HEPD on NEXTSat-1: A High Energy Particle Detector for Measurements of Precipitating Radiation Belt Electrons

Radiation belt particles of the inner magnetosphere precipitate into the atmosphere in the subauroral regions when they are pitch-anglescattered into the loss cone by wave-particle interactions. Such particle precipitations are known to be especially enhanced during space storms, though they can also occur during quiet times. The observed characteristics of precipitating electrons can be distinctively different, in their time series as well as in their spectra, depending on the waves involved. The present paper describes the High Energy Particle Detector(HEPD) on board the Next Generation Small Satellite-1 (NEXTSat-1), which will measure these radiation belt electrons from a low- Earth polar orbitsatellite to study the mechanisms related to electron precipitationin the sub-auroral regions. The HEPD is based on silicon barrier detectors and consists of three telescopes that are mounted on the satellite to have angles of 0 ◦, 45 ◦, and 90 ◦, respectively with the local geomagnetic field during observations. With a high time resolution of 32 Hz and a high spectral resolution of 11 channels over the energy range from ~ 350 keV to ~ 2 MeV, together with the pitch angleinformation provided by the three telescopes, HEPD is capable of identifying physical processes, such as microburstsand dust-side relativistic electron precipitation(DREP) events associated with electron precipitations. NextSat-1 is scheduled for launch in early 2018.