A chain of errors leading to the launch of Apollo 13

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If NASA hadn’t decided in 1965 it wanted all Apollo electrical systems to be compatible with the 65-volt system used in ground support equipment.

If the contractor building the Apollo Service Module oxygen tanks had informed the subcontractor for the tank’s thermostatic safety switches of the change from 28-volt switches.

If someone had noticed that Apollo’s tanks were still equipped with the lower-capacity switches.

If in 1968 the tanks installed in Apollo 10’s Service Module hadn’t been pulled for modification and swapped out, the old tanks recycled for Apollo 13.

If during the swap out, oxygen tank 2 hadn’t dropped two inches, enough to knock loose a fitting on a drain pipe.

If on March 16, 1970, after the Apollo 13’s Countdown Demonstration Test, oxygen tank 2 had not failed to drain.

If engineers had not decided to boil the oxygen out of the tank by turning on heaters with the 65-volt ground system.

If they’d noticed the thermostatic safety switch inside the tank did not work — were, in fact, fused open by the high current, burning insulation on the wiring inside the tank, leaving exposed wiring waiting to arc in flight once decreasing levels of liquid oxygen exposed them. 

Then one month later, Apollo 13 would have charted a much different course.