KSC-08pd1502

CAPE CANAVERAL, Fla. -- On Launch Pad 39A at NASA's Kennedy Space Center, the rotating service structure, or RSS, has rolled back on its axis to uncover space shuttle Discovery, lighted against the night sky, in preparation for launch on the STS-124 mission. Support for the outer end of the bridge is provided by two eight-wheel, motor-driven trucks (one is seen at bottom left) that move along circular twin rails installed flush with the pad surface. First motion was at 8:33 p.m. and rollback was complete at 9:07 p.m. The structure provides protected access to the shuttle for changeout and servicing of payloads at the pad. It is supported by a rotating bridge that pivots on a vertical axis on the west side of the pad's flame trench. After the RSS is rolled back, the orbiter is ready for fuel cell activation and external tank cryogenic propellant loading operations. The pad is cleared to the perimeter gate for operations to fill the external tank with about 500,000 gallons of cryogenic propellants used by the shuttle’s main engines. This is done at the pad approximately eight hours before the scheduled launch. Above the orange external tank is the oxygen vent hood, called the "beanie cap," at the end of the gaseous oxygen vent arm extending from the fixed service structure. Vapors are created as the liquid oxygen in the external tank boil off. The hood vents the gaseous oxygen vapors away from the space shuttle vehicle. Below is the orbiter access arm with the White Room at the end, flush against the shuttle. The White Room provides access into the shuttle. The STS-124 mission is the second of three flights launching components to complete the Japan Aerospace Exploration Agency's Kibo laboratory. The shuttle crew will install Kibo's large Japanese Pressurized Module and its remote manipulator system, or RMS. The 14-day flight includes three spacewalks. Launch is scheduled for 5:02 p.m. May 31. Photo credit: NASA/Troy Cryder