Output Feedback Stabilization of an Orbital Robot

In this paper, we propose a novel controller to stabilize the shape (joints) of an orbital robot about a setpoint, i.e. a regulation task, in the specific setting that its spacecraft velocity is unmeasured. For this output feedback stabilization problem, the controller is presented as a synthesis of an observer for the spacecraft's motion states and a shape control law. To this end, we exploit the inertia-decoupled reduced Euler-Lagrange equations. The main advantage of this approach is that the block-diagonal inertia avoids the need for joint acceleration measurements, and the well-partitioned Cori- olis/Centrifugal matrix highlights useful properties, which aid in the stability analysis. Additionally, the proposed controller uses only a minimal set of measurements in form of shape state-space, i.e. positions and velocities, and the exteroceptive pose (attitude and position) of the spacecraft. Thus, the need for inertial sensors (velocity measurements) on the spacecraft is also avoided. For the error dynamics of the resulting system, we prove uniform almost global asymptotic stability. Furthermore, we validate the analysis and prove the effectiveness of the method though simulations.