## 6 Discussion and Conclusions  
The NASA AE9/AP9/SPM set of models represents an important approach to specify the radiation environment for modern satellite design applications. In this work, this suite of models has been employed to estimate trapped proton fluxes over the South Atlantic Anomaly for some orbits of the China Seismo-Electromagnetic Satellite on 1 January 2021. This is intended as a starting point for a future analysis that will include data from the High-Energy Particle Detector. After three years of calibration and testing, HEPD has proven capable of measuring low-energy particle fluxes (\(>\)3 MeV electrons and \(>\)35 MeV protons) with precision and stability over time; among the others, these two characteristics in particular are very suitable for the measurement of strongly anisotropic particle fluxes, such as those trapped in SAA. Thus, HEPD, together with the other payloads on board CSES (such as those of the HEPP suite), can provide excellent cross-calibration for these radiation environment models at LEO. A preliminary analysis on HEPD proton data has been conducted to assess the agreement between the AP9 model and experimental data, and it seems already acceptable, even if some discrepancies--that need to be studied--are present. It is important to remember, as already mentioned, that there is also a certain number of known issues in these models:  
* There are no reliable data for inner region electrons at energies \(<\)1 MeV and spectral/spatial extrapolation of the few existing datasets can lead to large deviations. * There are no data for high-energy protons (\(>\)150 MeV). AP9 goes out to 400 MeV only by using physics-based model extrapolation techniques. Moreover, much of the validation of these models was performed using the Van Allen Probe mission [46], which provided a rich set of energetic particle and plasma data from the many instruments the spacecraft carried on board, together with a good pitch angle and energy resolution; unfortunately, after the end of the mission, new data are necessary  
Figure 6: Time profiles (5-s resolution) of 50 MeV trapped protons estimated from the Ap9 model and compared with preliminary data of \(\sim\)50 MeV proton data (black circles) from the HEPD instrument on board the CSES-01 satellite. The analysis has been carried out using the procedure described in [40]. The agreement between the data and the model appears generally good, despite showing small discrepancies, especially in the peripheral regions of the SAA. Only statistical errors are reported. to continue validation and to explore higher energy ranges with more statistics. HEPD proved to be able to cover this role, performing measurements with precision and stability in time; besides, new CSES missions (with more HEPD-like particle detectors) are already planned for the next years, greatly expanding the data-taking period by several years into the 2020s. Writing original draft, M.M. ([PERSON]); Conceptualization, R.S; Writing-review and editing, R.S., R.B., L.C. ([PERSON]), F.M.F., M.P. ([PERSON]), A.P., C.D.D., A.S., F.P. ([PERSON]); Designing the experiment or calibration or data production and processing, S.B., R.B., W.J.B., D.C., L.C. ([PERSON]), G.C., L.C. ([PERSON]), A.C., C.D.D., C.D.S., F.M.F., R.I., I.L., N.M., G.M., M.M. ([PERSON]), A.O., G.O., F.P. ([PERSON]), F.P. ([PERSON]), B.P., A.P., F.P. ([PERSON]), P.P., M.P. ([PERSON]), M.P. ([PERSON]), E.R., M.R., S.B.R., Z.S., V.S., A.S., V.V., S.Z., P.Z. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The following abbreviations are used in this manuscript:  
CSSES China Seismo-Electromagnetic Satellite  
HEPD High-Energy Particle Detector  
SAA South Atlantic Anomaly  
AFRL Air Force Research Laboratory  
TLE Two-Line Elements  
SGP4 Simplified General Perturbations  
CRAND Cosmic Ray Albedo Neutron Decay  
SEE Single Event Effect  
NRO National Reconnaissance Office  
VDL Virtual Distributed Laboratory  
LEO Low-Earth Orbit  
ELSET Element Set