Apollo and America's Moon Landing Program: Analysis of Apollo 12 Lightning Incident - Technical Report on the Triggered Lightning Strike on the Apollo Saturn V Rocket in 1969

This official NASA technical report - converted for accurate flowing-text e-book format reproduction - provides an analysis of the famous 1969 triggered lightning strike on the Apollo 12 rocket during its launch.

The summary states:

The Apollo 12 space vehicle was launched on November 14, 1969. at 11:22 a.m. e.s.t. from launch complex 39A at Kennedy Space Center, Florida. At 36.5 seconds and again at 52 seconds, a major electrical disturbance was caused by lightning. As a result, many temporary effects were noted in both the launch vehicle and spacecraft. Some permanent effects were noted in the spacecraft and involved the loss of nine non-essential instrumentation sensors. All noted effects were associated with solid-state circuits, which are the most susceptible to the effects of a discharge.

Analysis shows that lightning can be triggered by the presence of the long electrical length created by the space vehicle and its exhaust plume in an electric field which would not otherwise have produced natural lightning. Electric fields with sufficient charge for triggered lightning can be expected to contain weather conditions such as the clouds associated with the cold front through which the Apollo 12 vehicle was launched. The possibility that the Apollo vehicle might trigger lightning had not been considered previously.

The Apollo space vehicle design is such that a small risk of triggered lightning is acceptable. In accepting this minimal risk for future flights, launch rule restrictions have been imposed with respect to operations in weather conditions associated with potentially hazardous electric fields.

Before the Apollo 12 flight, the only consideration of the effects of lightning on the space vehicle was for the period prior to flight. The methods and procedures used to cope with possible lightning prior to launch have been in existence since the inception of the launch complex. The possibility of the vehicle becoming involved with lightning after lift-off was not a launch consideration, unless natural lightning activity was actually present in the launch complex area.