Dynamics and robust control of a space manipulator with flexible appendages for on-orbit servicing

Space manipulators allow to respond to a variety of problems in future space exploitation and exploration such as on-orbit deployment, active debris removal or servicing operations. However, a difficulty to autonomously control space manipulator systems arise with large and light structures presenting flexible behavior. Flexible dynamics remain a challenging study focus as its modeling may present a first difficulty while the different coupling with the manipulator may deteriorate the control quality. This paper addresses design and control problems related to autonomous space manipulator equipped with kinetic moment exchange devices for spacecraft rotation control when dealing with system internal disturbances, model uncertainties and measurement errors. One advantage of modeling the rigid–flexible dynamics of a multi-body system is the possibility of including the non-measurable states in the system decoupling and linearization. In this work, in addition to the development of an extended state observer (ESO) that estimate the flexible dynamics, a nonlinear disturbance observer (NDO) is also introduced and included in a nonlinear dynamic inversion (NDI) framework where both modeling uncertainties and measurement errors are considered. Inter-dependencies between observers and control dynamics motivate a simultaneous computation of their gains to improve system stability and control performances. This is achieved by the resolution of linear matrix inequalities (LMI). In order to highlight the interest of the proposed scheme and validate our approach in a realistic environment, extensive tests of an on-orbit space telescope assembly use-case are performed on a high-fidelity simulator.