UPDATE 1-US military spaceplane poised for 7th launch, first atop SpaceX Falcon Heavy

The U.S. military's secretive X-37B robot spaceplane was poised for liftoff from Florida on Monday on its seventh mission to orbit, the vehicle's first launch atop a SpaceX Falcon Heavy rocket capable of lofting it higher than ever before. The Falcon Heavy, composed of three reusable rocket cores strapped together, was due for blast-off from NASA's Kennedy Space Center at Cape Canaveral during a 10-minute nighttime launch window starting at 8:14 p.m. EST (0114 GMT Tuesday), weather permitting. The Defense Department has disclosed few details about the mission, conducted by the U.S. Space Force as part of the National Security Space Launch program.