32 Stringers Undergoing Modifications

Science technicians at NASA’s Kennedy Space Center in Florida now are modifying 32 support beams, called stringers, on space shuttle Discovery’s external fuel tank instead of 34. Teams have determined that modifications on two stringers are not needed because one stringer already is being repaired due to cracks found on Dec. 29 and the other is made with a stronger type of aluminum. Crews will fit pieces of metal, called radius blocks, over both edges of the stringers where they attach to the external tank’s thrust panel area. The radius blocks will increase the structural support of the stringers. The thrust panel areas are located at the attachment points between the tank and the solid rocket boosters, which see the most stress during the flight into orbit. The work is expected to be completed by the end of next week.

‪Repairs to four cracks on three stringers on the opposite side of the tank from Discovery that were discovered Dec. 29 began Monday and are expected to be completed by Friday. Technicians removed the stringers overnight and begin installing replacement stringer sections today. The repairs are similar to repairs made on cracks found on two stringers after Discovery's Nov. 5 launch attempt.

‪Teams also are performing scans on all of the tank’s stringers using a backscatter device, which bounces radiation off the tank allowing engineers to see below the foam insulation. Engineers at various NASA centers continue to analyze testing and imaging data. Preliminary results from this latest round of X-ray type image scans show no cracks in the stringers that have been scanned so far. Managers will meet again Thursday to determine whether radius block modifications are needed on the remaining stringers. Scans are expected to be completed this weekend.

‪‪The next available launch date for Discovery's STS-133 mission to the International Space Station remains Feb. 3 at the opening of a window that extends through Feb. 10.