In 2010 and again in 2011, the Defense Advanced Research Projects Agency (DARPA) suffered two setbacks when it lost both its mach 20 Hypersonic Technology Vehicle 2 (HTV-2) gliders during test flights. Now, in a new report on the HTV-2’s second ill-fated flight in 2011, DARPA says that they believe they know why the the craft failed — but its not all bad news.
But first, the bad news: According DARPA, an engineering review board has concluded that “aeroshell degradation” was the cause of the crash. The going theory is that after separating from its booster rocket and cruising along at 20 times the speed of sound — or 13,000 miles per hour — the outer skin of the vehicle wore away much faster than had been expected. This caused a series of shockwaves, which in turn caused the HTV-2 to roll suddenly.
The investigators say that the HTV-2 was actually able to correct for this for a while, but eventually DARPA says, “the severity of the continued disturbances finally exceeded the vehicle’s ability to recover.” At which point, the HTV-2’s safety system clicked on and brought the craft down into the ocean in a controlled descent into the ocean.
While both tests failed to be completed satisfactorily, DARPA presents some optimistic points. While flying, the craft was able to control for the disturbances it experienced, at least for a little while. This was apparently possible thanks to information gleaned from the first test flight in 2010. While it might be a little bit of a good spin on bad events, it’s worth pointing out that for a few minutes, DARPA appeared to have been able to control a craft traveling through the atmosphere at an unbelievable speed.
DARPA’s announcement seems to also stress that the vehicle’s safety systems operated correctly and terminated the test flight. While that might be a minor point, it’s somewhat comforting that this thing wasn’t hurtling completely out of control at 13,000 miles per hour.
DARPA quotes its acting director Kaigham J. Gabriel as looking at the HTV-2 situation this way:
The initial shockwave disturbances experienced during second flight, from which the vehicle was able to recover and continue controlled flight, exceeded by more than 100 times what the vehicle was designed to withstand […] That’s a major validation that we’re advancing our understanding of aerodynamic control for hypersonic flight.
There is no word from DARPA as to whether or not the program will continue, though it does stress that the test did generate a great deal of useful information about hypersonic flight. Of course, its important to remember that this vehicle was meant to test concepts behind developing a rapid strike platform designed to hit any target in the world within an hour. Perhaps failure isn’t always such a bad thing.
(DARPA, Flight Global, image via DARPA)
