Design and Instrument Characterization of the High-Energy Resolution relativistic electron Telescope (HERT) using Geant4 Simulation

Abstract

Earth’s outer radiation belt is filled with relativistic and ultrarelativistic electrons in the MeV energy range and above. These highly energetic electrons pose significant threats to avionics and humans in space, and understanding their dynamics has been an urgent need. In the post Van Allen Probes era, measurements of radiation belt populations heavily rely on small space missions such as CubeSats and SmallSats. The Miniaturized High-Energy-Resolution relativistic electron Telescope (HERT) is a compact (≤3U) telescope designed for a CubeSat mission in geosynchronous transfer orbit (GTO). HERT’s main objective is to provide high- energy-resolution measurements of outer belt electrons in an energy range of ∼1 – 7 MeV to help differentiate various mechanisms that accelerate electrons to relativistic and ultrarelativis- tic energies. Geant4 simulations were conducted to characterize the instrument responses. A novel method of using a spherical cap particle source in Geant4 simulation was developed for more efficient instrument characterization. Combined with bow tie analysis, it is demonstrated that HERT will have an energy resolution of 5% for ∼1.5 – 3 MeV electrons and 10% for ∼3-7 MeV. In addition, using the AE9 model, the instrument is shown to have statistically sufficient count rates in the outer belt while not saturating the electronics. With a compact configuration and higher energy resolution in comparison to previous instruments, HERT will significantly contribute to the quantitative understanding of the radiation belt electron dynamics.