(The Blaze/AP)– A secretive unmanned space plane is staying in orbit a little longer.

Mission Extended For Secretive Orbiting Air Force UAV

The experimental Air Force craft has been circling Earth for about nine months. The X-37B orbital test vehicle was due to land in California this week, but the Air Force said Tuesday that the mission will be extended. A landing date has not been set.

The plane resembles a mini space shuttle and is the second to fly in space. The first one landed itself last December at Vandenberg Air Force Base in California after more than seven months in orbit.

The  X-37B is the second spacecraft built for the Air Force by Boeing’s Phantom Works. It carries the name Orbital Test Vehicle 2, or OTV-2.

The Air Force has said the second mission was to further test the craft, but the ultimate purpose has largely remained a mystery.

Here is some video of the secretive X-37B in action: