Mysterious US spaceplane returns to Earth

Last updated at 07:37
Secret planeAP

An unmanned US plane on a top-secret, two-year mission to space has returned to Earth and landed in California.

The aircraft, which looks like a miniature space shuttle, is known as the Orbital Test Vehicle or X-37B and spent 674 days in orbit around the planet.

It touched down at Vandenberg Air Force Base on Friday morning.

Air Force officials have only told US media the aircraft performs "risk reduction, experimentation and concept-of-operations development for reusable space vehicle technologies".

This has led to different theories about what it was used for.

The X-37B appeared at Vandenberg Air Force Base in California on 3 December 2010AP
A fourth X-37B mission is planned for 2015
The US Air Force's X-37B appeared at Vandenberg Air Force Base in California on 3 December 2010Reuters
The secret spaceplane is built by manufacturer Boeing