Design, Characterization, and Testing of HERT, a Miniaturized High-Energy-Resolution Relativistic Electron Telescope for CubeSats

Design, Characterization, and Testing of HERT, a Miniaturized High-Energy-Resolution Relativistic Electron Telescope for CubeSats

Utah State University, Logan, UT

Earth's outer radiation belt is filled with relativistic 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. As CubeSats increasingly play a more prominent role by executing missions at a far lower cost, they become ideal vehicles for conducting such scientific investigations. The miniaturized High-Energy-Resolution relativistic electron Telescope (HERT) is a compact telescope designed for a 6U CubeSat mission in a geosynchronous transfer orbit (GTO). HERT aims to provide high-energy-resolution (dE/E < 12%) measurements of 1 - 7 MeV electrons at GTO. These measurements will enable a novel method to differentiate the two main acceleration mechanisms, inward radial transport and local acceleration, and solve the longstanding question of how electrons in the Earth's radiation belts are accelerated to relativistic energies. Building upon the heritage of the Relativistic Electron Proton Telescope (REPT) instrument on the Van Allen Probes and the REPTile-2 instrument on CIRBE, HERT iS comprised of a stack of nine solid-state silicon detectors in a telescope configuration with a beryllium window to block lower energy electrons and a tantalum collimator to enforce the required FOV (33°). The instrument responses were investigated using Geant4 simulations, and the results project HERT to have a nominal energy resolution of ~5% for 1.5 - 3 Me V electrons and < ~12% for other core energy channels. Radiation testing has been conducted with a Cobalt-60 source, and the results suggest that HERT electronics can sustain a total ionizing dose of ~65 krad, meeting the instrument performance requirement in a GTO. Random vibration simulations have also been conducted, which suggest that HERT's reaction stresses and displacements are within a significant safety factor relative to yield strength from each component. Bench testing with muons and an SR-90/Y-90 radioactive source is ongoing to test HERT's performance. With a high energy resolution and a miniaturized design, HERT will greatly advance the quantitative understanding of relativistic electron acceleration in the outer radiation belt.