Science orbits in the Saturn-Enceladus circular restricted three-body problem with oblate primaries

This contribution investigates the properties of a category of orbits around Enceladus.The motivation is the interest in the in situ exploration of this moonfollowing Cassini's detection of plumes of water and organic compoundsclose to its south pole. In a previous investigation, a set of heteroclinic connectionswere designed between halo orbits around the equilibrium points L1and L2 of the circular restricted three-body problem with Saturn and Enceladusas primaries. The kinematical and geometrical characteristics of thosetrajectories makes them good candidates as science orbits for the extended observationof the surface of Enceladus: they are highly inclined, they approachthe moon and they are maneuver-free. However, the low heights above thesurface and the strong perturbing effect of Saturn impose a more careful lookat their dynamics, in particular regarding the influence of the polar flatteningof the primaries. Therefore, those solutions are here reconsidered by employinga dynamical model that includes the effect of the oblateness of Saturn andEnceladus, individually and in combination. The dynamical equivalents ofthe halo orbits around the equilibrium points L1 and L2 and their stable and unstable hyperbolic invariant manifolds are obtained in the perturbed models,and maneuver-free heteroclinic connections are identified in the new framework.A systematic comparison with the corresponding solutions of the unperturbedproblem shows that qualitative and quantitative features are not significantlyaltered when the oblateness of the primaries is taken into account. Further-more, it is found that the J2 coefficient of Saturn plays a larger rolethan that of Enceladus. From a mission perspective, the results confirm thescientific value of the solutions obtained in the classical circular restricted threebodyproblem and suggests that this simpler model can be used in a preliminaryfeasibility analysis.