Insulating foam that covers brackets of Discovery's external fuel tank needs to be removed before the shuttle can fly again, NASA said Friday.
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.