The countdown clock at the NASA Press Site ticks off the seconds following liftoff of the Falcon 9 rocket from Space Launch Complex 40.

The countdown clock at the NASA Press Site ticks off the seconds following liftoff of the Falcon 9 rocket from Space Launch Complex 40 on Cape Canaveral Air Force Station in Florida, carrying the SpaceX CRS-4 mission to orbit. Liftoff was at 1:52 a.m. EDT.

The mission is the fourth of 12 SpaceX flights NASA contracted with the company to resupply the space station. It will be the fifth trip by a Dragon spacecraft to the orbiting laboratory. The spacecraft’s 2.5 tons of supplies, science experiments, and technology demonstrations include critical materials to support 255 science and research investigations that will occur during the station's Expeditions 41 and 42. To learn more about the mission, visit http://www.nasa.gov/mission_pages/station/structure/launch/index.html. Photo credit: NASA/Frankie Martin