NASA may push back plans to launch its next shuttle mission until March 2006, allowing engineers more time to solve an ongoing foam shedding problem with orbiter external tanks.

A September launch attempt of the space shuttle Atlantis and its STS-121 mission - NASA's second orbiter to fly since the Columbia disaster - is all but out, with space agency officials stating last week that chances were slim they would make the four-day window that opens on Sept. 22.

Shuttle managers are discussing whether to push past a brief, four-day launch window in November, and even switch shuttles - launching Discovery instead of Atlantis - for the next orbiter flight, NASA officials said.

"There have indeed been discussions about that," NASA spokesman Allard Beutel told, adding that an update on NASA's shuttle program status is set for 12:00 p.m. EDT (1600 GMT) today.

Shuttle officials have pledged not to launch the next shuttle mission until the foam issue is solved.

A large piece of foam insulation weighing nearly one pound pulled free from the external tank fueling the space shuttle Discovery about two minutes into its July 26 launch. The foam missed the orbiter, but was the largest of several pieces of foam debris that exceeded safety restrictions put in place after the Columbia accident.

Columbia broke apart during reentry on Feb. 1, 2003, when damage caused at launch by the impact of a 1.67-pound piece of tank foam debris allowed hot atmospheric gases to enter the resulting hole and rip apart the shuttle. Its seven-astronaut crew did not survive.

Preparations are underway to send an external tank from NASA's Kennedy Space Center spaceport in Cape Canaveral, Florida back to Michoud Assembly Facility in New Orleans, Louisiana - where the tanks are built - so engineers can begin troubleshooting efforts.

Beutel said that shuttle managers were still discussing whether to pry Atlantis from its external tank to allow the fuel container to be shipped back to Michoud, or whether a separate tank at KSC will be sent back.

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