Engineers working in the shuttle Endeavour's cargo bay at launch pad 39A have found what they believe is the oxygen leak that grounded the ship earlier this week. The leak, which one official said was audible, is believed to be in a flex hose assembly near a dynatube fitting at the forward bulkhead of the shuttle's cargo bay. There are no visible signs of damage, but engineers are preparing for work to remove and replace the suspect section of tubing.

Engineers are still assessing what to do, if anything, about a gaseous nitrogen line that is structurally connected to the suspect oxygen line. Replacing the GN2 line would require additional work just to gain access and no decision has been made yet about how to proceed in that regard.

Likewise, engineers are still assessing possible damage to Endeavour's robot arm. A cargo access platform extended into the payload bay Tuesday for the oxygen line work inadvertently hit the fragile crane, ripping its protective thermal insulation just about its shoulder joint. It's not yet known if the arm suffered any more serious damage.

The 50-foot-long robot arm is crucial to Endeavour's mission to deliver and install a new solar array truss segment on the international space station. Troubleshooting possible arm damage is a challenge because the crane, which cannot support its own weight in Earth's gravity, cannot be moved at all when the shuttle is vertical on the launch pad. Beyond electrical continuity checks and visual inspections, it's not yet known what options are available for testing.

The oxygen leak and arm issues will be discussed later today by senior NASA managers. NASA continues to hold out hope Endeavour can be ready for launch by Monday, but that assumes no major arm repairs are required and that the oxygen leak repair work goes smoothly.