(AP)  An unmanned U.S. Air Force spaceplane that has been in orbit for over a year is coming back to Earth.

The Pentagon's experimental craft, which resembles a mini space shuttle, is slated to land at Vandenberg Air Force Base in California. The exact date depends on weather and other conditions, but the Air Force said Wednesday it expects the landing to occur in early to mid-June.

Officially called the X-37B Orbital Test Vehicle, it blasted off in March 2011 and was the second of its type to be launched.

The first made an autonomous landing in 2010 at Vandenberg after a 270-day mission.

Measuring 29 feet (8.8 meters) long with a wing span of 15 feet (4.5 meters), the latest X-37B has stayed in orbit longer. Its exact mission is largely a mystery.

Explore further No landing date yet for Air Force's mystery craft

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