Unmanned U.S. Air Force space plane lands after secret, 2-year mission
[caption id="attachment_2684" align="aligncenter" width="300"] The U.S. Airforce's X-37B Orbital Test Vehicle mission 4 after landing at NASA's Kennedy Space Center Shuttle Landing Facility in Cape Canaveral, Florida, U.S., May 7, 2017. U.S. Air Force/Handout…