Two cracks have been discovered on the space shuttle Discovery's external fuel tank, presenting further issues for the orbiter's planned final launch.

Technicians began repair work on Discovery this morning (Nov. 10), and identified the cracks on the aluminum body of the tank. An earlier crack had been discovered in the insulating foam layer that coats the tank.

After a series of delays and glitches prevented the orbiter from launching last week, NASA is aiming to lift off Discovery on a mission to the International Space Station no earlier than Nov. 30.

NASA officials are evaluating images of the cracks to determine how to repair them as the orbiter sits on its launch pad at NASA's Kennedy Space Center in Florida.

"This is still really early on, so the exact repair method and schedule is still being figured out," NASA spokesman Allard Beutel told SPACE.com. "It's just a matter of the repair method and how best to go about it. Right now, we're looking at repair options that can be done at the pad."

Shuttle technicians have repaired similar cracks on external tanks by removing the fractured aluminum and replacing it with a twice-as-thick stringer section, before replacing the foam. But, these repairs have previously only been executed during the external tank production phase.

"We've seen these kinds of things before at the tops of stringers," Beutel said. "They've done repairs to them before, but we've never done them here at Kennedy. They were always done at Michoud."

NASA's Michoud Assembly Facility, located in New Orleans, La., manufactures and assembles critical hardware components for the space shuttles, including the massive orange external tanks.

The new cracks were found when engineers removed the external tank's foam insulation, revealing two fractures about 9 inches (23 centimeters) long on a section of the tank's metal exterior called the stringer, which is the composite aluminum ring located on the top of the intertank area. [GRAPHIC: NASA's Space Shuttle – From Top to Bottom]

"The cracks were discovered in the area underneath the foam that was dissected and removed," Beutel said. "Given where the foam insulation crack was, and how it happened, the team actually suspected they would find other things once they got in there."

The damage to the foam insulation of Discovery's external tank was initially spotted during an inspection following the shuttle's canceled launch attempt last week. The crack in the foam insulation was estimated to be 20 inches (51 cm) long.

NASA officials are still determining the root cause for the tank damage, but have stated that the two cracks discovered today occurred during operations to drain the tank of its cryogenic propellant, following the most recent launch attempt on Nov. 5.

Meanwhile, engineers are also continuing work on a separate issue on Discovery's external fuel tank – a component called the ground umbilical carrier plate (GUCP), where a hydrogen gas leak was discovered last week.

Discovery's STS-133 mission managers are evaluating the data to determine the schedule of repairs and the next possible launch opportunity for the orbiter.

After Discovery's final flight, NASA plans to retire the shuttle — along with the rest of the agency's shuttle fleet — in 2011.

The next possible time that Discovery can attempt a liftoff to the International Space Station is Nov. 30 at 4:02 a.m. EST (0902 GMT). Discovery is scheduled for an 11-day supply mission to the space station to deliver a humanoid robot helper for the station crew and a new storage room for the orbiting lab.

This article was reprinted with permission from SPACE.com.

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