Empirical models of the low‐energy plasma in the inner magnetosphere

Abstract

Particle flux measurements by the Charge and Mass Magnetospheric Ion Composition Experiment/Magnetospheric Ion Composition Spectrometer (CAMMICE/MICS) and Hydra instruments on the NASA Polar satellite have been used to build empirical models of the plasma environment at low energies in the Earth's inner magnetosphere. These models may be used to develop design and to test specifications for spacecraft surface materials, which are susceptible to damage by the ions. The combination of the CAMMICE/MICS and Hydra models provides the ion flux at energies in the range 20 eV to 200 keV as a function of position in the magnetosphere. For the 1–200 keV energy range, the H+ and O+ ion flux is estimated separately using the CAMMICE/MICS data. Average environments have been calculated for several sample orbital trajectories: a geosynchronous orbit and the orbits of several satellites in the Global Positioning System (GPS) constellation. At high energies (∼100 keV), the flux estimates agree with corresponding estimates from the NASA AP‐8 model, but the fluxes at low energies are larger than those extrapolated simply from AP‐8. The CAMMICE/MICS model shows that H+ dominates the >2 keV ion populations, but the O+ flux becomes comparable to the H+ flux at ∼1 keV. The standard deviation of both the ion and electron flux was found to be 100–200% of the average value over the entire considered energy range. The average 1–200 keV O+ flux estimates for GEO appear similar to the averages for GPS orbit, so material damage due to O+ in this energy range should be similar for the two orbits.