On May 7, 2017 at 11:47 UTC the U.S. Air Force's X-37B unmanned space plane returned back to Earth. The plane touched down on runway 15 the Kennedy Space Center. The X-37B space plane spent 717 days, 20 hours and 42 minutes in space. It was the fourth flight for the unmanned test project, an enigmatic program that has used twin reusable vehicles. OTV means Orbital Test Vehicle. The X-37B space plane was launched like a satellite atop Atlas 5 rockets and then landed like an airplane.