Retired Navy Adm. Harold Gehman Jr. called the unsolicited tips "serious communications."

"These are not crackpot kinds of things," Gehman told The Associated Press.

Gehman and the other members of the panel Thursday spent their second day at the Kennedy Space Center visiting a hangar where the Columbia debris eventually will be assembled and learning about how the space shuttles are refurbished and launched.

Since the investigation began last week, the board has received 12 to 20 unsolicited tips from former NASA workers and academics who follow the space program. Each tip is being cataloged and will be followed up, Gehman said.

The tips deal with such subjects as the material used to build the shuttle and the operation of the spacecraft, Gehman said.

"I have unsolicited letters from engineers. I have pieces of evidence that people are mailing in," Gehman said. "We're quite aware that in the case of Challenger, there were very interesting things that came from unsolicited sources, and we're taking them very seriously."

Gehman would not say whether any tips had come from current NASA employees.

An independent panel also investigated the Challenger explosion in 1986.

The Columbia investigative board has set up a mailing address and Web site separate from NASA so more people can come forward with information. The addresses were not immediately available.

The board is in the fact-finding stage of its investigation. Board members are learning about shuttle operations, procedures and manufacturing from top managers and line workers, Gehman said.

When board members move into the second stage of the investigation, Gehman said, workers will be able to give sworn statements and will receive protection if necessary.

"During the investigatory phase, witnesses are protected," he said.

--From the Friday, February 14, 2003 online edition of the Augusta Chronicle