The U.S. Air Force is set to successfully launch a Boeing X-51 for 300 seconds of hypersonic flight By the end of this month, the U.S. Air Force will begin a series of hypersonic tests that will send a scramjet into the atmosphere for about five minutes, at nearly five times the speed of sound. A scramjet is a supersonic combustion ramjet, while a ramjet is a jet engine using the engine's forward motion to compress air. If all goes as planned, this will be the first time that an aircraft will have flown at such speeds for more than...