NASA fuels shuttle tank for sixth launch try

CAPE CANAVERAL, Florida — The fueling of shuttle Endeavour's external tank is in the fast-fill stage now and engineers are not working any technical issues as NASA presses ahead with a sixth attempt to launch its next International Space Station assembly mission.

Liftoff remains targeted for 6:03 p.m. ET and the weather forecast is favorable. Meteorologists say there is a 60% chance NASA will be able to get Endeavour and seven astronauts on their way to the station with the third and final segment of the Japanese Kibo science research facility.

"Kibo" means "hope" in Japanese, and mission managers are hoping seasonal thunderstorms skirt the area around the nation's shuttle homeport during a 10-minute window that will open at 5:58 p.m. ET.

NASA targets the middle of the window to optimize propulsive power during the nine-minute climb into orbit.

NASA engineers started fueling Endeavour's external tank at 8:38 a.m. ET. The three-hour operation begins with a "slow-fill" phase during which propellant lines are chilled down to condition them for cryogenic temperatures.

An 850,000-gallon sphere at launch pad 39A holds liquid hydrogen at temperatures of Minus 423 degrees Fahrenheit. A 900,000-gallon sphere holds liquid oxygen -- which is Minus 298 degrees Fahrenheit -- on the other side of the oceanside launch complex.

The propellants flow through ground support lines and the mobile launcher platform before coursing through shuttle orbiter main propulsion system lines and finally into separate reservoirs within the external tank.

Engineers began the "fast-fill" phase of fueling operations right around 9:30 a.m. ET.

The tank should reach the 98% full level between 10:45 a.m. and 11 a.m. It is at that point gaseous hydrogen leaks cropped up, triggering June 13 and June 17 launch scrubs.

NASA subsequently repaired a leaky gaseous hydrogen vent line assembly and no significant leaks were detected during fueling operations Sunday and Monday. A launch attempt Saturday was scrubbed prior to propellant-loading operations to give engineers more time to analyze Friday night lightning strikes at the launch pad.