This Saturday has seen the enormous Stratolaunch satellite launcher aircraft take off from the Mojave desert north of Los Angeles. The six-engined megajet with the wingspan of an American football field is the product of Stratolaunch Systems, the company founded in 2011 by the late Microsoft co-founder Paul Allen. It is described as 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.