Direct low-energy trajectories to Near-Earth Objects

Near-Earth Objects (NEOs) are asteroids, comets and meteoroids in heliocentric orbits with perihelion below 1.3 au. Similarly to the population of the Main Asteroid Belt, NEOs are primordial bodies, and their study can improve our understanding of the origins of the Solar System. With a catalog of over 30 000 known asteroids and approximately 100 listed short-period comets, the NEO population represents an inventory of exploration targets reachable at a significantly lower cost than the objects of the Main Asteroid Belt. In addition, the materials present in these bodies could be used to resupply spacecraft en route to other destinations. The trajectories of past missions to NEOs have been designed with the patched-conics technique supplemented by impulsive and/or low-thrust maneuvers and planetary gravity assist. The transfer times range from some months to a few years, and the close-approach speeds relative to the target have been as high as 10 km/s. The design technique described in this work leverages the invariant structures of the circular restricted three-body problem (CR3BP) to connect the Earth's vicinity with NEOs in low-eccentricity and low-inclination trajectories in close proximity to the terrestrial orbit. The fundamental building blocks of the method are periodic orbits around the collinear points L₁ and L₂ of the Sun-Earth CR3BP. These orbits are used to generate paths that follow the associated hyperbolic invariant manifolds, exit the sphere of influence of the Earth and reach NEOs on nearby orbits, thus enabling robotic as well as crewed exploration missions to targets in the terrestrial region and asteroid deflection operations. The strategy is simple, can be applied to depart either a libration point orbit or a geocentric orbit, and offers attractive performance features.