<p>After spending about 22 months orbiting the Earth on a secret mission, a US Air Force X-37B unmanned, reusable space plane has finally returned.<br /><br /></p>.<p>The spacecraft which blasted off in December 2012 for its third space mission touched down at California's Vandenberg Air Force Base Friday, Xinhua reported.<br /><br />"The mission is our longest to date and we're pleased with the incremental progress we've seen in our testing of the reusable space plane," the US Air Force said in a statement.<br /><br />The programme is being run by the Air Force's Rapid Capabilities Office, and there are two space planes in the fleet, both built in tight secrecy by Boeing.<br /><br />The X-37B space planes look much like NASA's retired space shuttles, only much smaller. Each X-37B spacecraft is about 8.8 metres long and 4.5 metres wide.<br /><br />The aim of the spacecraft is to "demonstrate a reliable, reusable, unmanned space test platform for the US Air Force," the statement added.</p>
<p>After spending about 22 months orbiting the Earth on a secret mission, a US Air Force X-37B unmanned, reusable space plane has finally returned.<br /><br /></p>.<p>The spacecraft which blasted off in December 2012 for its third space mission touched down at California's Vandenberg Air Force Base Friday, Xinhua reported.<br /><br />"The mission is our longest to date and we're pleased with the incremental progress we've seen in our testing of the reusable space plane," the US Air Force said in a statement.<br /><br />The programme is being run by the Air Force's Rapid Capabilities Office, and there are two space planes in the fleet, both built in tight secrecy by Boeing.<br /><br />The X-37B space planes look much like NASA's retired space shuttles, only much smaller. Each X-37B spacecraft is about 8.8 metres long and 4.5 metres wide.<br /><br />The aim of the spacecraft is to "demonstrate a reliable, reusable, unmanned space test platform for the US Air Force," the statement added.</p>