Just for giggles, I sent an e-mail to pops asking what he knew about it, I seem to recall he submitted a white paper soon after the explosion and that he worked in conjunction with Morton thikol on many rocket motor projects over the years.
He explained that the coefficient of thermal explansion delta between the materials caused the compression on the ring to decrease, and the colder temperature prevented it from expanding enough to maintain enough pressure to hold back the fuel.
Here's part of it:
Quote:
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The ambient temperature was near 40 deg causing the massive amount of steel and the rubber 0-ring to thermally shrink causing the o-ring compression to be below that required to hold the motor pressure. It was rumored that political influence was brought to bare to go on with the firing even through the Thiokol engineers I spoke to vehemently opposed it. The coefficient of thermal expansion of steel is about 6 X 10 to the minus 6 inches/inch/deg F and that of the rubber O-ring material (probably Buta-diene) is about 12 X 10 to the minus 5 inches/inch/deg F. Normal design temperature is usually about 75 deg F and the temp at firing was 35 deg below that. The resultant thermally caused reduction in O-ring compression to probably close to 75% of designed.
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