Exploration of Asteroids and Comets with Innovative Propulsion Systems

In recent decades, growing interest has arisen within the scientific community in asteroids, in particular near-Earth objects (NEOs), which are asteroids or comets characterized by a semimajor axis close to that of the Earth. Interest in these objects is motivated not only by their capability of providing answers to important questions concerning the origins of the solar system, but also by the threat of a possible future collision with Earth. It is quite common for NEOs to have peculiar orbits, with non-negligible inclinations and/or eccentricities. This implies that a rendezvous mission with such objects requires a large propellant consumption and gravity-assist maneuvers that significantly increase flight time when chemical (and also electrical) thrusters are used. Therefore, a promising option for exploring NEOs is provided by a propellantless propulsive system as solar sails or electric solar wind sails (E-sails), which are capable of generating thrust without consuming any propellant. In this chapter, the optimal solar sail- or E-sail-based transfers towards some of themost relevant NEOs are generated by solving an optimal control problem through an indirect approach. The results are compared with the transfer times obtained assuming a chemical thruster and a bi-impulsive maneuver.