Thermal tiles key to shuttle's survival

Monday, February 3, 2003 Posted: 5:22 PM EST (2222 GMT) - original reference

(CNN) -- So long as they work, the white and black tiles that cover NASA's space shuttles hardly merit a second glance.

The tiles, some no larger than adhesive floor coverings available at home-improvement stores, are crucial to a spacecraft's survival. They form the thin skin that separates the shuttle and its crew from temperatures that exceed 2,000 degrees Fahrenheit as the craft hurtles back into the Earth's atmosphere.

Heat-deflecting devices have been central components on all of NASA's craft since the agency began suborbital flights around the Earth more than four decades ago. Scientists have performed unceasing research, striving to improve their thermal qualities.

The Columbia was covered with 22,000 tiles and thermal-protection blankets -- some designed to handle the extremely high temperatures of atmospheric re-entry, others engineered to respond to the demands of orbital flight. They had served that shuttle and others well, said Ron Dittemore, NASA's top shuttle program manager.

"Our tile has performed wonderfully," he said at a news conference Sunday afternoon in Houston, Texas.

According to NASA, about 70 percent of a shuttle's exterior is shielded by tiles made of a silica fiber compound, a material derived from common sand. The fibers are mixed with deionized water and other chemicals and poured into a plastic mold, where excess liquid is squeezed out. They are then baked in the nation's largest microwave, in Sunnyvale, California, and fused in a 2,350 degree oven.

The tiles vary according to their location on a shuttle and the demands placed on them:

High-temperature reusable surface insulation tiles are used on the upper forward fuselage and most of the underside and other areas that can be exposed to temperatures reaching 2,300 degrees as the craft returns to Earth. They are black

A newer type of black tile, called fibrous refractory composite insulation, has replaced some of the older black tiles on selected areas of shuttles.

Low-temperature reusable surface insulation tiles are used on parts of the forward, middle and aft fuselage. They also appear on parts of the vertical tail and upper wing, and are designed to protect the craft where temperatures are below 1,200 degrees. They are white to provide better thermal protection in orbit.

Advanced flexible reusable surface insulation has replaced much of the white tile. It is a blanket made of insulation batting between two sewn-together layers of white fabric. Tests showed that the blanket thermal protection was more durable and lighter than the white tiles.