Today is the 51st anniversary of the launch of Apollo 12, which became famous for it's near abort when the Saturn V was struck by lightening, an action forestalled by the quick thinking of EECOM John Aaron, who issued the call "Try SCE to AUX." https://en.wikipedia.org/wiki/John_Aaron 

This command did not save the mission on its own, but enabled mission control to diagnosis - and then reset - the immense set of system failures that resulted from lightning strike. A critical effect of the strike was to disable the Apollo spacecraft's fuels cells.

The loss of power, pulled the voltages low, disabling the spacecraft's ability to configure its telemetry properly. The controllers got not static, not clear signals, but an odd form of gibberish. A12 also lost their guidance platform. Fortunately the Saturn V had its own.

The whole stack thus continued to fly, but every warning light in the command module was lit up. Hearing Pete Conrad's call listing all the failures is ... spectacular!

But John Aaron, EECOM (lead controller for the spacecraft electrical systems) recognized the gibberish, just as you might recognize the type of foreign language being spoken, even if you could not comprehend it. This was because of his immense curiosity. He had once seen

a test in which the power was accidental pulled low on the CSM (command/service module). He had no duties in the test, he just wanted to watch what they were doing. But he was struck by the garbled telemetry that he saw and asked about it. A tech told him about the SCE,

(signal conditioning equipment box), that packaged all the CSM telemetry for transmission. Seems it had and AUX (auxiliary) setting that would have allowed it to work with low voltage. He filled this away in his head. Curiosity - got to have it! And then right there he saw it!

No one in mission control knew about the SCE. It was never called out in a simulation. But right away without hesitation he called for SCE to AUX. Confused looks from the CAPCOM and Flight - but - they trained as a team and you trusted all your team to do the right thing.

No team of scientists or engineers can work without trust. So the call went up. Commander Conrad didn't know what they were talking about, but Al Bean did - the switch was right in front of him! He set SCE to AUX, and with now good telemetry, Aaron was able to suggest several

commands to bring the fuel cells back on line. The platform would have to wait until they got into orbit, but the mission was saved.

But I have a fun personal connection to this all!

As a space nut I read about this story in 1989 in "Apollo: The Race to the Moon," the best book ever about the ground side of the Apollo program. At the time this event was pretty arcane and had not been celebrated. I went to a book signing by Al Bean in 1998...

Bean was one of the nicest guys you could ever care to meet (and I really wish he was still with us). To me, it was less interesting that he was the fourth one to step out on the moon, than he had ridden as Saturn V that had been struck by lightening 30s after launch. So...

I asked him to sign the book, "SCE to Aux." He looked up visibly startled, and looked me in the eye for a bit, before saying, "You know, in the whole time I've been back from the moon, no one has ever asked me to sign anything like that!" He thought for a while, and then...

wrote a long inscription to follow my request, "Why would anyone want to do a thing like that at a time like this?" And he laughed about the whole thing. A few years latter, he came back to Tucson with Dick Gordan (the CSM pilot of A12) for another book signing, so I asked...

Dick Gordan to sign, too. He quickly said, "Oh yeah, I'll sign what I was thinking then!", which was "It's all up to you, Al!" My daughters, then 4 & 1, were there, and both Dick and Al flirted with them like a couple of indulgent grandfathers. Heroes all - missing them today.