Comparison of spacecraft charging environments at the Earth, Jupiter, and Saturn

Studies of the Earth with the ATS-5, ATS-6, and SCATHA spacecraft led to th e development of several simple tools for predicting the potentials to be e xpected on a spacecraft in the space environment. These tools have been use d to estimate the expected levels of worst case charging at Jupiter and Sat urn for the Galileo and the Cassini spacecraft missions. This paper reviews those results and puts them in the contest of the design issues addressed by each mission including the spacecraft design mitigation strategies adopt ed to limit differential charging. The model shows that shadowed surfaces i n Earth orbit can reach similar to 25 kV or higher in worst case environmen ts, For Galileo, spacecraft-to-space potentials of similar to 900 V were pr edicted in shadow. Since such potentials could produce possible discharges and could effect low energy plasma measurements, the outer surface of Galil eo was designed to rigid conductivity requirements, Even though the surface of Galileo is not entirely conducting, after 27 orbits no adverse effects due to surface charging aside from limited effects on low energy plasma mea surements have been reported. The saturnian environment results in spacecra ft potentials to space in shadow of similar to 100 V or less. Although the overall surface of the Cassini spacecraft was not entirely conducting and g rounded, it is shown that only in the most extreme conditions, is it expect ed that Cassini will experience any effects of surface charging at Saturn.