Setback for Apollo
By contrast, the U.S. space program was not faring so well. After almost two months of intensive investigation into the oxygen-tank explosion during the aborted Apollo 13 moon flight, NASA's high-level review board confirmed that the accident was probably caused by an arcing short that ignited Teflon insulation on wiring in the tank. The fire in turn damaged the seal at the top of the tank and generated heat that expanded the oxygen. The resulting pressure caused the weakened area to burst. The board also detailed an extraordinary sequence of bungling uncovered by the $1,000,000 postmortem.
As far back as 1965, the 1,113-page report said, Apollo's prime contractor, North American Rockwell, had ordered that specifications for two small electric switches used to cut off the oxygen tank's internal heater be increased to 65 volts. Inexplicably, the subcontractor for the tanks, Beech Aircraft, kept delivering switches with a top rating of only 28 volts. Despite elaborate checkout procedures that were repeated through six previous Apollo manned missions, neither NASA nor its suppliers ever detected the oversight. Indeed, the error might never have been discovered if it had not been seriously compounded by other blunders just before the launch of Apollo 13.
Unable to empty out the tank during tests at the Cape, NASA technicians applied 65 volts to the heater, trying to boil off the semiliquid oxygen. The voltage fused the inadequate 28-volt cutoff switches, allowing the temperature in the tank to rise to 1000DEG F. and damaging the Teflon insulation on the wires. This led to the arcing that occurred during the mission. Why did the Cape Kennedy technicians have to resort to this untried procedure for emptying the tank? Because, said the panel, the tiny tube through which oxygen is fed in and extracted had probably been shaken loose when the tank was dropped two inches at the North American plant in Downey, Calif.
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