Liftoff of a previously-flown Falcon 9 rocket is set for 6:27 p.m. EDT (2227 GMT) Thursday from NASA’s Kennedy Space Center in Florida, the first time SpaceX has reused one of its first stage boosters on a second mission. Ground crews face a tight timeline to ready the rocket and the SES 10 communications satellite in time for a Thursday launch attempt.

The head of the launch enterprise directorate at the U.S. Air Force’s Space and Missile Systems Center, Claire Leon, spoke with reporters March 15 about the military’s award of a GPS launch contract to SpaceX, and she discussed plans for more head-to-head launch contract competitions in the coming months.

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tall, the 8-million-pound mobile gantry at the Atlas 5 rocket’s launch pad at Vandenberg Air Force Base, California, was retracted into position late Friday for liftoff of NASA’s InSight mission to Mars.