OVERVIEW

DEFINITIONS

Electromagnetic compatibility (EMC) is the ability of equipment and systems to function in their intended operational environment without adversely affecting or being adversely affected by other equipment, system, or the electromagnetic environment. In order to understand EMC, a basic understanding of Electromagnetic Interference (EMI) is required. The EMI is produced by a source of "culprit" and is detected by a susceptible receptor or "victim". The emissions from the culprit interferes with the normal operation of the victim, and in severe cases, can actually damage the victim. EMI is caused by undesirable radiated electromagnetic fields or conducted voltages and currents. Electronic systems aboard spacecraft can malfunction or become paralyzed if they are not designed to minimize the effects of interference caused by the space electromagnetic environment or by other electrical and electronic components that must operate simultaneously.

Lightning Effects

There are two type of lightning effects experienced when a lightning stroke attaches to the vehicle, facilities, shipping containers/ tranporters, and/or storage containers: 1) Direct effects, or physical damage, usually include high voltage and current-related damage to structures and other hardware. 2) Indirect Effects are malfunctions, either temporary or permanent, experienced by avionics and electrical systems. These effects arise from voltages and currents induced in the avionics equipment and are similar to, but of higher magnitude than, effects from a nearby strike. Direct and indirect effects often occur simultaneously.

Electromagnetic Effects on Spacecraft Systems

There have been spacecraft missions and experiments whose goals and performance were compromised by electromagnetic effects. Problems date back to the Apollo Program. A lightning strike to the launch vehicle during the ascent of the Apollo XII mission resulted in a complete computer memory loss in the Command and Service Module (CSM) due to inadequate lightning protection for the CSM. The Gamma Ray Observatory, launched in 1991, experienced a transponder lockup which prevented communication between the spacecraft and the ground stations. The problem was documented in NASA RP 1374, Electronic Systems Failures and Anomalies Attributed to Electromagnetic Interference.

    
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