Guide to Mitigating Spacecraft Charging Effects

Appendix F

Voyager SEMCAP Analysis

As an example of a detailed analysis of a spacecraft and the implications of space charging and resulting ESD events, consider the Voyager story. To simulate the effects of arc discharges on Voyager, tests used a high-voltage-excited spark gap and a flat-plate capacitor with an arc gap to apply arcs on or near the spacecraft. The fields radiated from these sources were approximated in the Specification and Electromagnetic Compatibility Program (SEMCAP) [1], and voltages induced were predicted at key locations using circuit analysis methods. (Note: Details are omitted from this appendix because SEMCAP is no longer supported.) Testing then measured induced voltages at those key locations with an oscilloscope. The data measured were compared to the values predicted to give a measure of accuracy of the computational tools. As can be seen, there are enough unknown variables that the results would be expected to differ from reality.

The mean error between the results measured and those predicted was −12 dB (under predicted), and the standard deviation was 20 dB [2]. Assuming these accuracy parameters to be applicable to predicted in-flight responses for Voyager, the spacecraft was considered to be immune to arc discharges of less than 20 mV on the basis of the SEMCAP analysis. For research applications, a mean offset of 12 dB and standard deviation of 20 dB sound very large. Despite these estimated accuracies, the use of SEMCAP in this application caused ...