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 ×10
⁶
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.