Field Mapping Techniques for Lightning Protection

The lightning mast and overhead ground wire are well-established methods for protecting structures from direct lightning strokes. The advent of space vehicles and missiles with stored or contained propellants, and the exposure of extremely sensitive circuitry, compel the design engineer to investigate the degree of lightning hazard and to inquire into the margin of safety provided by these conventional methods of protection. Field mapping techniques and field equation analysis are powerful tools for such investigations. This paper presents a condensed discussion of basic lightning phenomena, field mapping methods for determining the pre-strike field conditions, and a field equation analysis of the transition from the static to the dynamic state. This analysis is provided for the pre-strike period, the lightning stroke and follow-through period, and is continued until static field conditions are restored.