Back in August, the U.S. Military's Defense Advanced Research Projects Agency, or DARPA, conducted the second test flight of their experimental hypersonic vehicle, the HTV-2. The project was part of a data collecting mission, a way to test global strike capabilities. DARPA said that their goal was to be able to "reach anywhere in the world in less than an hour."
If that sounds like a lofty goal, it's actually more within reach than you may think. The HTV-2 was capable of reaching speeds of 13,000 MPH, or 3.6 miles per second. That's about 22 times as fast as a commercial airplane.
"The flight successfully demonstrated stable aerodynamically-controlled flight at speeds up to Mach 20 (twenty times the speed of sound) for nearly three minutes," says DARPA. But as we know, the glider experienced a series of traumas that resulted in the abortion of the flight.
Now, we know why: Unexpected aeroshell degradation. Or simply put, the glider's shell started ripping off.
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.
Kind of the byproduct of hitting temperatures of 3,500 Fahrenheit and beyond, I guess.
Although the flight experienced problems, DARPA says that the data collected serves as a "profund advancement" for the project. They can use what they learned in future experiments - for instance improving upon the outer shell of the hypersonic vehicle by readjusting heat-stress allowances and better preparing for "thermal uncertainties."
At current speeds, the HTV-2 could get from New York to Los Angeles in less than 12 minutes. Isn't technology amazing?