This proposal covering the five years period of february 1ST. 2018 to january 31ST. 2023 presents the numerical enhancement and computational implementation of spatial and time dependent trapped…

This is a five-year cooperative agreement awarded by the National Aeronautics and Space Administration (NASA) Shared Services Center to the Old Dominion University Research Foundation (Odurf), a non-profit organization, to enhance and computationally implement spatial and time-dependent trapped proton/electron radiation environment models within the Earth's geomagnetic field. The models will also account for the effects of galactic cosmic rays (GCR) on spacecraft. The work will focus on improving particle absorption and scattering algorithms as input to radiation transport codes, and coupling the models to atmospheric attenuation and ionization models. The $1,247,995.85 contract will be used to update the existing AP8/AE8 trapped particle models with the latest International Geophysical Reference Field (IGRF) data and provide improved radiation environment predictions for low Earth orbit (LEO), medium Earth orbit (MEO), and geosynchronous orbit (GEO) through 2025. The results will be used for space ionizing radiation analysis studies.

This proposal covering the five years period of february 1ST. 2018 to january 31ST. 2023 presents the numerical enhancement and computational implementation of spatial and time dependent trapped proton/electron radiation environment models within the earth geomagnetic field. The models will also account for the effects of incoming particle fields of galactic cosmic rays (GCR), both at the surface and within the interior of a spacecraft. IT proposes the implementation of the most recent magnetic field model definition to be coupled with time dependent models of the radiation environments to be found at low earth orbit (LEO) in the range of 400~2000 kilometers (KM), medium earth orbit (MEO) in the range of 2000~25000 KM and geostationary orbit (GSO) at 35793 KM. The models are to be used in the space ionizing radiation analysis studies. The work will deal with the improvement of the particle absorption and scattering algorithms needed as input to the radiation transport codes (deterministic or stochastic), accounting for the presence of ions, electrons, photons, pions/muons and neutrons. The models can be coupled to available atmospheric attenuation ionization model, to account for the effects of atmospheric attenuation on the incoming particle fields of both GCR and solar origin at the LEO, MEO and GSO altitudes. Consideration will also be given to the study of radiation survivability of communications and weather satellites in geosynchronous (GEO, altitude: 35,793 KM) and GSO due to high flux of trapped electrons. Currently, the most widely used trapped particle radiation environment definition near earth is based on the NASA s static AP8/AE8 models which define the trapped proton and electron intensities. These models are based on a large number of satellite measurements carried out in the 1960S and 1970S. In this proposal, the AP8/AE8 models as well as a heavy ions GCR model will be updated with the most recent international geophysical radiation field (igrf) reference database to define the radiation environments for protons, electrons and heavy ions at LEO, MEO and GEO (or GSO). Updated LEO and MEO dosimetric calculations will be included in the analysis since any launch platform capable of delivering a payload to GEO will accumulate exposure during its transit through LEO and MEO. This will provide prediction capability to define the radiation environment with high degree of accuracy up to 2020 during the first three years of this effort, followed by an update to 2025 during the last two years of this proposal. The particle transport approach taken in this proposal will be to use the LEO, MEO, GEO trapped and geomagnetically attenuated GCR environments as input to the langley research center (larc) developed deterministic particle transport codes high charge (z) and energy transport (hzetrn), coupled electron photon transport (ceptrn) and meson transport (mestrn) which are now combined in a comprehensive transport code called HZETRN2015. This will be done through exposure prediction within simple geometries such as spherical shell, or a large modular structure represented by a specific configuration of the international space station (ISS). Based on the results of the simulations, conclusions will be drawn on the exposure levels accumulated by these geometries throughout a mission to at LEO, MEO and GEO.