The Guardian (UK) reports: “‘Secret space plane’ is a phrase that sidles comfortably alongside ‘undersea lair’ and ‘diamond laser’ as an apparent invention of spy movies and science fiction. But like both those things, secret space planes exist.”  

“Beyond the fact of their existence, however, the US military keeps quiet about its pair of planes – and says even less about what one was doing for two years in orbit before landing in California last week.”  

“Silence from the US air force, however, does not discourage an educated guess or idle speculation, the latter of which tends to flourish especially when something is stamped ‘classified’ and just came back from outer space.”