The test flight of a hypersonic unmanned aerial vehicle over the Pacific Ocean did not go as planned. For the second time, the Defense Advanced Research Projects Agency lost control of the experiment before it was over, tweeting nine minutes into the flight that scientists had lost telemetry with the fastest aircraft ever built. Here’s how DARPA explains it: “Here’s what we know,” said Air Force Maj. Chris Schulz, DARPA HTV-2 program manager and PhD in aerospace engineering.  “We know how to boost the aircraft to near space.  We know how to insert the aircraft into atmospheric hypersonic flight.  We…