The space shuttle Columbia almost certainly suffered a devastating breach of its skin, allowing superheated air inside the left wing and possibly the wheel compartment during its fiery descent, investigators said Thursday.
In its first significant determination, the accident investigation board announced that heat damage from a missing tile would not be sufficient to cause the unusual temperature increases detected inside Columbia minutes before it disintegrated. Sensors noticed an unusual heat buildup of about 30 degrees inside the wheel well before the accident.
Instead, the board determined those increases were caused by the presence inside Columbia of plasma, or superheated air with temperatures of roughly 2,000 degrees. It said investigators were studying where a breach might have occurred to allow plasma to seep inside the wheel compartment or elsewhere in Columbia's left wing.
The board investigating the Columbia disaster has received unsolicited letters and documents from former NASA workers and others offering tips on why the shuttle may have disintegrated, the panel's chairman said Thursday.
Retired Navy Adm. Harold Gehman Jr. called the tips "serious communications."
"These are not crackpot kinds of things," Gehman told The Associated Press.
Meanwhile, NASA officials said the remains of all seven Columbia astronauts have been positively identified and the search for additional remains has ended. The identifications were made at the mortuary at Dover Air Force Base, where the remains were taken after the space shuttle disintegrated Feb. 1.
On Wednesday, law enforcement officials said search crews in East Texas had found "significant amounts" of human remains.
"We are comforted by the knowledge we have brought our seven friends home," Bob Cabana of the Johnson Space Center in Houston said in a statement. "We are deeply indebted to the communities and volunteers who made this homecoming possible, and brought peace of mind to the crew's families, and the entire NASA family."
The remains of Israeli astronaut Ilan Ramon were returned to his homeland earlier this week. As for the other astronauts, "we are working toward releasing the crew remains to the families for their own private memorial services," said Johnson Space Center spokeswoman Eileen Hawley.
Gehman and the other members of the panel Thursday spent their second day at the Kennedy Space Center in Cape Canaveral visiting a hangar where the Columbia debris eventually will be assembled and learning about how the shuttles are refurbished and launched.
Since the investigation began last week, the board has received 13 to 19 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.