US military's X-37B space plane blasts off on secretive mission

Space X's Falcon Heavy rocket returned to the skies Thursday night, launching a mysterious spacecraft for the U.S. military.

The rocket lifted off from NASA's Kennedy Space Center in Florida. It's carrying the military's X-37B space plane.

The uncrewed spacecraft is shrouded in secrecy, and the military is not say where it's going.

Incidentally, a couple hours after the launch dozens of calls were made to 911 and the Federal Aviation Administration in Southern California, with people reporting a blueish white light and flames falling through the sky. It's unclear if that was connected to the spacecraft.

Built by Boeing, the X-37B resembles NASA's retired space shuttles. But they're just one-fourth the size at 29 feet long. No astronauts are needed; the X-37B has an autonomous landing system.

They take off vertically like rockets but land horizontally like planes, and are designed to orbit between 150 miles and 500 miles high. There are two X-37Bs based in a former shuttle hangar at Kennedy.

The Associated Press contributed to this report.