I asked pops what he knew about the challenger boom-boom, this is what he replied:
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The ambient temperature was near 40 deg causing the massive amount of steel and the rubber 0-rings 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 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 neoprene or 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 was probably close to 75% of designed.
My company made the ablative insulating rings that covered the flanges of the solid booster segments.
The solid booster was made in sections, approximately 12' long by 18' in diameter. Solid propellant was cast and cured inside the steel cylinders and then machined to the final ballistic configuration.
These segments were shipped by rail from Thiokol in Utah to the Cape where they were stacked with o-rings between the flanges.
After assembly of the motor segments, the "Kick Rings" were used to cover the flanges.
The kick rings were ablative insulators designed to prevent the extreme heat from burning through the steel motor cases.
The "kick rings" were fabricated by laying up silica-phenolic fabric patterns and then curing in an autoclave.
The cured rings were then machined to the final configuration.
Each ring was made up of several segments that were assembled into the final ring when installed on the booster motor.
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