Revealed: How America's secret space plane has been in orbit for over a year - and no one knows what it's doing The X-37B has been circling the Earth at 17,000mph and was due to land in California in December 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 Calif