Front view of the X-37B on the shuttle runway at the Kennedy Space Center. Engineers wear protective suits so they will avoid contamination by any volatile chemicals. (US Air Force photo from Spaceflightnow.com)
The fourth X-37B mission has finally come to an end. Currently the US Air Force has two X-37 spacecraft (that we know of), and this was spacecraft number - well, we don't know, because the US Air Force does not officially disclose which of its spacecraft are up there during a mission. We DO know that it lifted off on May 20, 2015, on an Atlas 5 booster from Cape Canaveral LC-41. It spent 718 days in space.
Side view of the X-37B. (US Air Force photo from Spaceflightnow.com)
For more information on this mission, check out SpaceFlightNow.com: