Mystery Mini Space Shuttle Landing Delayed

June 15, 2012 -- It's a bird! It's a plane! It's a mysterious unmanned mini-space shuttle on a classified mission.

But it won't be landing today.

The Air Force has delayed landing for the X-37B, an unmanned aircraft built by Boeing that has spent more than a year on a classified mission in space.

Weather conditions were not favorable for the landing today. Officials said the craft could land Saturday. A landing window for the X-37b lasts through June 18.

Measuring 29 feet in length and having a 15-foot wingspan, the unmanned reusable X-37B Orbital Test Vehicle looks like a miniature version of NASA's now retired space shuttles.

The craft went into orbit on March 5, 2011, but as was the case during its first launch in 2010, very little has been known about its mission or what payloads it might be carrying because its missions were classified. That has led to speculation that the spacecraft is involved in intelligence gathering operations or the testing of new technologies.

Jeremy Eggers, a spokesman for the 30th Space Wing at Vandenberg AFB, told ABC News any landing is a "day-by-day situation based on the conditions."

In keeping with the scarce mission details for the X-37B, even the initial announcement of an upcoming landing was kept vague. A May 30 Air Force statement said the spacecraft would return to earth in the "early- to mid-June time frame."

Designed to stay in extended Earth orbits, the X-37B remained in orbit for 225 days during its maiden mission in 2010. It will have spent almost twice as much time in orbit this time around.