Sun-Frozen Orbits Surrounding an Eccentric Binary Asteroid System

The orbital dynamics around binary asteroid systems are primarily perturbed by the nonspherical gravity of binary asteroids and solar radiation pressure. This paper presents semi-analytical models to investigate Sun-frozen orbits surrounding an eccentric binary asteroid system, considering both inner and outer perturbations. A multiple-averaging approach is developed, and a key innovation is the modeling of the apsidal precession caused by the nonspherical gravity of asteroids as a short-period parameter, followed by an additional averaging. This refined model identifies three distinct families of Sun-frozen solutions: terminator, heliotropic, and Sun-line configurations. Then, the existence and stability of Sun-frozen orbits are thoroughly revealed by introducing two dimensionless parameters. Crucially, the obliquity between the binary’s mutual orbit and its heliocentric orbit is demonstrated to consistently degrade orbital stability. A stability correction scheme based on the fast Lyapunov indicator is developed to refine the initial conditions of Sun-frozen orbits in the presence of obliquity. Finally, the derived Sun-frozen orbits are validated by numerical simulations, and the results show superior orbital stability within typical mission lifetimes.