DARPA, the Defense Advanced Research Project Agency, has released an explanation for why the HTV-2 glider, the Hypersonic Technology Vehicle, test flight failed last year. The spacecraft achieved Mach 20, about 13,000 MPH, for roughly 3 minutes before it plunged into the Pacific Ocean. The Engineering Review Board, ERB, has gone over the data and blames a series of shockwaves for damaging the craft′s aero-shell, a special thermal resistant material to protect the vehicle from the extreme temperatures. The shell coating about the vehicle began to peel off, making the HTV-2 unstable in flight. The shockwaves began about 9 minutes into the flight and were reported to be significantly higher, as much as 100 times more than the designed strength of the shell. As the anomaly worsened, the craft′s automatic controls ended the flight and led to a controlled descent into the Pacific Ocean.
The HTV-2 is is a testbed for developing future space-planes, vehicles capable of making long-distance, sub-orbital flights at extremely high speeds. Hypersonic is normally considered any speed above Mach 5, about 3,250 MPH. Conventional jetliners fly at speeds below Mach 1, usually between 500-600 MPH. The goal of these tests is to develop the technology for a new breed of aircraft which can take-off from a runway like a jetliner, operate at the fringe of space at speeds in excess of Mach 8, about 5,200 MPH, then gently glide back for a controlled landing at another runway half a world away, all in less than 90 minutes.
Currently, flights across the Pacific from the United States to Asia can take more than half a day. So cutting the flying time down to less than 2 hours would be a huge leap forward. A technology platform such as the HTV-2 could eventually also lead to a reusable space-plane which could even achieve low Earth orbit, which requires speeds of 17,600 MPH, or Mach 24.44 or more. Some of the earliest research in hypersonic space-planes stems from Nazi Germany. Professors Eugen Sanger and Irene Bredt envisioned a rocket-bomber, known as the Silbervogel, or Silver Bird, which would skim the edge of space after launching from a rocket-assisted rail system. The basic concept became the basis for later development of lifting body airframes, which eventually led to the U.S. Space Shuttle.
Now that DARPA has determined what went wrong in last year′s test flight of the HTV-2 glider, changes to the hypersonic craft′s aero-shell can be made to make it more resistant to the unexpectedly strong shockwaves which caused the flight′s failure. Science marches forward with each new discovery, even those resulting from a failure. No word has been given yet as to when a third flight will be attempted by the HTV-2.