Aerospaceweb.org | Ask Us - Apollo 12 Lightning Strike

Apollo 12 Lightning Strike

- question from H. F. Wadsworth

The flight you are probably referring to is Apollo 12, the second mission to land on the Moon. The mission was launched from the Kennedy Space Center in Florida on 14 November 1969. Aboard the command module, named Yankee Clipper, was command module pilot Dick Gordon in the center seat, mission commander Pete Conrad to his left, and lunar module pilot Alan Bean seated to his right. While all systems were go for launch, launch controllers were somewhat concerned about the weather. Storm clouds had gathered in the vicinity even before the astronauts had been sealed into the capsule, by which point the crew reported drops of water on the Yankee Clipper's windows. After careful review of the weather, however, the controllers concluded that the conditions were within safety tolerances and the countdown proceeded.

Liftoff of Apollo 12

The Saturn V rocket intended to send the three men on their journey to the Moon lifted off at 11:22 AM local time. All appeared normal until 36 seconds later when, at an altitude of about 6,500 ft (2,000 m), Pete Conrad saw a bright flash of light and the capsule's master alarm began wailing in distress. As Conrad later recalled, "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."

Apollo 12 ascending into overcast skies

The command module's instrument panel was lit up with countless warnings, nearly all related to the craft's electrical system. What no one had yet realized was that Apollo 12 had just been struck by lightning. As the rocket accelerated through the low-altitude rain clouds, it behaved much like a lightning rod. A bolt of electricity struck the vehicle and traveled to the ground along the column of ionized, electrically conductive gases in the rocket engine exhaust plume of the Saturn V.

A bolt of lightning that struck Apollo 12 during liftoff

The lightning strike primarily affected the fuel cells located in the service module. These critical devices generated power for the command module but were momentarily disabled by a power surge due to the lightning. Even though power was automatically switched to a battery backup system, the lightning had also cut off telemetry contact with Mission Control in Houston so that engineers on the ground had no data on what was going on inside the spacecraft.

Apollo Command and Service Modules and Launch Escape System (click for larger image)

The situation worsened even further when a second bolt of lightning struck the rocket 52 seconds into the mission at an altitude of about 14,500 ft (4,400 m). This strike jolted the navigation system within the command module causing Conrad to report to 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, engineers struggled to understand what had happened to the vehicle. Neither flight director Gerry Griffin nor senior controllers had ever experienced such a situation and contemplated ordering an abort. In that case, the crew would use the launch escape rockets mounted atop the command module to jettison their capsule from the rest of the Saturn V and make an emergency landing off the Florida coast. Once the crew were clear of the rocket, the mighty Saturn V would have been destroyed by ground controllers using self-destruct explosives, and Apollo 12 would have come to a premature conclusion.

Gerry Griffin then turned to a 24 year old engineer named John Aaron, who oversaw the electrical system on the mission, and asked, "What do you see?" Though his display had turned from valid flight telemetry to a meaningless jumble of numbers, Aaron had a sudden inspiration. He had seen a similar problem occur during training simulations a year earlier and remembered how it had been fixed.

Over the communication system, Aaron gave the command, "Flight, try SCE [Signal Condition Equipment] to Aux." Neither Pete Conrad aboard Apollo 12, flight director Griffin, nor the capsule communicator (CapCom) had any idea what this obscure command referred to. Luckily, Alan Bean remembered that the SCE switch was located near his seat and followed Aaron's instructions. The flight telemetry was restored in Mission Control moments later, and the ground engineers saw that the vehicle was still operating properly.

Although the electrical and navigation systems within the command module had been affected by the lightning strike, the guidance system on the Saturn V had continued to function perfectly. This system kept the rocket on its proper path into Earth orbit, and the mission was never in any danger. The crew managed to get the fuel cells back up again shortly after the second stage engine ignited, and the command module's inertial guidance system was realigned once in orbit. Apollo 12 entered its planned Earth parking orbit 11 minutes and 44 seconds after liftoff. Once all systems had been checked out and no damage was discovered, Mission Control reported, "Apollo 12, the good word is you're Go for TLI [Translunar Injection]." With that approval, the third stage was ignited, and the crew continued on to the Moon.

What the crew was not told, however, was of the ground controllers' concern that the lightning may have damaged the pyrotechnic system used to deploy the command module's parachutes prior to splashdown. Had they failed, the capsule would have struck the ocean at a speed of 300 mph (480 km/h) killing the crew instantly. Luckily, no other problems were encountered during Apollo 12, and the crew returned safely following their successful lunar landing. All this thanks to the quick thinking of young flight controller John Aaron and timely actions of astronaut Alan Bean.
- answer by Jeff Scott, 7 September 2003

Aircraft | Design | Ask Us | Shop | Search