Change as an Accident Cause
Friday last was the 45th anniversary of the splashdown of Odyssey, the Apollo 13 command module, after it survived a nearly disastrous explosion on the outbound journey to the moon.
The enroute spaceship consisted of command, service, and lunar modules.
Odyssey was equipped with two spherical liquid oxygen tanks for breathing air, water and the production of electricity.
About 55 hours into the flight during a routine stirring procedure, tank two exploded causing a cascade of events culminating in the powering down of the command module and the crew moving into Aquarius, the lunar module, as the details of a rescue attempt were worked out.
The rescue and return to earth is well documented in Apollo 13, the movie and in Lost Moon, Commander Jim Lovell’s book.
The cause is less well understood.
It began with a simple oversight.
Damaged Service Module
The oxygen tank had both a heater and a thermostat powered by Odyssey’s 28 volt DC system.
At some point the system was upgraded to 65 volt ground-based power but the heater and thermostat were not.
During a pre-launch test the thermostat and heater were powered up.
The thermostat contacts failed in the open position and it went unnoticed despite that fact that a chart recorder accurately showed that the heater was not cycling on and off to keep the sphere at 80F.
Internal tank temperature reached 1,000F and the teflon and wiring baked to a crisp setting the stage for the explosion.
And there was this: the temperature gauge had a maximum reading of 80F so the critical temperature was never visible.
Ditching Aquarius
Goodbye Aquarius
Having provided a lifesaving shelter for the return to earth, Aquarius had to be gotten rid of though the normal procedure was unusable because of damage to Odyssey.
A team of six University of Toronto engineers was given one day to figure out a solution and they did.
With no control rocketry available the engineers devised a plan to pressurize the tunnel connecting Odyssey to Aquarius.
The added pressure would force the two apart.
It worked and the three-man crew splashed down alive and well, all things considered.
Splashdown
Sources: NYT, Wiki, Lost Moon, a Man on the Moon