It was unmistakably NASA technology, like a stubby scale-model Space Shuttle, with black and white protective tiles.

Among the most crucial parts will be the protective ceramic tiles, which NASA officials suspect may have been damaged and contributed to the catastrophic events last Saturday.

Computer programs have failed to show how a piece of foam insulation striking the craft's protective tiles at launching could do enough damage to cause the catastrophe, officials said.

Any damage to the protective tiles, he wrote, could lead to heating and damage to the underlying structure of the shuttle, particularly near critical spots like the main landing gear door.

A category that is now a focus of the Columbia investigation, the craft's protective tiles, was considered a less likely cause - with a 14.8 percent likelihood - of a catastrophic failure.

Some engineers believe that such forces were to blame for the loss of protective tiles from the tail region of space shuttles when they re-entered the atmosphere.

Doubt About Shuttle Theory Newly recovered data from a recorder on the shuttle Columbia raise doubts that damage to protective tiles led to its destruction.

Several outside experts are questioning whether NASA proceeded too hastily in ruling out the possibility that the foam could have done grave damage to the shuttle's protective tiles.

He described the protective tiles, which shed heat as the orbiter re-enters the atmosphere, as "a very robust system."

But they suspect that the shuttle was beginning to shed, or "slough" pieces of its protective tile.