Trapped Particle Environments of the Outer Planets

Abstract

High-energy, trapped electron and proton environments around the outer planets can pose a serious threat to spacecraft operations. For example, high-energy electrons are a critical source for a phenomenon called internal electrostatic discharge (IESD) which is believed to be the number one cause of spacecraft anomalies in the space radiation environment. Several missions are being considered by NASA that will go to the outer planets (Jupiter, Saturn, Uranus, and Neptune). Indeed, NASA currently has plans to send two spacecraft to Jupiter: one as an orbiter that will perform multiple flybys of Europa and another as a Europa Lander. Of the mission concepts selected for the latest New Frontier Competition, one is to visit Titan, the largest moon of Saturn. Similarly, NASA also has identified missions to Uranus and/or Neptune as potential flagship missions in the last decadal survey. For all of these missions, radiation dose and IESD are potentially critical design parameters. Understanding the trapped election and proton environments at these planets to be able to specify the radiation and IESD design environments for them is an important prerequisite in mitigating these potential hazards. In this paper, we will compare the trapped high-energy electron ( $E > 1$ MeV) and proton ( $E > 5$ –10 MeV) environments at Jupiter, Saturn, Uranus, and Neptune to that at the earth using the latest trapped particle models developed at JPL: GIRE3 for Jupiter, SATRAD for Saturn, UMOD for Uranus, and NMOD for Neptune. The global structure of the electron and proton belts and the dose profiles for possible mission scenarios will be presented and compared.