The U.S. Air Force's X-37B space plane blasted into Earth orbit today, kicking off the robotic vehicle's clandestine fourth mission — as well as the first flight of a tiny solar-sailing spacecraft. <br /> <br />"We are excited about our fourth X-37B mission," Randy Walden, director of the Air Force Rapid Capabilities Office, said in a statement late last month. "With the demonstrated success of the first three missions, we're able to shift our focus from initial checkouts of the vehicle to testing of experimental payloads." <br /> <br />A United Launch Alliance Atlas V rocket launched the AFSPC-5 mission for the U.S. Air Force on May 20, 2015, from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Florida. The mission is the 4th flight of the mysterious X-37B space plane, also known as the Orbital Test Vehicle. See photos from the mission, called OTV-4, here. At Left: The X-37B space plane is seen after landing at Vandenberg Air Force Base in California to end its third mission in October 2014.
