Watch a live view of the Atlas 5 launch pad with countdown audio (members only)

The U.S. Space Force says it will launch two GPS navigation satellites on reused Falcon 9 boosters next year through a restructured contract with SpaceX that saved taxpayers $52 million, the first time the military has agreed to fly operational national security payloads on previously-flown rockets.

United Launch Alliance ground crews on California’s Central Coast are gearing up to send a classified U.S. government spy satellite into orbit as soon as Monday — weather permitting — aboard one of the company’s four remaining Delta 4-Heavy rockets.

Towering more than 20 stories tall, the 8-million-pound mobile gantry at the Atlas 5 rocket’s launch pad at Vandenberg Air Force Base, California, was retracted into position late Friday for liftoff of NASA’s InSight mission to Mars.