Article Posted on : - Oct 19, 2014

Recovery crew members process the X-37B Orbital Test Vehicle at Vandenberg Air Force Base after completing 674 days in space. A total of three X-37B missions have been completed, totaling 1,367 days on orbit. A Boeing photo

VANDENBERG AIR FORCE BASE, CALIFORNIA (AP): A top-secret space plane has landed at an Air Force base on the Southern California coast of the US.

The plane spent nearly two years circling Earth on a classified mission. Known as the X-37B, it resembles a mini space shuttle.

It safely touched down at 9:24 am Friday (Oct 17), officials at Vandenberg Air Force Base said.

Just what the plane was doing during its 674 days in orbit has been the subject of sometimes spectacular speculation.

Several experts have theorised it carried a payload of spy gear in its cargo bay. Other theories sound straight out of a James Bond film, including that the spacecraft would be able to capture the satellites of other nations or shadow China's space lab.

In a written release announcing the return of the craft, the US Air Force only said it had been conducting "on-orbit experiments."

The X-37B programme has been an orphan of sorts, bouncing since its inception in 1999 between several federal agencies, NASA among them. It now resides under the Air Force's Rapid Capabilities Office.

The plane that landed Friday is one of two built by Boeing. This is the programme's third mission, and began in December 2012.

The plane stands 2.9 meters tall and is just almost 9 meters long, with a wingspan under 4.5 meters. It weighs 4,989 kilograms and has solar panels that unfurl to charge its batteries once in orbit.

The Air Force said it plans to launch the fourth X-37B mission from Cape Canaveral, Florida, next year.