A worker holds the leaky oxygen hose that scrubbed Endeavour's launch. Photo: NASA TV/Spaceflight Now

The leaking oxygen line that grounded the shuttle Endeavour last Sunday evening may have failed because of structural fatigue, engineers said today, raising the possibility of a fleet-wide issue. Technicians have been asked to examine oxygen and nitrogen lines in the shuttle Discovery overnight to determine if any obvious problems are present on that vehicle.

The lines in question are metal-sheathed flex hoses used to carry oxygen and nitrogen from supplies under the payload bay into the shuttle's crew cabin. Two independent oxygen lines feed through the crew cabin's aft bulkhead and one of them was found to be leaking during Endeavour's countdown Sunday night. Launch, which had been targeted for 12:59 a.m. Monday, was called off.

Engineers quickly found the leak and the suspect section of oxygen line was cut out and replaced Wednesday. An associated nitrogen line that is coupled to the same support fittings was not touched.

The section of leaking oxygen line then was subjected to a detailed inspection and, contrary to expectations, no signs of inadvertent damage were found. Instead, the leading theory for want went wrong is "fatigue related failure," a NASA official said today. To find out if such fatigue is age related and thus a possible fleet-wide problem, engineers are examining similar oxygen and nitrogen lines aboard Discovery.

Such flex hoses are used in several areas of the shuttle's life support and main propulsion systems. There are no indications any other shuttles have fatigue-related problems, but NASA managers want to make sure.

In the meantime, engineers have removed damaged insulation from Endeavour's robot arm and are preparing to use ultrasound equipment overnight to make sure the underlying structure is sound. The arm was dinged Tuesday when an access platform needed for the oxygen line repair work inadvertently hit the crane's shoulder section during insertion into Endeavour's payload bay.

NASA managers will be briefed on the arm inspections, and the latest on the oxygen line issue, at a meeting late Friday afternoon. If both issues can be resolved by then, Endeavour could, in theory, be cleared for a second launch attempt Monday night. But the maiden launch of a commercial Boeing Delta 4 rocket, currently scheduled for Saturday afternoon, likely will cause problems for NASA.

The forecast Saturday calls for an 80 percent chance of bad weather. A launch is not possible Sunday or Monday because the owner of the satellite aboard the Delta 4 does not want to launch at the height of the Leonids meteor shower. Depending on the forecast, Boeing managers could opt to bypass a Saturday launch attempt and to shoot instead for launch tries Tuesday and Wednesday.

Under that scenario, the earliest the shuttle could launch would be Thursday because it now takes 48 hours to reconfigure Air Force tracking systems used to support all East Coast rocket launchings. On the other hand, Boeing could take a shot at launching Saturday and, if NASA has not resolved the shuttle issues by then, try again on Tuesday anyway.

All of this is pure speculation at this point. But - shuttle problems aside - it would appear Boeing is in the driver's seat when it comes to setting the near-term launch schedule.

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