Apollo 12 and Atlas-Centaur 67 were the only two U.S. missions ever struck by lightning. In each case, the presence of the launch vehicle in an elevated atmospheric electric field is thought to have triggered the lightning.
Apollo 12 was launched on November 14, 1969, from Kennedy Space Center in Florida. Major electrical disturbances, subsequently attributed to vehicle-triggered lightning, were observed at 36.5 and 52 seconds into the mission. Nine nonessential sensors with solid-state circuits were permanently damaged. Temporary upsets included loss of communication, flashing and sounding of various warning lights and alarms, disconnection of three fuel cells from the power bus, loss of attitude reference by the inertial platform, and disturbances to the timing system, clocks, and other instruments. The mission was able to continue.
At launch, a cold front was passing through the area. Tops of isolated cumulus congestus clouds within a range of 48 kilometers reached a maximum of 7 kilometers. In the vicinity of the launch complex, clouds were reported at altitudes between 240 and 455 meters, with overcast between 600 and 3030 meters. The freezing level was near 3758 meters. No other lightning was reported in the area six hours prior to or after launch.
The vehicle apparently triggered a lightning discharge to ground at 36.5 seconds, when it was at about 1940 meters, and then triggered an intracloud discharge at 52 seconds, when it was at about 4364 meters. In the 20 minutes prior to launch, radioactive electric field probes indicated that the electric field at the launch site was rapidly varying. However, no calibration of the probes was available.
The Atlas-Centaur 67 rocket, carrying the FltSatCom (Fleet Satellite Communications) satellite, was launched on March 26, 1987, from Cape Canaveral. Weather conditions were similar to those at the time of the Apollo 12 launch. A broad cloud mass covered most of Florida and the Gulf of Mexico, and a nearly stationary cold front extended across northern Florida in a southwest-northeast orientation well north of Cape Canaveral.
A squall line, also oriented southwest-northeast, was centered over the eastern Gulf, moving eastward over Florida. It produced substantial amounts of cloud-to-ground lightning activity throughout the day, but most of this activity was well west of the Cape.
At the launch site heavy rain fell, and layered clouds were reported at an altitude between 2424 and 6061 meters. No cloud-to-ground lightning had been observed within 9 kilometers of the launch site in the 42 minutes prior to launch, and only one strike occurred within 18.5 kilometers during this time. At launch, the intensity of the electric field at the field mill site closest to the launch site was -7.8 kilovolts per meter.
At 49 seconds after launch, when the vehicle's altitude was about 3636 meters, a lightning flash was observed. That flash produced at least four strokes to ground as recorded by television cameras. At the time of the strike, the air temperature at the vehicle altitude was 4 degrees Celsius. The freezing altitude was 4242 meters. The vehicle was inside a cloud with a radar echo level of 10 dBZ (radar reflectivity units), far below the value of 40 dBZ generally associated with strong electrification in a thunderstorm.
After the incident, examination of the ground-based electric field mill records indicated that a small cloud discharge probably occurred in the vicinity of the launchpad about two minutes before launch. Members of the press also reported seeing a cloud discharge at about that time.
The lightning strike caused a memory upset in the vehicle guidance system; the upset then caused the vehicle to commence an unplanned yaw rotation. The stresses associated with this motion made the vehicle begin breaking apart. Approximately 40 percent of the telemetry outputs showed anomalous electrical behavior at the time of the event. About 70 seconds after liftoff the Range Safety Officer ordered the vehicle destroyed. Substantial portions of the payload fairing were subsequently recovered from the Atlantic Ocean, and these pieces showed physical evidence of being struck by lightning.