Modeling, robust control synthesis and worst-case analysis for an on-orbit servicing mission with large flexible spacecraft

TL;DR

This paper presents a comprehensive methodology for modeling and designing robust control systems for on-orbit servicing missions involving large flexible spacecraft, ensuring stability and performance despite uncertainties and dynamic changes.

Contribution

It introduces a novel modeling approach for flexible spacecraft and docking mechanisms, and develops a robust control synthesis method considering all subsystem interactions and uncertainties.

Findings

Successfully modeled the coupled dynamics of chaser and target spacecraft.

Designed a control system that guarantees robustness against uncertainties.

Validated stability and performance through structured singular value analysis.

Abstract

This paper outlines a complete methodology for modeling an on-orbit servicing mission scenario and designing a feedback control system for the attitude dynamics that is guaranteed to robustly meet pointing requirements, despite model uncertainties as well as large inertia and flexibility changes throughout the mission scenario. A model of the uncertain plant was derived, which fully captures the dynamics and couplings between all subsystems as well as the decoupled/coupled configurations of the chaser/target system in a single linear fractional representation (LFR). In addition, a new approach is proposed to model and analyze a closed-loop kinematic chain formed by the chaser and the target spacecraft through the chaser's robotic arm, which uses two local spring-damper systems with uncertain damping and stiffness. This approach offers the possibility to model the dynamical behaviour of a docking mechanism with dynamic stiffness and damping. The controller was designed by taking into account all the interactions between subsystems and uncertainties as well as the time-varying and coupled flexible dynamics. Lastly, the robust stability and worst-case performances were assessed by means of a structured singular value analysis.