SpaceX has launched the Air Force's super-secret space shuttle.

An unmanned Falcon rocket blasted off Thursday from Florida's Kennedy Space Center. It's the fifth flight for one of these crewless mini shuttles, known as the X-37B Orbital Test Vehicle.

The two Air Force space planes have already logged a combined 5 years in orbit. But officials won't say what the spacecraft is doing up there.

The last mission lasted almost two years and ended with a May touchdown at the runway formerly used by NASA's space shuttles.

As usual, SpaceX aims to land its leftover booster back at Cape Canaveral for eventual reuse.

This is the first time SpaceX has provided a lift for the experimental mini-shuttle.