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KENNEDY SPACE CENTER, FLA. - After rollback of the rotating service structure (RSS) on Launch Pad 39B, Space Shuttle Discovery stands bathed in lights from the RSS and fixed service structure. The rollback was in preparation for launch July 1 on mission STS-121. Extending toward the cockpit of the shuttle is the orbiter access arm with the White Room extended. The White Room provides access into the orbiter for the astronauts. The RSS provides protected access to the orbiter for changeout and servicing of payloads at the pad. The structure is supported by a rotating bridge that pivots about a vertical axis on the west side of the pad's flame trench. The hinge column rests on the pad surface and is braced to the fixed service structure. Support for the outer end of the bridge is provided by two eight-wheel, motor-driven trucks that move along circular twin rails installed flush with the pad surface. The track crosses the flame trench on a permanent bridge. The RSS is 102 feet long, 50 feet wide and 130 feet high. The structure has orbiter access platforms at five levels to provide access to the payload bay while the orbiter is being serviced in the RSS. Each platform has independent extendable planks that can be arranged to conform to a payload's configuration. This mission is the 115th shuttle flight and the 18th U.S. flight to the International Space Station. Photo credit: NASA/Kim Shiflett