Trajectory options for RAMSES’ Farinella CubeSat around (99942) Apophis

The 2029 close approach of near-Earth asteroid (99942) Apophis presents an unprecedented opportunity to investigate tidal effects on a rubble-pile body and to advance planetary defense capabilities. In response, the Rapid Apophis Mission for SpacE Safety (RAMSES) has been conceived by the European Space Agency. In order to deliver additional science and complement the scientific objective, RAMSES includes two 6U-XL CubeSats, of which RAMSES CubeSat-1 (RCS-1), named Farinella, is dedicated to the characterization of Apophis’s internal structure and surface properties via a low-frequency radar and high-resolution optical camera from an orbital perspective. This paper investigates the possible trajectory options for RCS-1, allowing the CubeSat to fulfill the scientific objectives, while respecting engineering constraints. To this aim, a high-fidelity dynamical model of Farinella proximity environment, incorporating a polyhedral gravity field, solar radiation pressure, and third-body perturbations from the Sun, Earth, and Moon, is implemented and analyzed. Three classes of candidate trajectories, namely patched hyperbolic arcs, Sun-stabilized terminator orbits, and resonant terminator orbits, are evaluated against scientific return and technical feasibility, considering the spacecraft specifications and instrument requirements that drive orbit design. A detailed trade-off, considering a 21-day timespan preceding the Earth close encounter, is then performed to select the baseline operational orbit, showing that both low-to-medium energy resonant orbits and medium-to–high altitude Sun-synchronous terminator orbits enjoy the best balance among all the considered criteria.