Radiation Noise Effects at Jupiter’s Moon Europa: In-Situ and Laboratory Measurements and Radiation Transport Calculations

There is great scientific interest of Jupiter´s moon Europa and in performing further spacecraft investigations. However, successful measurements at this satellite are difficult because transient charge pulses produced by Jupiter´s magnetospheric radiation can significantly degrade signals. In order to develop shielding and mitigation approaches for future Europa missions, we investigated the radiation noise produced in the Galileo spacecraft´s Near Infrared Mapping Spectrometer (NIMS) in the jovian magnetosphere. We then analyzed the radiation-transport characteristics of the NIMS shield and calculated the shielding efficiencies for thicker shields. Major findings are (1) NIMS data obtained at the orbital radius of Europa yield a rate of transient charge pulses (“hits”) of 1.5 ×10⁶ cm^-2 s^-1 behind 5 mm of Ta shielding, (2) radiation transport calculations indicate a decrease in the hit rate with increased shielding, achieving a factor of 10 reduction for 30 mm thick walls, (3) γ-ray photons produced in the shield (and possibly the surrounding instrument and the spacecraft itself) are equally or more important in generating radiation noise, and (4) γ-rays, with their mean-free-paths greater than the range of electrons with the same energy, are difficult to shield so heavier shielding is less beneficial than previously predicted.