The US military’s reusable X-37B spaceplane will launch on the next flight of SpaceX’s Falcon Heavy rocket, scheduled for December 7, officials announced on Wednesday.

This was unexpected because the spaceplane’s six previous missions launched on medium-lift Atlas V or Falcon 9 rockets. This next mission, the seventh by an X-37B spaceplane, will fly on a heavy-lift launcher for the first time.

The payload for the next Falcon Heavy rocket was a secret before the military’s announcement on Wednesday. The mission was known simply by the designation USSF-52, and it will take off from NASA’s Kennedy Space Center in Florida.