Air Force's Mysterious X-37B Space Plane Wings by 600 Days in Orbit

The U.S. Air Force's mysterious X-37B space plane has now spent 600 days in Earth orbit on the vessel's latest mission, and is nearing a program record for longest time spent in space. The robotic X-37B lifted off atop a United Launch Alliance Atlas V rocket from Florida's Cape Canaveral Air Force Station on May 20, 2015, kicking off the program's fourth space mission (which is known as Orbital Test Vehicle-4, or OTV-4). The first OTV mission began on April 22, 2010, and concluded on Dec. 3 of t