This paper describes the initial operations and preliminary results of the
Instrument for the study of Stable/Storm-time Space (ISSS) onboard the microsatellite
Next Generation Small Satellite-1 (NEXTSat-1), which was launched on December 4, 2018
into a sun-synchronous orbit at an altitude of 575 km with an orbital inclination angle
of 97.7°. The spacecraft and the instruments have been working normally, and the results
from the observations are in agreement with those from other satellites. Nevertheless,
improvement in both the spacecraft/instrument operation and the analysis is suggested to
produce more fruitful scientific results from the satellite operations. It is expected
that the ISSS observations will become the main mission of the NEXTSat-1 at the end of
2020, when the technological experiments and astronomical observations terminate after
two years of operation.
Monitoring the Earth's radiation belt by Low-Earth-Orbit (LEO) satellites has a long history and complemented observations near the high-altitude equatorial plane. However, most of the previous LEO missions suffered from limitations in energy resolution, energy range, L-shell coverage, or the mission lifetime, which leave room for further improvement in this topic. Here we present multi-year (January 2019~February 2021) observations of energetic (0.03 MeV~1.8 MeV) electrons by the Korean NextSat-1 (altitude~575 km) with high energy resolution (0.006-0.4 MeV) and seamless L-shell coverage. For <80 keV electrons, the slot-region outer edge moves inward with increasing geomagnetic activity, which agrees with previous Van Allen Probes reports. The behavior is more conspicuous for lower-energy electrons. Latitudinal profiles of outer-belt electron flux are smoother equatorward of the geosynchronous footprint latitudes (|MLAT|~66 o ) than poleward. The NextSat-1 electron flux is positively correlated to geosynchronous observations, with the coefficient generally higher for higher electron energies. Also, both the geosynchronous and NextSat-1 data exhibit similar spectral indices close to -3 in the log-log space. All these results complement and expand previous knowledge on energetic electrons. The main findings are discussed in the context of existing literature.
In this paper, we present observations of the Space Radiation Detectors (SRDs)
onboard the Next Generation Small Satellite-1 (NEXTSat-1) satellite. The SRDs, which are
a part of the Instruments for the study of Stable/Storm-time Space (ISSS), consist of
the Medium-Energy Particle Detector (MEPD) and the High-Energy Particle Detector (HEPD).
The MEPD can detect electrons, ions, and neutrals with energies ranging from 20 to 400
keV, and the HEPD can detect electrons over an energy range from 0.35 to 2 MeV. In this
paper, we report an event where particle flux enhancements due to substorm injections
are clearly identified in the MEPD A observations at energies of tens of keV.
Additionally, we report a specific example observation of the electron distributions
over a wide energy range in which we identify electron spatial distributions with
energies of tens to hundreds of keV from the MEPD and with energy ranging up to a few
MeV from the HEPD in the slot region and outer radiation belts. In addition, for an
~1.5-year period, we confirm that the HEPD successfully observed the well-known outer
radiation belt electron flux distributions and their variations in time and L shell in a
way consistent with the geomagnetic disturbance levels. Last, we find that the inner
edge of the outer radiation belt is mostly coincident with the plasmapause locations in
L, somewhat more consistent at subrelativistic energies than at relativistic energies.
Based on these example events, we conclude that the SRD observations are of reliable
quality, so they are useful for understanding the dynamics of the inner magnetosphere,
including substorms and radiation belt variations.
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