| In this study, the feasibility of using libration point orbits to explore small solar system bodies, including asteroids and comets, is considered. A novel design for a small body mission is proposed that makes use of libration point orbits as "parking" orbits. In considering a human exploration mission to asteroids or comets, these "parking" orbits may provide benefits including a safe vantage point for staging/observation, reduced perturbation effects from the nonuniform gravitational field of the body, fewer communication blackouts, ease of guidance and control of a lander on the surface, etc. Because small solar system bodies have extremely low mass ratios in the Sun-small body system, the existence of periodic orbits about the collinear libration points at a safe distance from the smaller primary was uncertain and is demonstrated for a range of small bodies. A two-level differential corrector along with periodicity constraints is proposed for use in computing periodic orbits in the vicinity of the small bodies with significant eccentricity in the Elliptic Restricted Three-Body Problem. Using this method, halo-like orbits are computed in the Sun-433 Eros and Sun-4 Vesta systems. The stability of these orbits is analyzed using Floquet theory. To overcome the effects of perturbations in these unstable orbits, a robust nonlinear station-keeping controller based on sliding mode control theory is proposed. The controller performance is validated in the presence of third-body perturbations from Jupiter, solar radiation pressure perturbations, tracking errors, orbit insertion errors and maneuver burn errors in the Sun-433 Eros and Sun- 4 Vesta systems. Simulation results are presented that show that the small body missions can be designed using libration point orbits with feasible station-keeping costs. |
