A TOP-SECRET U.S. robot space plane landed back on earth Friday after a 22-month orbit, although the craft’s mission remains shrouded in mystery.

    The unmanned X-37B, which looks like a miniature space shuttle, glided into Vandenberg Air Force Base in California on Friday. The vehicle was launched Dec. 11, 2012, on a mission that military officers say is still strictly secret.

    “I’m extremely proud of our team for coming together to execute this third safe and successful landing,” Colonel Keith Balts, commander of the U.S. military’s 30th Space Wing, said after the touchdown.

    Analysts say the X-37B, which is also known as the Orbital Test Vehicle, could be a platform for spying from space, including possibly snooping on other countries’ satellites.

    But officials have previously denied the project had anything to do with creating a “space weapon” that could knock down other satellites.

    The U.S. Air Force says the X-37B can test technology for “reusable” spacecraft and conduct unspecified experiments that can be studied on earth.

    It said the orbiters “perform risk reduction, experimentation and concept-of-operations development for reusable-space-vehicle technologies.”

    The total costs of the program and budget line items associated with it are likewise classified.

    The latest mission was the third and the longest so far for the vehicle.

    An initial flight launched in 2010 lasted about eight months and a second flight had the spacecraft in orbit for more than 15 months.

    The X-37B, manufactured by aerospace giant Boeing, weighs 5 tons and measures about 8.8 meters long, with a wingspan of roughly 4.5 meters.

    Travelling at 25 times the speed of sound, the vehicle is launched into space on the back of a rocket and, once its mission is complete, returns from orbit like a plane.

    But unlike the U.S. space agency Nasa’s civilian shuttle, it has two stabilizers in the rear instead of one, forming a “V” shape. (SD-Agencies)