Combined electron and proton radiation effects on solar cells for earth orbit

Abstract We present a computational approach for accurate calculations of the combined effects of electron and proton radiation in space, tailored to a specific orbit and accounting for the full range of particle energies. The radiation-induced defect formation is shown to depend on the NIEL (Non-Ionizing Energy Loss), which reflects the small fraction of particle energy (from electrons, protons or other ions) lost through the ionisation of the material. The model developed by the Naval Research Laboratory (NRL) for predicting solar cell degradation based on NIEL aligns closely with the results from the Jet Propulsion Laboratory (JPL). However, the JPL model involves a more comprehensive methodology, incorporating experimental validation. To determine the energy dependence of NIEL, S ( E ), for both electrons and protons, we use the ESA NIEL calculation tool. This computational process involves assessing the radiation environment and its effects with an assistance from SPENVIS — a simulation platform developed by ESA/NASA for generating spacecraft trajectories in LEO, MEO or GEO. Proton and electron fluxes are simulated using the International Radiation Environment Near Earth (IRENE) model within SPENVIS. This model offers various calculation options — such as mean, percentile, perturbed or Monte Carlo simulations — based on the mission duration and launch date. The resulting proton and electron fluences, both integral and differential, are used to calculate the Displacement Damage Dose (DDD). This is achieved by integrating the product of NIEL with the differential fluences over the relevant particles energy range. To enhance efficiency, specialized software tools have been developed to extract particle fluxes and fluences from SPENVIS, interpolate them and perform the necessary integration to obtain DDD values for protons, electrons and the combined DDD. Equivalent fluences for defined energy ranges are also provided, enabling detailed, mission-specific radiation analyses. These tools streamline the evaluation of the radiation environment and its impact on solar cells, determining the design and material choices for mission planning and providing the data to predict space power generation throughout the mission’s duration.