Real Time Internal Charging Model for Geostationary Orbit

Internal charging is a recognized threat to spacecraft operating in the energetic electron environments present in geostationary orbit. Spacecraft designers typically evaluate charging threats based on conservative design environments when deciding what materials can be used or shielding that must be included to mitigate the charging threat. Once satellites are on orbit, operators can monitor the energetic electron flux and fluence or use a number of threat prediction tools to determine if threat environments are present. We describe an alternative approach using a real-time model that takes the next step beyond monitoring electron flux: computation of the dynamic electric fields present in insulating materials generated by the charge densities produced by penetrating energetic electrons. Input data for the code is obtained from the GOES satellites in geostationary orbit or can be derived from radiation belt models. The charging code is the 1-D NUMIT (for "numerical iteration") charging model that computes charge density and electric field as a function of depth in insulating materials. Model output is electric field as a function of depth in the insulator, material conductivity, and radiation shielding to reduce the incident electron flux. Satellite operators will benefit from access to a predictive model for estimating electric fields in materials that approximate their own applications. The model will be run in real time at NASA's Community Coordinated Modeling Center.