Apollo: The Race To The Moon

by Catherine Bly Cox

In October 1968, when the O2 Tank 2 used in Apollo 13 was at North American, it was dropped. It was only a two-inch drop, and no one could detect any damage, but it seems likely that the jolt loosened the fill tube that put liquid oxygen into the tank. In March 1970, three weeks before the flight, Apollo 13 underwent its Countdown Demonstration Test that, like all C.D.D.T.s, involved loading all the cryos. When the test was over, O2 Tank 2 was still 92 percent full, and it wouldn’t detank normally—probably because of the loose fill tube. Because a problem in the fill tube would have no effect on the tank’s operation during flight, the malfunction was not thought to be relevant to flight safety. After three unsuccessful attempts to empty the tank, it was decided to boil off the oxygen by using the internal heater and fan. This was considered to be the best procedure because it reproduced the way the system would work during flight: heating the liquid oxygen, raising its pressure, converting it to gas, and expelling it through the valves and pipes into the fuel cells where, in flight, it would react with the hydrogen. So they turned on the tank’s heater. A technician working the night shift on Pad 39A was assigned to keep an eye on the tank temperature gauge and make sure that it did not go over 85 degrees Fahrenheit. It was not really necessary that a human serve this function, because a safety switch inside the tank would cut off the heaters if the temperature went beyond ...