Last week, the Defense Advanced Research Projects Agency (DARPA) suffered a serious setback… maybe. Early on Thursday, the agency launched the fastest airplane ever constructed. It isn’t sure exactly what happened next. Minutes after the aircraft took flight, DARPA lost contact with it. The plane was flying at Mach 20 when it disappeared. An Air Force spokesman says even seemingly unsuccessful tests like this one yield new data and contribute to summiting the learning curve of high-speed flight.