  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.

Systems and Control;Systems and Control