Investigators probing the U.S. space shuttle Columbia disaster are piecing together the world's biggest puzzle. In a big U.S. space agency hangar in Florida, workers are painstakingly placing thousands of recovered shuttle parts in their original position and analyzing each for clues to what caused the orbiter to disintegrate upon re-entry last month.
The floor of the huge hanger is taped with a grid. Overlaying it is an outline of a U.S. space shuttle. About 300 technicians and engineers in white laboratory coats, gloves, and goggles work in two shifts labeling and assembling shuttle Columbia debris in their proper relative positions in the squares.
The workers face an enormous and intricate task. More than 22,000 pieces of the shuttle have been recovered from Texas and neighboring Louisiana, where it broke up during its searing atmospheric re-entry. The debris arrives each day on long flatbed and trailer trucks.
While the hangar team arranges the parts, experts analyze the condition they are in for clues to the cause of the accident. Based on temperature readings relayed by shuttle sensors to ground controllers minutes before the disaster, the independent board of specialists investigating the accident believes atmospheric gases, superheated by re-entry friction, entered an opening in the left wing and caused structural havoc.
The theory is supported by black metal residue on some thermal tiles and inside the left wing's leading edge. According to board member Roger Tetrault, it indicates that the penetrating gases melted some of the orbiter's aluminum and steel structure.
"Many of the tiles on the left side have a thick black deposit on them, and that deposit has never been seen on any previous flight," he said. "We see the black deposits on the right side as well, which means you had molten aluminum being sprayed or deposited onto those tiles on the right side where the event was not occurring. That's a very hot re-entry."
The main question investigators seek to answer is where on the left wing the hot gas penetrated. Mr. Tetrault and his colleagues believe that location will signal the cause of the disaster. As a result, they are most interested in debris with the worst heat damage.
"What we have to do is follow the heat. We will be doing this in order to back into the location of the original breach in the wing," explained Mr. Tetrault.
But the board says that its job is just beginning. The 22,000 pieces of shuttle debris recovered represent just 14 percent of the orbiter by weight. Only 70 percent of the pieces have been identified. The experts say most parts might never be found because they probably burned up in the atmosphere after breaking off the shuttle.
But investigation board chairman Harold Gehman pointed out that the pieces that are available are being rigorously inspected to determine which side of Columbia they came from.
"Right now, we've got all these random pieces and we're seeing all these marks and chars and destruction," he said. "It will be useful to us when we get an identical piece from the right wing and the left wing and we can see if there is a difference in how they looked."
Seventeen years ago, the team investigating the explosion of the shuttle Challenger had an answer within one month. It is clear that the Columbia probe will take a lot more time. But Mr. Gehman is certain that the answer is waiting to be found among the debris.
"We are still working seven days a week," he said. "We still have confidence that we're going to find the cause the direct cause and determine the contributing causes. We're not getting discouraged just because we haven't found it so far."
Whenever the investigation is finished and shuttles return to flight, the pieces of Columbia scattered on the floor of the U.S. space agency hanger in Florida will go to their final repository, a former missile silo close to a similar resting place for the remains of the shuttle Challenger.