Black clouds from the west roll past the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida.

Shortly after 8 p.m. EDT, black clouds from the west roll past the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. The center is in launch mode as the countdown continues for liftoff of space shuttle Discovery at 1:36 a.m. EDT Aug. 25 on the STS-128 mission. Weather plays a significant role in any launch attempt. Forecasters give only 20 percent probability of weather prohibiting launch. Discovery's 13-day mission will deliver more than 7 tons of supplies, science racks and equipment, as well as additional environmental hardware to sustain six crew members on the International Space Station. The equipment includes a freezer to store research samples, a new sleeping compartment and the COLBERT treadmill. The mission is the 128th in the Space Shuttle Program, the 37th flight of Discovery and the 30th station assembly flight. Photo credit: NASA/Troy Cryder