Low-energy and low-thrust exploration tour of Saturnian moons with full lunar surface coverage

This study presents the trajectory design for a mission touring the Inner Large Moons of Saturn—Rhea, Dione, Tethys, Enceladus, and Mimas—engineered to satisfy observational requirements, including full surface coverage, as defined by the scientific community and major space agencies, while ensuring low fuel consumption and compatibility with current power and propulsion technologies (radioisotope thermoelectric generators and Hall effect thrusters). The tour begins at Rhea and concludes at Mimas, employing a trajectory concept that alternates between extended observation phases around each moon and Saturn-centered low-thrust spiral arcs to transition efficiently to the next target in the sequence. The J2[jls-end-space/]-perturbed Circular Restricted Three-Body Problem is the dynamical model adopted for the design of exploration paths around the moons, with halo orbits used as staging points for heteroclinic and homoclinic loops that guarantee prolonged, repeated, and comprehensive surface reconnaissance of the targets (including critical regions such as Enceladus’ poles, where geological activity manifests through intense material plumes). Stable and unstable hyperbolic invariant manifolds of the halo orbits act as departure and arrival gateways for propelled inter-moon transfers. The latter are modeled in an ephemeris-based framework with the inclusion of the relevant gravitational perturbations induced by the moons of the system, the Sun, and the oblateness of Saturn. The dynamical model setup is carried out through a rigorous perturbation analysis to maximize computational efficiency while ensuring a high-fidelity trajectory design. A locally-optimal guidance law is used to minimize propellant consumption. The proposed tour represents an alternative to traditional flyby-based missions, offering comparable total duration yet with a greater fraction of observing time and reduced fuel requirements. It advances previous work by achieving both complete lunar surface coverage and high-fidelity trajectory modeling.