(CNN) -- Insulating foam that covers brackets of Discovery's external fuel tank needs to be removed before the shuttle can fly again, NASA said Friday.
Space shuttle Discovery glides in for landing at Kennedy Space Center on December 22, 2006.
A new X-ray analysis shows small cracks that probably make the material prone to shedding, officials said.
NASA engineers said the foam -- called Super Light-weight Ablative, or SLA -- should be removed from the brackets.
The work will take about nine days and is not expected to delay Discovery's next launch, scheduled for October 23.
Insulating foam covers a shuttle's external tank to prevent ice from building up when super-cold liquid oxygen and hydrogen fuel is pumped into it in the hours before launch.
But foam shedding has been a huge problem for NASA in recent years. The agency has been extremely watchful for any damage to the tank or heat shield after the 2003 Columbia disaster, when a suitcase-size piece of foam flew off the shuttle's external tank and cracked a gash in the leading edge of the left wing.
When the orbiter re-entered the atmosphere to land, searing hot gases seeped into the hole, incinerating the spacecraft and killing the crew of seven.
Two-and-a-half years later, on the first post-Columbia flight, a briefcase-size piece of foam flew off Discovery's tank, narrowly missing the orbiter. The fleet was grounded for another year while engineers designed a fix for that problem.
And just this month, a piece of SLA foam fell off Endeavour's fuel tank 58 seconds after that shuttle's lift-off on August 8, bounced off a strut connecting the shuttle to the tank, and gouged the sensitive heat-resistant tiles on the underside of the orbiter.
After extensive computer modeling and thermal analysis, NASA managers decided the shuttle was safe to return home "as-is," and opted not to send astronauts under the orbiter to try to repair the heat shield.
Endeavour landed safely at Kennedy Space Center in Florida on Tuesday.
In an effort to better understand the root cause of the problem, and prevent it from happening again, shuttle program managers ordered the X-ray tests on Discovery's tank.
The SLA insulation will be removed and replaced with a lighter type of foam.
Next year NASA will debut a tank redesign featuring titanium brackets that will not need to be coated with foam at all. E-mail to a friend 
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