On April 22, 2010, the U.S. Air Force launched the super-secret X-37B space plane on its first spaceflight. [‘On This Day in Space’ Video Series on Space.com]

This space plane is also known as the Orbital Test Vehicle. It looks a lot like NASA's space shuttle, only it's much smaller and doesn't have any windows. But the X-37B doesn't need windows anyway, because no one actually flies in it. It's completely autonomous and can even land on a runway without a human pilot. The X-37B has flown several highly classified payloads on long-duration missions. For its first flight, the X-37B launched on an Atlas V rocket from Cape Canaveral and it orbited the Earth for 224 days. The Air Force never disclosed what kind of experiments were going on during that time.