After more than a year in orbit the Air Force's mysterious mini-space shuttle is set to land at Vandenberg Air Force Base in California sometime this week. Air Force officials say a landing could come as early as Wednesday.

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

The reusable spacecraft 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 are 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 30 th Space Wing at Vandenberg AFB told ABC News that the spacecraft's first available landing opportunity will be Wednesday, depending on weather and technical conditions. The landing window extends through June 18, but Eggers says 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.