Perspectives on the Distributions of ESD Breakdowns for Spacecraft Charging Applications
Electrostatic discharge (ESD) continues to pose significant risks to space missions despite decades of intense study. We emphasize here the advantages to spacecraft designers and modelers from considering the stochastic distributions of breakdown and how it can be affected by factors including spacecraft environment conditions, design geometries, material temperature, material purity, charging history, and appropriate timescales. Spacecraft charging models and spacecraft designs typically rely on tabulated values or ranges of breakdown strength, often based on cursory measurements with little or no experimental detail. Depending on the timescales and history of environmental and orbital changes or durations of specific missions, it may be critical to consider breakdown as a probability distribution rather than a single number or range of values.
We present measured distributions of ESD data across several test configurations and materials including low density polyethylene (LDPE), polyimide (Kapton HN or PI) and biaxially oriented polypropylene (BOPP). Step-up ramp-to-breakdown tests measured the distribution of breakdowns as a function of applied field at various fixed ramp rates and temperatures. Time endurance tests measured breakdown after some time for samples held at sub-critical static electrostatic fields. Taken together, these tests begin to provide an understanding of the probability of breakdown, what tests are most applicable, and how to interpret this for specific missions and charging concerns.
Achieving statistically significant results as described above for several candidate materials can be onerous, even with accelerated test methods. We have observed pre-arcing events (transient, non-shorting, current spikes) during voltage ramp-up tests with sufficiently slow ramp rates. The distributions of these events have a strong correlation with the distributions of ESD events in many polymeric materials. We propose that experiments observing pre-arcing versus applied electric field could be used a proxy for step-up to breakdown ESD tests to significantly accelerate sample characterization.
*This work was supported by a NASA Space Technology Research Fellowship and funding through NASA GSFC and the James Webb Space Telescope.