Medium Energy Electron Telescope (MEET)

We propose to develop a miniaturized electron telescope, the Medium Energy Electron Tele-scope (MEET), to fit into a 1U (10x10x10 cm3) of a CubeSat to measure 30-400 keV electrons in the inner radiation belt (L<3) in a highly inclined low Earth orbit (LEO). Such an orbit has the unique advantage of separating electron measurements from trapped energetic protons based on location since trapped energetic protons are relatively stable and are seen by LEO spacecraft only in the South Atlantic Anomaly (SAA). In contrast, the Van Allen Probes, in low inclination geo-transfer orbits, have shown again that instruments in the inner radiation belt are subject to penetrat-ing energetic protons (10s of MeV to GeV). The Relativistic Electron Proton Telescope (REPT) and the Magnetic Electron and Ion Spectrometer (MagEIS) on the Van Allen Probes are heavily shielded but still experience proton contamination and despite sophisticated procedures to remove this background uncertainties remain. The inner belt electrons have recently been shown to be more interesting than previously be-lieved. For instance, measurements from the Relativistic Electron Proton Telescope integrated little experiment (REPTile, a simplified and miniaturized version of REPT) on board the Colorado Stu-dent Space Weather Experiment (CSSWE), a 3U CubeSat in a highly inclined (65o) LEO revealed that galactic cosmic-ray albedo neutron decay (CRAND) is a significant source of energetic elec-trons in the inner belt. (In CRAND, cosmic rays interact with the upper atmosphere to produce al-bedo neutrons which β-decay to produce energetic electrons.) This discovery was made possible by a highly inclined LEO where all three populations of electrons could be measured. REPTile was able to measure stably-trapped, quasi-trapped (electrons that are lost before completing a complete drift around the Earth), and precipitating electrons thanks to the asymmetry of the Earth's magnetic field. However, REPTile had only three energy channels: 0.50 – 1.63, 1.63-3.8 and >3.8 MeV. Even more interesting is the dynamic behavior of lower energy electrons (<300 keV) in the in-ner belt. They respond to storms and substorms implying the penetration of convection electric fields deep into the inner magnetosphere that is not well understood. Electron measurements by DEMETER, another satellite in a highly inclined LEO, revealed an excessive number of <300 keV electrons in the inner belt that cannot be explained by CRAND. A recent study has shown that measurements of <200 keV electrons by DEMETER in the inner belt were severely saturated dur-ing active times showing that accurate measurements of 30-400 keV electrons in the inner belt are still lacking. These advancements beg for a deeper understanding of these energetic electrons in the inner belt: their source, loss, intensity, and cause of their dynamic variation. We propose to develop MEET to address these issues. Methodology. MEET differs from our previous REPTile in that it will measure lower energy (30-400keV) electrons and by incorporating pulse height analysis (PHA) will have much finer energy resolution (>40 energy channels instead of three) and by applying anti-coincidence to veto events from side and back penetrating protons will make cleaner measurements. There are two main tech-nical challenges: (1) avoiding saturation from the higher electron fluxes at lower energies and (2) measuring the smaller energy depositions of these lower electrons in the detector. To overcome (1), we will use a smaller geometric factor (a smaller detector area and a longer collimator to restrict the field of view) and a front foil to block <30 keV electrons. As for (2), we propose to use a thinner and smaller silicon detector to increase the detector's response time and reduce the detector's noise. Detailed GEANT4 simulations will be conducted throughout the design, building, and testing phases to guide our designs and validate the results.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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