Apollo 12 Lightning Strike: The First Three Minutes and Why "SCE to Aux" Worked

Apollo 12 was hit by lightning twice on November 14, 1969: 36.5 seconds after liftoff and again at 52 seconds. The Saturn V rocket kept flying on its own guidance, but the Command Module lost all three fuel cells, its guidance platform tumbled, and the data reaching Mission Control turned to nonsense. A three-word call, "SCE to Aux," brought the data back, and the crew had the fuel cells on line again about 2 minutes and 22 seconds into the flight.

Watch the 47-second version on Orbital Focus's Instagram or TikTok. This page is the long version: the transcript second by second, what the switch actually did, which popular details are wrong, and a small checklist built from how John Aaron prepared for a problem nobody had simulated.

What happened

Apollo 12 lifted off from Launch Complex 39A at 11:22 a.m. EST, into low rain clouds. NASA's post-flight analysis concluded that the rocket and its long exhaust plume triggered the lightning itself, something no one had considered before the flight. The first discharge came at about 6,400 feet, the second at about 14,400 feet.

Three things went wrong at once in the spacecraft:

• Power. All three fuel cells disconnected from the power buses. The Command Module's two entry batteries carried the 75-amp load alone, and the bus voltage sagged to about 24 volts.
• Guidance. The second strike made the spacecraft's inertial platform lose its reference and start to tumble.
• Data. The lightning knocked out the primary power supply of the Signal Conditioning Equipment (SCE), so the numbers streaming to Houston no longer made sense.

The Saturn V's own instrument unit, which was steering the rocket, was essentially unaffected. That detail matters later.

Minute-by-minute timeline

Times are ground elapsed time from liftoff, as printed in the Apollo Flight Journal. "Onboard" lines came from the cockpit recorder and were not heard in Houston at the time. The last column is our annotation.

The mission went on to the Moon. Five days after launch, Conrad and Bean landed Intrepid about 535 feet from Surveyor 3, a robotic lander that had been sitting there since April 1967, and brought pieces of it home.

What SCE to Aux did

The Signal Conditioning Equipment took readings from sensors around the spacecraft and converted them to a standard 0 to 5 volt range, so other electronics could turn them into numbers for recording and transmission to Earth. When the lightning knocked out the SCE's primary power supply, the numbers Houston saw were garbage. Mission Control could not tell which systems had actually failed.

The SCE power switch sat at the bottom of Panel 3, in front of Lunar Module Pilot Alan Bean, with three positions: OFF, NORMAL and AUX. Moving it to AUX ran the unit from its auxiliary supply. It did not fix the fuel cells. It fixed the view of them, which let the ground tell the crew exactly what to reset.

Gerry Griffin, the flight director, put it bluntly in his 1999 oral history: "I'd never heard of the switch. We'd never touched it. Never used it, out of all those hundreds of switches."

Why Aaron knew

John Aaron was the EECOM, the flight controller responsible for the spacecraft's electrical and environmental systems. In his 2000 oral history, he explained that in Houston's simulators a power failure like this made the readings drop to zero. On Apollo 12 they did not.

He had seen the real signature once before. "I happened to be on the third shift one night watching a test of the command module that they were performing at Kennedy," he said. The test crew dropped all power on the vehicle to go on battery, and the numbers "didn't go to zero. They were at 6.7, 12.3. I mean, some squirrelly kind of numbers."

He did not let it go. "I drove home that night, thinking where did those squirrelly numbers come from. And the next morning I came in the office and I sat down with Dick Brown," a North American engineer in his office. "We sat down and went through all the circuitry to find out just how does this thing work."

His own summary is modest: "The way luck played into that was, again, luck and curiosity." And: "So it wasn't that I understood exactly what had happened, I recognized a pattern and how to get out of it."

Myths and corrections

Retellings of this story drift. These are the details most often wrong, checked against the primary sources.

One quote carries a caveat: Aaron's exact words "Flight, EECOM. Try SCE to AUX." come from the Apollo Flight Journal's transcription of the flight director loop audio. The official 1969 transcript covers only air-to-ground, where the words the crew heard were Carr's: "Try SCE to Auxiliary."

After the flight, NASA amended its launch rules so that no launch would be attempted in weather where lightning was likely to form.

The pattern card

Aaron did not solve a problem he had studied for. He had noticed an odd reading once, refused to leave it unexplained, and traced it through the circuitry the next morning with a colleague. That habit translates to debugging code, fixing a machine, or studying a subject where the practice problems do not look like the real test.

This is an editorial routine drawn from his account, not a tested study method.

A blank card to copy:

Griffin's side of the story adds one more habit: before touching anything, he checked what was still working. "I remember looking down at those five engines, and they were all still right on the money pressure wise," he said, and the rocket was "gaining altitude right up the flight dynamics officer's preplanned plot." When something breaks, confirm what has not broken before you change anything.

If the odd result shows up mid-task, park it in a list with the brain dump method instead of chasing it right away. When a missing piece of understanding stalls a study session, the studying recovery guide covers how to tell a knowledge gap from a distraction. For step 3, a 10-minute timer is enough to start the trace. In Orbital Focus you can name the mission's payload after the question, such as "Why didn't the readings go to zero?", so the session has one job. The payload guide explains how that works.

Frequently asked questions

What does SCE to Aux mean?

SCE is the Signal Conditioning Equipment, the unit that converted readings from the spacecraft's sensors into a standard 0 to 5 volt form before they were digitized for recording and transmission to Earth. Aux switched it to its auxiliary power supply. After the lightning knocked out its primary supply, that switch brought readable data back to Mission Control.

Did lightning almost make Apollo 12 abort?

Flight director Gerry Griffin later said he thought they were going to have to abort. He also decided not to abort early while the Saturn V was still climbing on its planned path, and Pete Conrad said in the 1969 debrief that he never considered an abort. Under the launch rules, losing telemetry alone was not grounds for an abort.

Who flipped the SCE switch on Apollo 12?

Lunar Module Pilot Alan Bean. The switch sat at the bottom of Panel 3, in front of his seat. Griffin's oral history and the Apollo Flight Journal both credit Bean; the popular version in which Dick Gordon told him to do it does not appear in the transcript.

Sources

All sources checked September 24, 2026.

• Apollo 12 Flight Journal, Day 1 Part 1: Launch to Earth Orbit. Air-to-ground and onboard transcript with commentary; source of every timestamped quote, the SCE description, the 75-amp and 28-volt figures, the 2:22 fuel cell reconnection and Conrad's debrief quote.
• More than SCE to AUX: Apollo 12 Lightning Strike Incident, Johannes Kemppanen, Apollo Flight Journal, updated February 15, 2025. Flight director loop transcription, Panel 3 location, abort-rule context and the amended launch rules.
• Analysis of Apollo 12 Lightning Incident, NASA, February 1970. Launch time, strike times and altitudes, triggered lightning and the SCE dropout.
• John W. Aaron oral history, NASA Johnson Space Center Oral History Project, January 18, 2000, pages 12-16 and 12-17.
• Gerald D. Griffin oral history, NASA Johnson Space Center Oral History Project, March 12, 1999, pages 12-9 to 12-15.
• Apollo 12: The Pinpoint Mission, NASA. Telemetry loss at 36 and 52 seconds, the 535-foot landing distance and Surveyor 3's April 20, 1967 landing.

Images: the hero frame is from NASA 16 mm launch-pad film (public domain), scanned by Ed Hengeveld for Project Apollo Archive, via Wikimedia Commons. The photo of John Aaron is NASA S69-59590 (public domain), via NASA on The Commons. Send corrections to habib225@gmail.com.

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