Technician mounts some of the nearly 8, 000 ceramic-coasted tiles that remain to be installled on the external surface of the Space Shuttle Columbia. A proportion of the 31-34, 000 thermal protection tiles are attached by wires to onboard sensors, which measure characteristics such as temperature & pressure encountered during flight. The tiles, making up the thermal protection system, absorb the intense heat experienced when the spacecraft reenters the Earth's atmosphere.