One of our priority pieces from Columbia’s underside had arrived at Barksdale—the “sawtooth doubler.” This two-foot by two-foot plate—roughly in the shape of the orbiter itself—had been bonded underneath the orbiter and then covered with tiles. Because the shuttle’s skin was uneven where the doubler was mounted, the tiles covering that part had to be thinner than the surrounding tiles so that the exterior surface of the tiles was smooth. Thinner tiles might not stand up well to the heat of reentry, so it was important to assess the condition of this piece. It was one of the key items in the
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