Modeling of the Jovian Auroral Environment and Its Effects on Spacecraft Charging

A well-known concern for polar orbiting spacecraft at the Earth is spacecraft charging due to the aurora. Studies of Jupiter reveal the presence of a variety of similar auroral phenomena. In particular, three regions have been identified-a narrow auroral zone at high latitudes, a complex and variable environment over the poles, and auroralike features associated with the main jovian moons and their magnetic flux tubes. These auroral structures are, like their earthly counterparts, expected to be sources of charging. This paper reviews the observational data and models of the jovian aurora zone and polar regions. In combination with models of the jovian plasma environment, the ambient charging currents are then computed with the intention of providing realistic estimates of spacecraft potentials at Jupiter. These are of particular importance to the Juno mission as it is a Jupiter polar orbiter and will pass through the jovian auroral zones near the planet. Of special concern, unlike previous missions to Jupiter, Juno will utilize large solar arrays. While previous missions (e.g., the Voyagers and Galileo) utilized RTGs and were carefully designed to avoid differential surface charging, the Juno mission's solar arrays may make it more sensitive to surface charging. Although the jovian aurora is a possibly serious threat to Juno and similar missions, as will be discussed, an understanding of the environment and proper mitigation techniques should limit their effects.