"We have had some e-mail correspondence that potentially looks like it could be either (tiles) or wing material," said Michael Kostelnik, NASA's deputy associate administrator for the shuttle and space station.

"If it is wing material obviously that would be important to the investigation," Kostelnik said at a briefing at US space agency headquarters. "The sources were credible enough to cause us to send a NASA team out to take a look."

While the search for debris from Saturday's fatal break-up of Columbia continued over a wide swath of Texas and Louisiana, Kostelnik said material from early in the event would be most helpful to the investigation.

"Certainly early debris, early in the flight path, would be critical because that material would obviously be near the start of the event, so it would clearly be very important to see material earliest in the sequence," he said.

In addition, Kostelnik said an Apache helicopter in the area as the shuttle streaked down over the southwestern United States had captured pictures of the shuttle, and NASA was analyzing those images.

Most of the investigative team probing the disaster took a break from work on Tuesday in deference to a memorial service for the seven astronauts killed.

NASA is still interested in a large piece of foam insulation that fell off Columbia's external fuel tank some 80 seconds after launch and appeared to hit the underside of the shuttle under the left wing.

Space agency engineers analyzed possible impact from the foam, but reported on the mission's 12th day that it would likely cause only localized structural damage and had not endangered the safety of the flight.

Taking Refuge at Space Station?

NASA has been closely questioned on possible rescue strategies for the crew in the event engineers had deemed the incident too risky to continue, especially the possibility of sending the shuttle crew to the orbiting International Space Station.

Columbia, the oldest space shuttle, was too heavy to easily be boosted to the station's orbiting height of about 240 miles (386.2 km). The other three remaining shuttles can dock with the station.

"I think in hindsight that's probably a good thought," Kostelnik said when asked about this possibility.

Asked further about the apparent lack of escape or rescue strategies or backup plans for the Columbia crew, Kostelnik said, "I believe the best response to that would be to talk about the incredible degrees we go to get everything right to make sure there is redundancy in every activity ... There are not a lot of margins on some of these activities."

Near Nacogdoches, Texas, the chairman of the independent investigation board into the disaster visited some of 3,500-odd sites where debris rained down on Saturday in the worst US space accident since Challenger blew up in 1986.

After viewing broken and burned parts from the shattered spacecraft, Chairman Harold Gehman vowed to get to the bottom of what caused it to fall apart.

"Our first imperative is to get it right. The astronauts who will fly in future orbiter missions need to know that we have done everything we possibly can to come to the bottom of this and fix it," said Gehman, a retired Navy admiral who headed a probe of the suicide bombing of the destroyer USS Cole in Yemen.

In Florida, north of the Kennedy Space Center's twin shuttle launch pads, park rangers scoured Playalinda Beach for any debris that may have fallen from Columbia on takeoff.

Bob Newkirk, superintendent of the Canaveral National Seashore, said the sparsely developed beach had been closed since Saturday and would probably reopen on Tuesday, as the search wrapped up.

Unlike the Texas debris field, anything discovered in Florida would have been on the thin strip of beach since Jan. 16 without having washed out to sea. Anything landing in the ocean could take weeks to come ashore, or could be swept off by the Gulf Stream current, headed for the North Atlantic.

(China Daily February 5, 2003)