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

Engineers pinpointed the source of a launch-delaying oxygen leak today, cut out a damaged section of metal-sheathed flex hose and inserted a replacement segment to complete a tricky repair job aboard the space shuttle Endeavour.

Still unresolved is the status of Endeavour's 50-foot robot arm, which was hit by an access platform Tuesday during work to gain access to the leaking oxygen line. The cargo access platform, or CAP, scraped and dented a section of the arm's protective honeycomb shell and engineers are still trying to determine whether the arm suffered any more serious damage.

The Canadian-built robot arm is crucial to Endeavour's mission to attach a 14.5-ton solar array truss segment to the international space station. Because of clearance issues, the station's Canadarm2 space crane cannot lift the P1 truss from the shuttle's cargo bay. Endeavour's initial extraction must be accomplished by the shuttle's robot arm, which eventually will hand the truss off to the station arm for installation.

After removing protective insulation, engineers plan to use ultrasound Thursday to assess the integrity of the composite structure of the shuttle arm. A loads analysis also is underway to analytically determine what sort of forces the arm might have been subjected to when it was hit, or nudged, by the CAP. Officials say mission managers will meet Friday afternoon to assess the oxygen line repair and the status of the robot arm troubleshooting.

Technicians work on Endeavour's payload bay floor to access the leak. Photo: NASA TV/Spaceflight Now

The oxygen leak, discovered last Sunday evening a few hours before a planned early Monday launch, forced NASA managers to put the flight on hold. At the time, shuttle program manager Ronald Dittemore said if the leak repair work went smoothly, Endeavour could be ready for a second launch attempt this Monday night, between 7 p.m. and 11 p.m. But the robot arm damage is a wild card and it's not yet clear what impact, if any, the incident might have on Endeavour's eventual launch date.

Another wild card is Boeing's first Delta 4 rocket, a heavy-lift unmanned booster scheduled for its maiden launch Saturday from the Cape Canaveral Air Force Station. Forecasters are predicting bad weather Saturday and the owners of the European communications satellite being launched by the new rocket have ruled out launch attempts Sunday or Monday because of the Leonids meteor shower.

If the forecast doesn't improve - and as of this writing, that appears unlikely - Boeing could elect to forego a Saturday launch attempt and instead retarget for Tuesday. But all rockets launched from Florida, manned or unmanned, rely Air Force Eastern Range tracking radar and other equipment and it typically takes a full day to reconfigure the range to support a different launch.

New rockets like the Delta 4 typically get three days on the range. As of this writing, Monday is strictly a target for Endeavour; NASA has not yet formally requested a launch date from the Eastern Range. If Boeing ultimately gives up on Saturday and gets range support for Tuesday, Endeavour could be delayed to Wednesday.

But at this point, the Delta 4 remains scheduled for launch this Saturday and Engineers remain hopeful Endeavour will be ready to go by Monday. Stay tuned!

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