Unmanned Space Plane to Land at Vandenberg Air Force Base

The U.S. military plans to land its secretive X-37B spacecraft, which has been circling Earth for nearly two years, at Vandenberg Air Force Base on Tuesday.

The exact time and date will depend on weather and technical factors, according to air force officials.

The experimental, robotic space plane is returning from a 22-month classified orbital mission.

The nine-meter-long spaceship, which resembles a miniature space shuttle, had its maiden flight in April 2010, returning after eight months. A second vehicle launched in March 2011 and stayed in orbit for 15 months.

The X37-B space plane, also know as the Orbital Test Vehicle, blasted off for its second mission aboard an unmanned Atlas 5 rocket from Cape Canaveral Air Force Station in Florida on Dec. 11, 2012.

The military has said the vehicles, built by Boeing, are designed to test techonologies, though details of the missions are classified.

Last week, the air force and NASA finalized a lease agreement to relocated the X-37B program to Florida’s Kennedy Space Center from California.