Hypersonic HTV-2 bails at Mach 20

Following a seven-month scientific investigation, DARPA has released the cause of the early termination of the Mach 20 flight of the HTV-2 hypersonic flight last August.

The HTV-2 is an unpowered glide test vehicle, accelerated to Mach 20 (21,000 kph, 13,000 mph) atop a Minotaur IV rocket, and released at a classified altitude to re-enter the atmosphere and make a controlled hypersonic glide. A lot about how it works is classified, but it does have maneuvering capability at that speed.

During the flight, the vehicle's carbon skin began to peel. That resulted in an irregular surface, which caused shockwaves. Shockwaves are like hammers beating on an aircraft, and these disturbed the vehicle's attitude. It was able to recover and continued flying, but as the peeling increased, the shockwaves eventually produced attitude disturbances 100 times greater than the vehicle was designed to withstand. At this point the flight was aborted and the vehicle was commanded to crash straight down into the Pacific Ocean.

But it's not all bad news. This data is exactly what we needed to get, and pushing it all the way to failure gives the broadest possible data. These vehicles are designed as one-way flights into the ocean anyway, and are not intended to be recovered, so there was no real loss.

Next stop? Better materials, and better control systems.