Expanding Gravitational Capture Sets via planetary moon flybys in Sun–planet systems

The gravitational capture technique in the three-body system plays a crucial role in low-energy planetary capture by leveraging the gravitational interactions among celestial bodies to alter the spacecraft's energy. The core of this technique is the Gravitational Capture Set (GCS), which represents the complete set of initial conditions associated with gravitational capture trajectories. However, the GCS is severely constrained by the spacecraft's energy upon entering the planetary system. In particular, when the entry energy is exceptionally high, GC opportunities become exceedingly rare. To address this challenge, this paper proposes a method for expanding the GCS via planetary moon flybys (PMFs). This approach exploits PMFs to reduce the spacecraft's entry energy. Consequently, it greatly increases GC opportunities and effectively expands the GCS without additional maneuvers. Taking the Sun–Jupiter system as an example, this method presents a novel GCS generated by a flyby of Callisto. The results demonstrate that a close flyby of Callisto effectively lowers the spacecraft's energy. This enables numerous objects, initially on escape trajectories with respect to Jupiter, to be gravitationally captured. As a result, this approach not only significantly extends Jupiter's GCS but also reveals several novel types of ballistic capture motions.