LAUSR

A dynamical model is developed in the body-fixed frame of Phobos, in which the high-precision gravity field and exact physical libration of Phobos, the gravity of Mars with J2, and the gravity perturbations of the Sun, Jupiter, and Earth are considered. The JPL development ephemeris are applied to calculate the positions of celestial bodies. Phobos is considered as a homogeneous polyhedron with 16 037 vertices to characterize its irregular shape and the corresponding gravity field. The physical libration of Phobos is incorporated into its rotational motion by using the results in ‘Report of the IAU WGCCRE’. With the proposed model, equivalent gravity and slope on Phobos surface are calculated and analysed. The liftoff velocity is also computed and presented. Besides, the orbital environment is also investigated. Instantaneous equilibrium points in the Mars–Phobos system are computed and demonstrated, and the acceleration of a particle in the vicinity of Phobos is analysed to find out the main influencing factor in different regions. Quasi-satellite orbits and libration point orbits, which were determined in the circular restricted three-body problem model, are simulated in different dynamical models. The results applying the newly developed high-fidelity dynamical model have shown significant differences with respect to existing models, suggesting that dynamical models with higher accuracy are needed for close-range orbital activities.