Planar spacecraft trajectories in the Didymos–Dimorphos binary asteroid system

The dynamics of a spacecraft in the vicinity of the Didymos and Dimorphos binary system is studied, with specific emphasis on the bounded orbits that exist in such a perturbed gravitational environment. The binary environment is approximated with gradually increasing fidelity, starting with a model that simulates Didymos with an oblate spheroid and Dimorphos with a triaxial ellipsoid. Within these simplifying assumptions, we compute all the families of planar periodic orbits and we study the deviations that arise to them under more realistic perturbations that include the actual shape of Didymos, its rotation, the solar gravity and radiation pressure. To establish the robustness of the different orbital configurations, we perform a classification based on planar dynamical maps and connect the stability regions with the periodic motion. A subset of retrograde orbits around Didymos and a particular type of outer orbits with double multiplicity seem to show long-term stability and robustness, so they can be assumed as safe orbits. On the contrary, orbits around Dimorphos, although stable in the basic model, become strongly unstable in our more realistic model. Our approach is based only on natural dynamics and no active spacecraft control is applied, thus providing a useful methodology in finding ‘safe’ orbits for a spacecraft in the vicinity of a binary asteroid system.