HOUSTON – NASA engineers have concluded that flawed manufacturing caused the fuel-tank insulation failure that forced the most recent a shutdown of the program.

And they hope to have it resolved in time for a launch next May, officials said Friday.

The schedule depends on full reopening of NASA’s New Orleans tank-assembly facility by December. Hurricane Katrina disrupted work at the plant, frustrating hopes to launch by March.

Engineers investigating the loss of insulating foam during launch of Discovery in July – the same problem blamed for the Columbia disaster in 2003 – recently completed an interim report blaming weaknesses in the spray-on process and too much worker contact with the tank, officials said. They’ve recommended corrective measures.

“We have not set an official launch date,” shuttle program manager Wayne Hale said at a news briefing. But, “It appears a May window is something we can work toward.”

The opportunity, governed by the shuttle’s ability to rendezvous with the International Space Station, runs from May 3 through May 23.

NASA’s space shuttles were grounded for 2 1/2 years after flyaway foam damaged Columbia during launch in 2003, causing it to disintegrate over Texas 16 days later as it headed for landing. Seven astronauts were killed. NASA believed the problem was corrected, but more foam flew off when Discovery launched, and the remaining three shuttles were grounded again.

The New Orleans assembly facility escaped serious damage in Katrina, but lost power and water. Power is back on, and a water well has been drilled, Hale said. But many workers lost their homes and roads to the plant were damaged, making getting to work difficult.

Although 500 workers are back on the job, Hale said, NASA needs all 2,000 back by December to have a realistic hope of a May launch.

Richard Gilbrech, head of the investigation team, said causes of the latest insulation failures appear to be a combination of the way it was sprayed on and workers’ accidentally crushing the foam during tank assembly. Workers put mats over the foam to get on it to complete some tasks.

Gilbrech emphasized there was no finding of worker negligence, that the process was the problem. There was more contact with the tank that flew on Discovery because it underwent more changes than normal, officials said.

The investigative team has developed solutions for the five places where foam fell off and has validating tests that appear doable by May, Hale said. He downplayed the schedule slip from March. “We’re all here to report a sense of progress and a great deal of optimism,” he said.

At the same briefing, Bill Gerstenmaier, NASA’s associate administrator for space operations, said plans to cut remaining flights of the shuttle from 28 to 19 before it’s retired in 2010 will mean a smaller International Space Station. The shuttle is necessary to build the station. But he said the resulting station will still be “very viable.”

He also said the reduced shuttle flight manifest still allows a possible mission to repair the Hubble Space Telescope, though no final decision has been made.

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