Simultaneous Motion Replanning and Gravity Model Refinement near Small Solar System Bodies

Abstract

Strategic missions to orbit celestial bodies have primarily considered spacecraft trajectories as a two-step process: capture of the spacecraft within the gravitational influence of the body, followed by in-orbit maneuvers. Moreover, a priori maneuver planning approaches using Earth-based measurements tend to generate motion plans that have little scope of replanning, especially when the spacecraft is in the body’s vicinity. Fine-grained motion plans that respond to mission conditions require a detailed understanding of the gravitational forces around the body, which can provide essential information about the body. Our research focuses on a problem variant where the orbital maneuvers are designed to continually refine the onboard gravitational model of the body while simultaneously using the model to perform increasingly smoother orbital maneuvers. We develop a receding horizon approach. Starting with a (low-fidelity) gravity model created from Earth-based observations, the gravity model is continually updated as the spacecraft experiences varying gravitational forces. The updated model is simultaneously and continually used to replan the craft’s trajectory, ensuring that successive maneuvers respect the most up-to-date gravity model. The motion plan eventually attains a near-stable orbital motion. Such an approach has the potential to expand to autonomous missions to improve the mapping and exploration of smaller bodies.