TID and Internal Charging Evaluation for Jupiter Orbiting Mission

Abstract

In the Jovian radiation belt, the radiations of high-energy particles are much higher than that in the earth’s radiation belt. The radiation hardness is a key technology to ensure the successful implementation of the Jupiter mission. We develop the methods of total ionizing dose (TID) and internal charging evaluation for a potential Jupiter orbiting mission. In TID evaluation, based on the data from radiation test on devices, the Jovian radiation belt model, and the solar proton model, we introduce a method to evaluate the failure possibility caused by TID after shielding layers. In this method, radiation variability in Jovian magnetosphere and failure dose uncertainty of devices are integrated. Survival probability can be studied quantitatively. Especially we define the failure rate and investigate its change within the mission period. Using this method, we can approach a balance among device ability, shielding thickness, and failure probability in the spacecraft design. In internal charging evaluation, the simulation method is improved and applied to the Jovian mission. A worst case electron environment with 99% percentile is chosen. Shielding properties of high- $Z$ and low- $Z$ materials are studied. As a result, tantalum is twice better than aluminum in shielding efficiency and benefits in two aspects: lower range and higher backscatter parameter of the energetic electron. The analysis algorithms of depth-dose curves up to 100-MeV electrons are studied. Then, the charging $E$ -fields of dielectrics in time-varying flux are investigated. For Fr4 with high conductivity, peak $E$ -field is determined by periapsis flux. For Kapton with low conductivity, the deposited electrons can accumulate between different orbits and the $E$ -field increases gradually. In both TID and internal charging evaluation, we also compare the differences of results in Jupiter orbit with that in geosynchronous of Earth.