Low-Energy and Low-Thrust Exploration Tour of Saturnian Moons with Full Lunar Surface Coverage

Abstract

This study presents the trajectory design for a mission touring Saturn's Inner Large Moons (Rhea, Dione, Tethys, Enceladus, and Mimas) engineered to meet observational requirements, including full surface coverage, 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 ends at Mimas, using 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. The J2-perturbed Circular Restricted Three-Body Problem is adopted to design exploration paths, with halo orbits serving as staging points for heteroclinic and homoclinic loops that enable prolonged, repeated, and comprehensive surface reconnaissance (including critical regions such as Enceladus poles, where geological activity produces intense plumes). Stable and unstable hyperbolic invariant manifolds of the halo orbits act as departure and arrival gateways for propelled inter-moon transfers, modeled in an ephemeris-based framework including gravitational perturbations from the moons, the Sun, and Saturn's oblateness. The dynamical model setup is guided by a rigorous perturbation analysis to maximize computational efficiency while maintaining high fidelity trajectory design. A locally optimal guidance law minimizes propellant consumption. The proposed tour offers an alternative to traditional flyby missions, providing comparable total duration but greater observing time and reduced fuel requirements, and advances previous work by achieving both complete lunar surface coverage and high-fidelity modeling.

Figures (15)

• Figure 1: Sketch of the MT strategy, highlighting the dynamical models used in the distinct phases of the tour.
• Figure 2: Reference frames used in the dynamical model.
• Figure 3: Scheme of a system consisting of two oblate, homogeneous spheroids with axes of maximum inertia parallel to each other.
• Figure 4: Configuration of the CR3BP showing the primaries ${m}_1$ and ${m}_2$, the spacecraft $S/C$, and the Lagrange equilibrium points in the synodic barycentric reference frame.
• Figure 5: Families of halo orbits around $L_1$ and $L_2$ in the $J_2$-perturbed Saturn–Enceladus CR3BP (Enceladus-centered synodic reference frame). The families are characterized by $C_J \in [3.00252, 3.00257]$, with a $C_J$ spacing of $2.0\times10^{-6}$ between consecutive orbits.