Internal Spacecraft Charging from the Environmental Radiation Monitors on the Van Allen Probes Spacecraft: Charging Driven by Solar Wind Conditions

Spacecraft in orbit within the Earth's radiation belts are subject to hazardous MeV-level particles that can detrimentally impact a variety of subsystems. Furthermore, the degree of spacecraft charging induced within the inner magnetosphere by transient solar-generated interplanetary structures, e.g., coronal mass ejections, co-rotating interaction regions, high speed streams, is fundamentally unknown because of the complex transfer function between the interplanetary medium, magnetosphere, and the actual spacecraft. Yet new space-borne instrumentation and missions require such charging information for proper design considerations. In this study we show how spacecraft charging conditions within Earth's radiation belts change during a variety of transient interplanetary events. The analysis uses data from the Environmental Radiation Monitors aboard the twin Van Allen Probes Spacecraft, and a data set consisting of a wide range of solar wind conditions. We illustrate the relationships between the interplanetary magnetic field strength, solar wind speed and density, and the charging conditions in the inner magnetosphere. The numerous synoptic events are categorized into an initial database that can impact the next generation of radiation models (e.g., AE9 V2.0).