Traveling  at hypersonic speed . . .

. . .  ain't for sissies. Or aircraft with (relatively) thin skins, apparently.

DARPA's hypersonic HTV-2 test flight back in August was a great success, considering that the aircraft went some twenty times the speed of sound.

Before it crashed, that is.

Why? No one was sure until recently, when a report from an engineering review board decided it had gone so fast it lost its skin:

The ERB [Engineering Review Board]concluded that the “most probable cause of the HTV-2 Flight 2 premature flight termination was unexpected aeroshell degradation, creating multiple upsets of increasing severity that ultimately activated the Flight Safety System.”

Based on state-of-the-art models, ground testing of high-temperature materials and understanding of thermal effects in other more well-known flight regimes, a gradual wearing away of the vehicle’s skin as it reached stress tolerance limits was expected. However, larger than anticipated portions of the vehicle’s skin peeled from the aerostructure. The resulting gaps created strong, impulsive shock waves around the vehicle as it travelled nearly 13,000 miles per hour, causing the vehicle to roll abruptly. Based on knowledge gained from the first flight in 2010 and incorporated into the second flight, the vehicle’s aerodynamic stability allowed it to right itself successfully after several shockwave-induced rolls. Eventually, however, the severity of the continued disturbances finally exceeded the vehicle’s ability to recover.

DARPA release on the report.

An artist's rendering of HTV-2. A hypersonic aircraft could fly from the U.S. to a target across the globe in under an hour.