The transient observation-based particle (TOP) model and its potential application in radiation effects evaluation

The evaluation of the radiation hazards on components used in space environment is based on the knowledge of the radiation level encountered on orbit. The models that are widely used to assess the near-Earth environment for a given mission are empirical trapped radiation models derived from a compilation of spacecraft measurements. However, these models are static and hence are not suited for describing the short timescale variations of geomagnetic conditions. The transient observation-based particle (TOP)-model tends to break with this classical approach by introducing dynamic features based on the observation and characterization of transient particle flux events in addition to classical mapping of steady-state flux levels. In order to get a preliminary version of an operational model (actually only available for electrons at low Earth orbit, LEO), (i) the steady-state flux level, (ii) the flux enhancements probability distribution functions, and (iii) the flux decay-time constants (at given energy and positions in space) were determined, and an original dynamic model skeleton with these input parameters has been developed. The methodology is fully described and first flux predictions from the model are presented. In order to evaluate the net effects of radiation on a component, it is important to have an efficient tool that calculates the transfer of the outer radiation environment through the spacecraft material, toward the location of the component under investigation. Using the TOP-model space radiation fluxes and the transmitted radiation environment characteristics derived through GEANT4 calculations, a case study for electron flux/dose variations in a small silicon volume is performed. Potential cases are assessed where the dynamic of the spacecraft radiation environment may have an impact on the observed radiation effects.