Consistent Modeling of Orbital Perturbations Using Ephemeris Data

Overview

This research examines two methodological approaches for modeling orbital perturbations using ephemeris data: the indirect method and the frame center acceleration method. The indirect method incorporates direct gravitational effects of solar system bodies on the spacecraft alongside an additional term accounting for mutual gravitation between solar system bodies. The frame center acceleration method directly incorporates the complete acceleration of the reference frame center in the dynamics equations. The study evaluates the consistency of trajectories generated by each method when applied to spacecraft dynamics in the Earth-Moon system.

Methods and approach

The investigation employs comparative analysis of trajectory propagation across two reference frames, with consistency defined as the level of agreement between trajectories propagated in different frames and subsequently compared in a single frame. Ephemeris data is utilized to retrieve positions of solar system bodies for both methods. The analysis encompasses a range of trajectories within the Earth-Moon system to assess performance across different orbital regimes and configurations.

Key Findings

The frame center acceleration method produces trajectories demonstrating greater consistency than those generated by the indirect method across the tested range of Earth-Moon system trajectories. However, this enhanced consistency is accompanied by potentially reduced accuracy in absolute trajectory predictions. The differential handling of unmodeled forces present in ephemeris data but absent from the spacecraft force model accounts for discrepancies between the two methods. These unmodeled forces represent gravitational and other perturbative effects captured in the ephemeris but not explicitly incorporated in the dynamics model.

Implications

The results indicate that consistency and accuracy represent distinct performance metrics that may not be simultaneously optimized when employing ephemeris-based perturbation modeling. The choice between methods involves trade-offs depending on the mission requirements and the relative importance of internal consistency versus absolute accuracy. The identification of unmodeled forces as the source of method divergence suggests that improved force models or explicit treatment of these effects could potentially reconcile the methods.