[I]n the desert north of Los Angeles, a gigantic, six-engined megajet with the wingspan of an American football field flew Saturday morning for the first time. Stratolaunch Systems, the company founded in 2011 ... conducted the first test flight of the world's largest plane. Stratolaunch aircraft is a giant flying launch pad, designed to hurtle satellites into low Earth orbit. It aims to offer the military, private companies and even NASA itself a more economical way to get into space. The aircraft's wingspan measures 385 feet -- wider than any airplane on the planet. From tip to tail, it's 238...