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

Earth\u27s 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 \u3c 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\u27s 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 \u3c ~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\u27s 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\u27s 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

Two Generations of CubeSat Missions (CSSWE and CIRBE) to Take on the Challenges of Measuring Relativistic Electrons in the Earth’s Magnetosphere

The Colorado Student Space Weather Experiment (CSSWE) CubeSat, carrying the Relativistic Electron and Proton Telescope integrated little experiment (REPTile) to measure 0.5 to \u3e3.8 MeV electrons and 8-40 MeV protons, operated for over two years, 2012-2014, in low Earth orbit (LEO). There have been 25 peer-reviewed publications, including two in Nature, and five Ph.D. dissertations associated with CSSWE. Another 3U CubeSat mission: Colorado Inner Radiation Belt Electron Experiment (CIRBE), has been under development to address an unresolved science question: Where is the break point in terms of electron energy below which electrons can be transported into the inner belt from the outer belt but above which they cannot? This requires clean measurements of energetic electrons with fine energy resolution in an environment where all instruments are subject to the unforgiving penetration from highly energetic protons (tens of MeV to GeV). An advanced version of REPTile has been designed and built, REPTile-2. It has been integrated into the CIRBE bus, which has active attitude control, deployable solar panels, and a S-band radio, provided by Blue Canyon Technologies. CIRBE advances our science capabilities and has significantly improved performance vs. CSSWE and is ready to be launched into a LEO in early 2023