NASA shuttle program managers on Thursday ordered additional repairs to new cracks found on shuttle Discovery’s external fuel tank.
Discovery’s 39th and final mission, an 11-day assembly flight to the International Space Station, has been on hold since a Nov. 5 launch scrub.
In the aftermath of the launch delay, technicians found four small cracks in two neighboring 21-foot-long metal support stringers on the shuttle’s 154-foot long fuel tank. The initial cracks were repaired, and shuttle managers ordered a Dec. 17 launch pad tanking test at the Kennedy Space Center to help determine the cause of the damage.
Following the test, Discovery was transported to Kennedy’s Vehicle Assembly Building for a detailed X-ray analysis of the tank’s stringer section — a distinct ribbed region that separates internal hydrogen and oxygen propellant containers. Each tank has 108 of the support stringers.
Four new crackswere discovered late Wednesday, the space agency said. The initial cracks were found on a section of the circular tank facing Discovery. The latest cracks were found on a section facing away from the orbiter.
The stringer cracks could lead to separations in the insulating foam that covers the tank. Pieces of damaged foam could break away in flight and strike the shuttle’s fragile heat shielding.
During a previously scheduled meeting on Thursday, shuttle managers called for repairs to the newly discovered cracks. However, they deferred a decision on modifying the tank with structural doublers on regions that experience the highest stresses during the launch. More analysis is continuing as shuttle managers attempt to determine whether the cracks were caused by material defects, a mis-assembly issue or perhaps during some phase of launch processing.
The next launch window extends from Feb. 3 to 10.
Discovery’s six astronauts have trained to equip the space station with an equipment stowage module and an external platform to hold spare parts.
The Nov. 5 scrub was caused by an unrelated hydrogen leak, which has since been repaired.
The space agency plans to retire the shuttle fleet in 2011, after two and possibly three more missions.