At Kennedy Space Center’s Launch Complex 39A, valves are open and propellants are beginning to flow into the SpaceX Falcon 9 rocket. Atop the rocket is the SpaceX Crew Dragon spacecraft, with two NASA astronauts – Robert Behnken and Douglas Hurley – safely strapped inside. Liftoff on NASA’s SpaceX Demo-2 mission to the International Space Station remains planned for an instantaneous launch window at 4:33 p.m. EDT.