DARPA Releases Video of Failed HTV-2 Flight

Via AviationWeek.com -

DARPA says it does not know yet what caused the August 11 second flight of its HTV-2 hypersonic glider to end after just 9min, but it's pretty sure it was not the same anomaly that caused the first flight on April 22 last year to end prematurely, also after just 9min.

The agency has released video of the second flight, captured with a handheld camera by a crewmember on the first telemetry-tracking vessel to catch sight of the HTV-2 as it was released from its Minotaur IV booster to begin what was planned as a 30min, Mach 20 flight across the Pacific to splash down off Kwajalein.

DARPA says the second HTV-2 was in stable, controlled Mach 20 flight for 3min before the anomaly -- longer than was achieved by the first vehicle. But the anomalies on both flights occurred in the same phase of flight -- after release from the booster, when the aerodynamic and reaction controls were guiding the vehicle through atmospheric re-entry and into a pull-up maneuver to control speed and altitude for the glide.

The agency says it appears changes made after the first flight were successful. Center of gravity was adjusted, angle of attack reduced and the reaction control system used to augment aerodynamic control flaps. These changes were made to reduce the vehicle's natural roll-yaw coupling, which on the April flight caused the autonomous flight-termination system to activate when roll exceeded limits.

Changes after Flight 1 were designed to reduce the uncertainty regarding when hypersonic flow over the vehicle would transition from laminar to turbulent, increasing drag and changing flight characteristics. They appear to have been successful in that goal, as initial data "indicates that our pre-flight models successfully predicted transition to within 10 seconds of actual transition point," says DARPA.

If it proves out, that better understanding of laminar to turbulent flow -- achieved through the detail investigation that followed the first failure -- may yet prove to be the major product of the HTV-2 program. It may not sound like much, but DARPA says it will provide a better idea of how far a prompt global strike weapon can fly, and how accurate it will be.