As the final minutes count down toward the 5:42 a.m. liftoff of the SpaceX Falcon 9 rocket and Dragon spacecraft, there are some significant milestones clearing the way toward launch. The Falcon 9’s Merlin engines will be chilled to condition them before they come in contact with cryogenic propellants. The strongback, a gantry-like support structure at Space Launch Complex 40, will lower away from the rocket. Finally, the Eastern Range and the SpaceX launch director each will give a final approval to launch.