Discovery’s Early February Launch Opportunity Delayed as Work Continues on External Tank

The Space Shuttle Program held its weekly Program Requirements Control Board (PRCB) meeting today to review progress on the continuing engineering investigation, testing and analysis regarding shuttle Discovery’s external fuel tank stringer crack issue. With the work remaining, the potential for additional modifications yet to be defined, and further reviews pending, the decision was made today to allow the teams additional time and delay the next launch opportunity out of the early February launch window, which opened Feb. 3. New potential launch dates for Discovery’s STS-133 mission and shuttle Endeavour’s STS-134 mission will be discussed at next Thursday’s PRCB meeting.

Progress continues to be made in understanding the most probable cause of cracks discovered on Discovery’s external tank mid-section, known as the intertank, where small cracks developed during the Nov. 5, 2010, launch attempt. Four additional small cracks were found during thorough X-ray image scans of the backside of the tank after Discovery was returned from the launch pad to the Vehicle Assembly Building at NASA’s Kennedy Space Center in Florida on Dec. 22.

Plans are for the repair work to continue through the weekend. The shuttle program also reviewed the plan to modify as many as 32 additional stringers with radius blocks, which will provide added structural support in areas known to carry much of the structural load of the external tank. These radius blocks essentially fit over existing stringer edges through which the securing rivets are installed to provide additional structural support. The radius block modification is a known and practiced structural augmentation technique used extensively on the intertank. This work should begin as soon as the repairs to the three stringers with the four additional small cracks have been completed, likely in the next day or so, and the modification of the additional 32 stringers is expected to be complete next week.

Senior NASA managers and Space Shuttle Program managers will meet Monday to review the progress to date and the forward plan. A determination of the need and viability for the installation of additional radius blocks on all remaining stringers will be made sometime next week.