Mystery: U.S X-37B space plane has been in orbit for over a year

Mystery: U.S X-37B space plane has been in orbit for over a year: "The U.S Air Force’s highly secret unmanned space plane was supposed to stay in space for nine months, but it’s now been there for a year and three days – and no one knows what it’s doing.

The experimental craft has been circling Earth at 17,000 miles per hour and was due to land in California in December.

However the mission of the X-37B orbital test vehicle was extended – for unknown reasons."