preliminary review of the data collected prior to the anomaly encountered by the HTV-2 during its second test flight," said DARPA Director Regina Dugan, "HTV-2 demonstrated stable aerodynamically controlled Mach 20 hypersonic flight for approximately three minutes. It appears that the engineering changes put into place following the vehicle's first flight test in April 2010 were effective. We do not yet know the cause of the anomaly for Flight 2."

Having successfully separated from the Minotaur IV launch vehicle and transitioned to Mach 20 flight on the second test flight, the anomaly appears to have occurred as the HTV-2 attempted to enter the glide phase of flight. DARPA says an independent Engineering Review Board will attempt to identify the most probable cause of the latest anomaly over the coming weeks.