Consistent Modeling of Orbital Perturbations Using Ephemeris Data

A common approach to including the effects of perturbing accelerations on a spacecraft is the “indirect method” with ephemeris data. This method aims to capture the direct gravitational effects of solar system bodies on the spacecraft with an additional (indirect) term that accounts for the mutual gravitation between solar system bodies. An alternate approach, referred to as the “frame center acceleration method,” directly incorporates the complete acceleration of the reference frame center in the dynamics. The focus of this study is comparing the consistency (i.e., the level of agreement between a trajectory propagated in two reference frames and compared in one frame) of trajectories generated using the indirect and frame center acceleration methods when ephemeris data is used to retrieve the positions of the solar system bodies. The results show that the latter method produces more consistent, but potentially less accurate, trajectories than the indirect method across a range of trajectories in the Earth–Moon system. This is due to “unmodeled forces” that are included in the ephemeris but not in the spacecraft force model. The two methods studied here handle these unmodeled forces in different ways. These differences cause the discrepancies in the trajectories generated using the respective methods.