Great read. Thanks for posting Wolf.
Speaking of engineering, the link above "The Devil's in the Details” has some interesting details…
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…the wiring inside the [O2] tanks be rated to function at 28 volts, this is the voltage the tanks would be operated at in space. Beech in turn subcontracted for the thermostatic safety switches used inside the cryogenic tanks, specifying a 28-volt operating environment.
Three years later, NASA decided that it wanted the electrical systems of the Apollo spacecraft to be completely compatible with the 65 volts used in the ground-support and test equipment at Cape Canaveral in Florida, in addition to the lower levels used in space. North American informed Beech Aircraft of the change, but Beech never informed its subcontractor, so the thermostatic safety switches were never upgraded to operate above 28 volts. [UHHH Ohhh]
Still, the Apollo 13 service module probably could have gotten away with using the underrated switches, if not for an accident that occurred in 1968. Along with its twin, oxygen tank one, oxygen tank two was installed in the service module that would fly as part of the Apollo 10 mission. Because of an unrelated problem, oxygen tanks one and two in Apollo 10 were swapped out for another pair, and the originals went into Apollo13. But during the swap, oxygen tank two was dropped about 5 centimeters.
The tank was inspected and appeared to be fine, and so it was installed in Apollo 13's service module. During a test about a month before Apollo 13's launch in 1970, the tank was filled with liquid oxygen. All went well until gas was pumped into the tank to empty it by forcing the liquid oxygen out under pressure. Oxygen tank two failed to empty. (The official investigation into the Apollo 13 crisis later surmised that the 5- centimeter drop in 1968 had knocked a fitting loose inside the tank, preventing normal emptying.)
Stuck with a tank full of liquid oxygen, the test engineers eventually decided to turn on the heaters built into the tank to boil off the oxygen. The heaters were connected to the 65-volt ground-power supply, which fused the thermostatic switches shut. Instead of tripping open when temperatures in the tank reached 27 degrees C, the switches allowed the heaters to keep running as temperatures inside the tank soared to more than 500 degrees C. [UHHH Ohhh] This high temperature damaged the Teflon insulation coating the wires near the heaters and left exposed wiring within the tank. Later, when the spacecraft was already on its way to the moon, it was this wiring that sparked when the tank fans were turned on, which in turn led to the Teflon insulation igniting. The resulting fire sent pressures within the tank through the roof, and the tank blew up.
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I read somewhere else that Lovell, as commander of the flight, was aware of the previous problem with the O2 tank, and had signed off the gripe prior to launch of Apollo 13.
