Shuttle Fuel Leak Appears To Be Fixed
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By Frank Morring Jr.
Space shuttle managers will try again to launch Endeavour July 11, after repairs to a troublesome gaseous hydrogen leak apparently worked during a full-scale fueling test July 1.
Crews at Kennedy Space Center (KSC) filled Endeavour's huge external tank with liquid hydrogen and liquid oxygen in the morning to check a seal at the ground umbilical carrier plate, where gaseous hydrogen boiling off from its supercold liquid state is vented into the launch pad for safe burnoff. The seal, beefed up with a spring for a tighter fit, and the realigned carrier plate performed as hoped, releasing only 12 parts per million of gaseous hydrogen.
"The liquid hydrogen level has reached stable replenish, and teams have not detected any leaks," said NASA launch commentator Candrea Thomas as the hydrogen tank reached the point where fresh liquid hydrogen was being pumped in to replace that lost to boiloff.
Leaks in the 60,000-parts-per-million range at that point in the tanking process forced NASA to scrub two earlier attempts to send Endeavour on its way to the International Space Station (ISS). Those scrubs - on June 13 and June 17 - followed an earlier scrub on the STS-119 mission in March for a leak that cleared up for a later launch.
Mike Moses, shuttle launch integration manager, said the successful tanking test paves the way for another launch attempt at 7:39 p.m. EDT July 11. Endeavour and the STS-127 crew had to stand down after the second June attempt because solar angles at the ISS prevented acceptable thermal conditions for the planned 11-day portion of the mission that the orbiter would have spent docked to the station.
Still to be determined is the root cause of the problem, which Moses said grew out of a misalignment of the connecting hardware. To get a good seal for the tanking test, engineers carefully measured the concentricity of the parts, installed new pivot "feet" on the umbilical plate to correct the misalignment and then used the spring-loaded Teflon gasket as "insurance" that the other repairs would work.
While thermal conditions at the space station will permit docking there well into the fall, Endeavour faces a range conflict on July 17 that may have to be negotiated if the launch date slips, Moses said. The next shuttle mission - STS-128 on Discovery - might have to move back a day or two from its Aug. 18 launch date to accommodate a delay in STS-127, Moses said.
Timing for the mission after that is less certain. The shuttle Atlantis is scheduled to launch to the ISS on Nov. 12 with a load of supplies, but a problem discovered after Atlantis visited the Hubble Space Telescope in May could force that flight into December.
During the STS-125 Hubble servicing mission a small knob floated into a tight space next to one of the cabin windows and got wedged there. While the knob has been recovered, engineers are worried that it may have caused structural damage to the window pane.
Tests and analysis are ongoing to determine whether that is the case. If it is, Moses said, it could take as long as two months to replace the window and another two months to test it. The job, which would involve removing a bank of switches and then reinstalling and testing the circuitry, was last performed at the shuttle assembly and overhaul facility in Palmdale, Calif., which has been closed. It has never been done at KSC, he said.
Endeavour photo: NASA
