On the design of an Enceladus science orbit

Recent Cassini discoveries of highly active geysers in the southern regions of Enceladus have quickly thrust this small planetary moon into the science spotlight. Unfortunately, the low Enceladus mass and its proximity to Saturn lead to extreme instabilities when considering typical near polar science orbits. Here we find that the usual doubly averaged techniques are invalid for realistic Enceladus orbits. Further, it is shown that a dependence on the low-order averaging assumptions leads to overly-conservative conclusions regarding stability boundaries. Instead, we rely on the results of global searches for periodic orbits in the unaveraged model and demonstrate long-term stable orbits with altitudes near 200 km and inclinations approaching 65°. Prior studies imply the maximum stable inclination is near 45°. The newly discovered orbits provide improved geometry for long-term observations and easy access to brief, near polar excursions for plume experiments.