NASA managers have narrowed down the problem to the Aft Load Control Assembly #2 (LCA 2) and in particular they believe the problem is with failed Hybrid Load Drivers within the LCA. The LCA is located in Endeavour's aft avionics bay 5. They will pull out the LCA tomorrow and install a spare on Tuesday. It will take 2 days of testing before they can consider proceeding with a new countdown for a no earlier launch day of Sunday, May 8th, Mother's Day.
Photo Provided by Ken Kremer
However the timeline is extremely tight to make a May 8th launch window. For that to happen engineers would have to start testing the spare LCS on Tuesday morning to resume a countdown on Thursday morning. If they can't launch on Sunday the 8th then NASA is currently unsure if they can launch on the 9th due to a conflict with a Russian Soyuz undocking from the space station while Endeavour is at the International Space Station at the end of its mission. Beyond the 9th NASA has no conflicts should it want to launch between the 10th and the end of that week on the 15th.
This is not the first time NASA has had to remove and replace a Load Control Assembly and so they are familiar with the procedure to test the replaced box. At the same time engineers will be checking the LCA they removed to confirm what exactly within the box caused the problem so they fully understand the issue.
If Endeavour can be launched by May 10th it should have no impact on the targeted date of June 28th for the final shuttle launch of Atlantis. However if Endeavour's launch slips further it could impact the Atlantis launch date.
You can follow updates as they happen on our Twitter accounts @SpaceRef, @NASAWatch and for Marc Boucher @00mb.