Mystery surrounds Air Force's secretive X-37B space plane landing plan

http://www.msnbc.msn.com/id/46091282/ns/technology_and_science-space/#.Tx1xAPn4V8E

The United States Air Force's secretive X-37B space plane has been circling Earth for more than 10 months, and there's no telling when it might come down.

As of Friday (Jan. 20), the mysterious robotic X-37B spacecraft has been aloft for 321 days, significantly outlasting its stated mission design lifetime of 270 days. But it may stay up for even longer yet, experts say, particularly if the military views this space mission — the second ever for the hush-hush vehicle — as something of an endurance test.

"Because it is an experimental vehicle, they kind of want to see what its limits are," said Brian Weeden, a technical adviser with the Secure World Foundation and a former orbital analyst with the Air Force.

A long mystery mission
The Air Force launched the X-37B in March 2011, sending the reusable space plane design on its second space mission. The X-37B now zipping around our planet is known as Orbital Test Vehicle-2, or OTV-2.

Another X-37B vehicle, the OTV-1, launched in April 2010 and landed in December of that year, staying on orbit for 225 days — well under the unmanned spacecraft's supposed 270-day limit. But OTV-2 has already exceeded that limit by more than seven weeks, and the calendar keeps turning over. [ Photos of the 2nd Secret X-37B Mission ]

Racking up a lot of time in space might be a key part of the current mission, according to Weeden.

"I think they didn't want to push it, just because it was the first of its kind," he told SPACE.com, referring to OTV-1's flight. "But I think that they are looking to push the second one."