KENNEDY SPACE CENTER, FLA. - The aft skirt and lower segment of the Solid Rocket Booster (SRB) being prepared for Return to Flight on mission STS-114 move through the open doors of the Vehicle Assembly Building. The segments will be prepared for stacking with the other segments arriving later. Two SRBs support the liftoff of the Space Shuttle on a launch. The twin 149-foot tall, 12-foot diameter SRBs provide the main propulsion system during launch to place the 180,000-pound orbiters in the proper orbit around the Earth. They operate parallel with the Space Shuttle main engines for the first two minutes of flight and jettison away from the orbiter with help from the Booster Separation Motors, about 26.3 nautical miles above the Earths surface.