Following an extensive investigation into the cause of tiny cracks inside fuel lines of the four space shuttle orbiters, NASA today announced the team is ready to resume preparations for launching on Sept. 28, with Atlantis up first on an assembly mission to the International Space Station (ISS).

"We’ve just completed a thorough review of the team’s findings and recommendations, and I am pleased to report to you that — pending the satisfactory completion of welding repairs — we plan to resume shuttle flights by the end of September," said Ron Dittemore, NASA Space Shuttle Program Manager, Johnson Space Center, Houston. "There always will be inherent risks in space flight and it’s our job to manage those risks appropriately."

A welding and polishing process is being implemented that will restore flow-liner integrity to design condition. These liners are inside the space shuttle Main Propulsion System fuel lines to preclude liquid hydrogen and oxygen turbulent flow into the engines during launch and climb to orbit.

The technique calls for welds of three very small cracks on Atlantis and two on Endeavour, which now is targeted for a launch no earlier than Nov. 2, also to the ISS. Additionally, the microscopic rough edges of the liner holes will be smoothed by polishing to reduce the chance of more cracks developing in the future.

These two ISS assembly missions (STS-112/9A and STS-113/11A) will deliver additional segments for the station’s eventual 360-foot-long truss structure. STS-113 will serve as an ISS crew-rotation mission as well.

Columbia’s 16-day dedicated research mission (STS-107) is targeted for no earlier than Nov. 29, pending further review.

The welding repair was chosen after several groups of engineers determined the most likely cause of these cracks is high-cycle fatigue — a phenomenon attributed to combined environments such as vibration, thermal and acoustics.

Space shuttle flights have been on hold while teams of engineers evaluated, from a safety-of-flight standpoint, the cause of these tiny cracks discovered in June.