Cable Bundle Response in SGEMP Analysis

Assessment of the vulnerability of electronic systems to SGEMP requires the knowledge of currents and voltages appearing at individual interface circuits. Recent assessment practices treat coupling either as an interaction of the fields with each individual wire isolated from the remaining wires in the bundle, or as an interaction with all the wires in the bundle as a single entity. We describe here an effort to predict the coupling of the bulk current to individual wire current using both a detailed and simplified model of the cable bundle. The loads were chosen to represent a typical distribution of loads on a spacecraft, and the ability of the models to predict the coupling was investigated. Measurements of the coupling were made on two-cable bundles in the laboratory, and the results are compared to those predicted by the models. Calculations of the probability of survival of typical interface circuits show that the 10 dB accuracy to which the currents can be predicted with the simplified models requires only a modest increase in safety margin over the safety margin required with exact knowledge of the currents.