The past and future of America’s space arsenal intersected, briefly, in the summer of 2011. For two weeks in July, NASA’s Space Shuttle Atlantis roughly shared its Earth orbit with the Air Force’s X-37B, a 29-foot-long, highly maneuverable robotic spacecraft that entered service in early 2010 and has been cloaked in secrecy ever since. The X-37 was around 80 miles higher than the Shuttle, so it’s doubtful the four-person Atlantis crew, conducting the 135th and last Shuttle mission, ever saw the robotic craft. The X-37′s small size — barely a quarter the length of Atlantis — made a sighting even less likely.