Modeling of Electric Fields Inside Spacecraft Dielectrics Using In-Orbit Charging Current Data

Internal charging caused by energetic electrons is a threat to critical space infrastructure such as Europe's Galileo navigation satellites, however, the mechanism involved and its relationship to space weather is still poorly understood. While the electric field developed inside on-board dielectrics is accepted to be of prime importance, it has never been measured in orbit. On the other hand, internal charging currents have now been measured in a GPS-like medium Earth orbit (MEO) over a ten-year period, so we have used these data to model the electric fields of concern. The measured charging currents provide both charge deposition and dose rate inputs to the electric field model, the latter allowing the introduction of radiation-induced conductivity (RIC) to improve realism. As expected we find that RIC is a mitigating factor for the electric fields but they can still become very large, e.g., a 1.0-mm thickness of PEEK under 0.5 mm of Al shielding would be at risk of breakdown almost throughout the mission. We find that RIC tends to reduce sensitivity to space weather perturbations of the environment such as the April 2010 storm event, and hence longer term average fluxes seem to be more important. This seems physically reasonable for the examples studied but we also know that some satellite anomalies do show a correlation with space weather storms and short term (daily) electron fluences and so further work is needed to understand such cases: for example model parameters could be adjusted to see under what circumstances short term variations are more influential. To enable the progressive improvement of such modeling in future we recommend wider deployment of charging current sensors, especially in MEO and geostationary orbits.