  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
with 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 vicinity of the
Earth with NEOs in low-eccentricity, low-inclination orbits. The fundamental
building blocks are periodic orbits around the collinear points L$_1$ and L$_2$
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. The strategy is simple, can be applied
to depart either a libration point orbit or the vicinity of the Earth, and
offers attractive performance features.
