Abstract: The Jet Propulsion Laboratory, California Institute of Technology, in the early 1980s developed a comprehensive model of the jovian electron and proton radiation environments (E>100 keV) under the direction of Dr. Neil Divine. That model was based primarily on in-situ measurements from the Pioneer 10, Pioneer 11, and Voyager spacecraft. Recently the high energy electron component of that model ... between ~8 and ~16 Rj has been updated using data from the Galileo spacecraft (i.e., the Galileo Interim Radiation Electron Model or "GIRE"). The updated software package, along with a report describing the GIRE model upgrade, the steps leading to its creation, and relevant issues and concerns, has been prepared and is available through Open Channel. Included with the report are complete FORTRAN source code listings of the programs used to analyze the EPD data and to generate the GIRE model. The GIRE model, along with original Divine model components required to run it, the necessary data files, and sample input and output data are provided as a stand-alone software package. The GIRE software package provides the trapped radiation belt intensity spectra inside ~16 Rj for the electrons (based on the original Divine mode as updated between 8-16 Rj) and inside ~12 Rj for the protons (based on the original Divine model formulation).

Measurements of the high-energy, omni-directional electron environment by the Galileo spacecraft Energetic Particle Detector (EPD) were used to develop a new model of Jupiter's trapped electron radiation in the jovian equatorial plane for the range 8 to 16 Jupiter radii (1 jovian radius = 71,400 km). 10-minute averages of these data formed an extensive database of observations of the jovian radiation belts between Jupiter orbit insertion (JOI) in 1995 and 2002. These data were then averaged to provide a differential flux spectrum at 0.174, 0.304, 0.527, 1.5, 2.0, 11.0, and 31 MeV in the jovian equatorial plane as a function of radial distance. This omni-directional, equatorial model was combined with components of the original Divine model of jovian electron radiation to yield estimates of the out-of-plane radiation environment. That model, referred to here as the Galileo Interim Radiation Electron (or GIRE) model, was then used to calculate the Europa mission dose for an average and a 1-sigma worst-case situation. The prediction of the GIRE model is about a factor of 2 lower than the Divine model estimate over the range of 100 to 1000 mils (2.54 to 25.4 mm) of aluminum shielding, but exceeds the Divine model by about 50% for thicker shielding. While work remains to be done, the GIRE model clearly represents a significant step forward in the study of the jovian radiation environment, and it is a useful and valuable tool for estimating that environment for future space missions.