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 the development of several simple tools for predicting the potentials to be expected on a spacecraft in the space environment. These tools have been used to estimate the expected levels of worst case charging at Jupiter and Saturn for the Galileo and the Cassini missions. This paper reviews those results and puts them in the context of the design issues addressed by each mission. In the case of Galileo, spacecraft to space potentials of ~1000 V were predicted. As such levels could produce possible discharges and could effect low energy plasma measurements, the outer surface of Galileo was held to rigid conductivity requirements. Even though the surface of Galileo was not entirely conducting, after 14 orbits no adverse effects due to surface charging have been reported. The Saturnian environment, in contrast to Jupiter, results in spacecraft potentials to space of ~100 V--levels. The overall surface of the Cassini spacecraft also was not entirely conducting and grounded. Here it is shown that only in the most extreme conditions is it expected that Cassini will experience any effects of surface charging at Saturn. Those conditions are presented and the likely consequences are mentioned.