The problem was traced to one of two positive pressure-relief valves which ensure that the crew cabin does not become over-pressurized, NASA said in a release. Workers plan to remove and replace the suspect valve using a valve from Atlantis.
Endeavour's flight to the International Space Station, will be the first flight for the space shuttle since 2002.
NASA said it is the first mission for Barbara Morgan, a teacher-turned-astronaut whose association with NASA began more than 20 years ago.
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