NASA on Monday focused on Columbia's thermal protection system and damage its tiles may have sustained during its launch, as search crews continued their work to recover across east Texas and Louisiana debris and human remains from the space shuttle Columbia.

Engineers are examining the possible effect of a broken-off piece of insulation that hit the left wing of the shuttle during its launch on Jan. 16, according to Bill Readdy, NASA's associate administrator for shuttle and space station and a former shuttle commander himself.

But Readdy and others cautioned that the investigation is still in its early stages and it is far too early to describe the chain of events that led to the second space shuttle disaster. Columbia disintegrated 16 minutes before it was due to land at the Kennedy Space Center in Florida, as family and friends awaited its arrival. The shuttle was on a 16-day science mission. This was its 28th flight since making its first voyage in 1981.

As engineers at the Johnson Space Center in Houston continued to pore over the flight data that Columbia had sent to the ground during its 16-day mission, wreckage was being gathered at Barksdale Air Force Base, near Shreveport, La.

Readdy said an engineering report issued the 12th day of Columbia's flight noted that even if the tiles were damaged, there would be "no burn-through and no safety-of-flight issues." Parts of the shuttle tolerate temperatures as high as 3,000 degrees F when it reenters the Earth's atmosphere. The tiles are designed to protect the shuttle from the heat.

Meanwhile, NASA Administrator Sean O'Keefe announced the members of the Space Shuttle Mishap Interagency Investigation Board, which will provide an independent review of the events surrounding the Shuttle explosion. Retired Admiral Harold W. Gehman, Jr., who co-chaired the independent commission that investigated the attack on the U.S.S. Cole in Aden, Yemen, Oct. 12, 2000, and once served as the commander-in-chief of U.S. Joint Forces Command, will chair the panel. Other members of the investigative board includes:

• Rear Admiral Stephen Turcotte, Commander, U.S. Naval Safety Center, Norfolk, Va.
• Major General John L. Barry, Director, Plans and Programs, Headquarters Air Force Materiel Command, Wright-Patterson Air Force Base, Ohio.
• Major General Kenneth W. Hess, Commander, U.S. Air Force Chief of Safety, Kirtland Air Force Base, N.M.
• Dr. James N. Hallock, Aviation Safety Division Chief, U.S. Department of Transportation, Cambridge, Mass.
• Steven B. Wallace, Director of Accident Investigation, Federal Aviation Administration, Washington.
• Brigadier General Duane Deal, Commander 21st Space Wing, Peterson Air Force Base, Colo.

Separately, Russian space officials said they would put on hold plans to carry tourists to the International Space Station and use their spacecraft only to deliver long-term crews. They also offered to build spacecraft to help compensate for the loss of shuttle flights during the investigation.

Special Report: Columbia Disintegrates