Word: burnthrough
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Dates: during 1980-1989
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...videotape lends support to theories that an O ring was at fault. According to a flight "time-line" compiled by NASA and released at week's end the smoke first appeared .445 seconds after booster ignition. It swirled between the rocket and the external tank, near where the fatal burnthrough seems to have occurred. One solid-rocket specialist noted that because the puff was dark, it probably did not result from combustion of the booster's solid fuel, which produces light-colored smoke. More likely, it came from the burning O ring or the putty placed inside the rings...
...fuel mixture could allow the hot exhaust gases within the booster to reach the rocket's outer steel casing and burn through it. Another possibility was that the flame-retarding material between the booster sections could have loosened under the wide variations in temperature, providing another route for a burnthrough. Most analysts assume that once the flame sliced through the rocket casing, it reached the liquid-fuel tank, burning through either the tank's wall or the connecting fuel lines, touching off the massive explosion...
Indeed, a near burnthrough at a different site on a booster occurred on an earlier Challenger flight, during the summer of 1983. In that case, the insulating material on the interior of the nozzle's throat was scorched away to within half an inch of the nozzle's outer skin...
Still, the way the boosters continued flying after the explosion prompted some experts to reject the likelihood of a burnthrough in either one. Hurled away from the exploding external tank, both rockets appeared to be moving rather stably, producing the awesome Y-shaped pattern that millions of Americans will never forget. A burnthrough on the side of the casing, several rocket specialists say, would have sent the booster cartwheeling wildly through space. Bob Truax, a retired engineer who directed the Thor missile program in the 1950s, agrees. "After the explosion, they were continuing on a fairly normal trajectory," he says...
...week's end the New York Times reported that NASA technicians had found evidence amid the reams of telemetry that seemed to support the burnthrough theory. According to the unnamed source, the data show that the right solid- fuel booster had a pressure drop of nearly 30 lbs. per sq. in. and a loss of 100,000 lbs., or about 4%, of normal thrust about 10 sec. before the explosion --the kind of decrease a burnthrough would have caused. Later the same day, NASA released new pictures and a videotape showing what it called "an unusual plume" of flame streaking...
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