Confident shuttle fuel line cracks can be fixed, if necessary, by welding, NASA managers are converging on a plan to resume shuttle launches in late September or early October with the first of two back-to-back space station assembly missions. Under that preferred scenario, launch of the shuttle Columbia, originally scheduled for July 19, would slip to around Dec. 3.

Shuttle program manager Ronald Dittemore today stressed the plan is strictly "preliminary" at this point and that a final program review is planned for July 31. But as of today, it appears NASA will opt to fix the fuel line flow liner cracks found in all four space shuttles using a straight-forward welding technique and that Atlantis will be first off the pad at some point after Sept. 26. The goal of that mission - station assembly flight 9A - is to attach the first starboard solar array truss segment to the international space station.

The shuttle Endeavour then would follow suit Nov. 2 on assembly flight 11A to deliver the first port-side truss segment, to ferry a fresh three-person crew to the orbital lab complex and to bring the station's current occupants back to Earth. Under this scenario, NASA would close out the year by launching Columbia on a flight featuring the first Israeli astronaut.

The shuttle fleet was grounded earlier this summer after engineers discovered tiny cracks in an internal fuel line baffle just upstream of main engine No. 1 aboard the shuttle Atlantis. Similar cracks then were found aboard Discovery and then Columbia, at which point Dittemore stopped processing for Columbia's planned July flight. Cracks later were found in flow liners aboard Endeavour.

The concern is that if a crack worsened, a piece of debris could break off and get sucked into a main engine with possibly catastrophic results. But the cracks do not appear to be age related and whatever growth they have experienced since first forming has been minimal.

But Dittemore said engineers still don't know what caused the cracks to form in the first place. Even so, he said NASA can safely resume shuttle flights based on the results of extensive testing and analysis.

"We're still searching for that elusive root cause," he said. "But that's not going to hold us up from returning to flight."

Dittemore has not yet ruled out the possibility of resuming shuttle flights without implementing any repairs. But he said today the proposed welding repair is relatively straight forward, easy to carry out and, as of this writing, it is the favored option. He said the cracks in Atlantis' flow liner could be repaired in time to re-install the ship's main engines the last week of August to support a late-September liftoff.