The X-37B Orbital Test Vehicle (OTV), the Air Force’ unmanned, reusable space plane. (US Air Force / AFP)

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WASHINGTON — The ’s mysterious robot space plane is expected to this week after a 22-month orbit, officials said Tuesday, but the craft’s remains shrouded in secrecy.
The unmanned X-37B, which looks like a miniature space shuttle, is due to glide back to Earth after having launched on Dec. 11, 2012, on a mission that military officers say is strictly secret.
“Preparations for the third of the X-37B are underway at Vandenberg Air Force Base” in California, said a US Air Force spokesman, Captain Chris Hoyler.

A said that the space plane will likely touch down sometime this week and that future missions would seek to extend the vehicle’s technical capabilities and time in orbit.

“The specific parameters are unreleasable,” the official said.

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

The X-37B, manufactured by aerospace giant , weighs five tonnes and measures about 29 feet (8.8 meters) long, with a wing span of roughly 15 feet across.

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