NASA officials investigating the mid-air disintegration of the Columbiaare claiming a breakthrough after identifying part of the shuttle's left wing.
The wing fragment, found last week, is from the leading edge of the wing, which is made of a reinforced carbon designed to withstand extreme heat.
The discovery may allow investigators establish whether the Columbiafell apart on re-entry to the Earth's atmosphere because a piece of the wing had fallen off or was damaged during take-off.
It was one of 12,000 pieces of the shuttle that have been collected since it broke up over Texas on its homeward flight after 16 days in orbit. All seven astronauts aboard were killed.
The pieces of the shuttle collected since the crash are being stored at a hangar near NASA's Johnson Space Center, and shipment to Kennedy Space Center in Florida will begin today.
NASA chief Mr Sean O'Keefe has denied that critics within the space agency are being muzzled.
Mr O'Keefe was less clear about whether the Russian space agency had been asked to schedule an additional supply flight on the robotic Progressvehicle to the orbiting International Space Station, which holds two Americans and one Russian.
He said the critical item that may run short is water. Normally, about half of the provisions the station requires are brought up by shuttles, he said. Fuel supplies for the station are sufficient for another year, he said.