Mine is from a brilliant call by NASA flight control Engineer John Aaron that saved the Apollo12 mission after it was struck by lightning during launch.
www.thespaceplace.com/history/apollo/apollo12.html#lightningLift off occurred on schedule on November 14, 1969, at 11:22 a.m. EST. Thirty-six seconds later, as the space vehicle reached 2,000 meters, it was struck by lightning. As Conrad would later recall, "I was aware of a white light. I knew that we were in the clouds; and although I was watching the gauges I was aware of a white light. The next thing I noted was that I heard the master alarm ringing in my ears and I glanced over to the caution and warning panel and it was a sight to behold." Almost every warning light that had anything to do with the electrical system was on. Apollo 12, trailing a plume of ionized (and electrically conductive) exhaust gas, had triggered a lightning discharge. Sixteen seconds later, at an altitude of 4,400 meters, they sustained a second lightning discharge. Conrad told Houston, "We just lost the [stabilizing] platform, gang: I don't know what happened here; we had everything in the world drop out."
At mission control, John Aaron, a bright young flight controller in charge of the electrical system, had no telemetry data on his screen. Aaron had seen this problem before during simulator runs a year before and knew how to fix it. Confidently he said, "Flight, try SCE (Signal Condition Equipment) to Aux." This command was so obscure that neither the flight director, Capcom nor Pete Conrad knew what it meant. It was Alan Bean that knew where to find the switch and moments later, telemetry was back