HERT

HERT is a compact telescope designed for a 6U CubeSat mission to measure 1-7 MeV electron differential fluxes with a high energy resolution. HERT is built on the heritage of the Relativistic Electron Proton Telescope (REPT)8,9 on the Van Allen Probes10,11, the Relativistic Electron Proton Telescope integrated little experiment (REPTile) instrument on the Colorado Student Space Weather Experiment (CSSWE)12, and the REPTile-2 instrument13 on the Colorado Inner Radiation Belt Experiment (CIRBE)14,15. With simplified electronics and an updated detector design, HERT can provide measurements of 1 – 7 MeV electrons with higher energy resolution (~5% at 1.5 – 3 MeV and <12% otherwise) at a much smaller SWaP (2.2U/3kg/4W) compared to REPT.

HERT consists of three subsystems: sensor head, electrical subsystem, and mechanical subsystem. Its sensor head comprises nine solid-state silicon detectors in a telescope-type configuration. The first detector has a diameter of 20 mm, while the rest have a diameter of 40 mm. Tungsten sheets form a 5 mm stack providing shielding at the front and back of the detector stack, and a 4 mm thick tungsten epoxy chamber comprises the shielding surrounding the detector stack, limiting non- field-of-view (FOV) particles from reaching the detectors. Sheets and tungsten-epoxy instead of solid tungsten are used to ensure that HERT meets the orbital debris requirements. A tantalum collimator with five knife-edged baffles with openings of 18 mm enforces the desired FOV of ~33°. A 1.5 mm thick Beryllium window at the end of the collimator acts as a high-pass filter and prevents low-energy particles (≤ ~0.5 MeV) from depositing sufficient energy (≥ 0.1 MeV) in the detector stack. Figure 1 shows pictures of HERT’s sensor head and the whole assembly.