Analysis of air termination system of the lightning protection scheme for the Indian satellite launch pad

Any satellite launch mission is a complex and expensive process and great care and precautions need to be taken for a safe and successful launch. A lightning stroke can be hazardous to the satellite launch system. Therefore extensive care has to be taken to protect the satellite launch pad against lightning. The paper aims at evaluating the efficacy of the aerial receptor system of the lightning protection scheme employed for protecting the Indian satellite launch pad. Significant upward leader activities are expected from tall objects during the approach of the descending leader and therefore any method that is employed for evaluating their attractive radii must take into account the different process involving and connected with the breakdown of air. Among such models the Rizk model, originally developed for isolated towers and conductors, was found to be very appropriate for the present work. To apply it to the present problem many modifications were necessary; all the simulations were carried out using this modified model. The charge simulation method has been used for the computation of the electric field. Simulations with inclined downward leaders indicated that the vertical leader descent represents the worst case scenario, and hence all the calculations were carried out with a vertical leader descent only. The maximum current in a bypass stroke was found to be 14 kA and this occurs for a stroke descending vertically along a straight line directly above the launch vehicle. The total probability of bypass strokes was found to be in the range of one flash per 1095-510 years (for the value of Td which is reported to be between 50-90 thunderstorm-days per year). Similarly, the total number strokes to the protection system in an year was estimated to be less than two flashes per year. Further, some sensitivity analysis was also carried out to determine the dependency of bypass stroke on height of the protection system and total length of the descending leader. An attempt was also made to arrive at a rough estimate of maximum bypass current under positive lightning.