Simulation of robotic space operations with minimum base reaction manipulator

Autonomous robotic capture has been identified as a key technology for On-Orbit Servicing (OOS) and Active Debris Removal (ADR) missions. However, manoeuvring spacecraft-mounted manipulators is a challenging task since it generates disturbance torques on the satellite. To mitigate this problem several minimum reaction control strategies have been developed to reach the desired End-Effector (EE) pose while minimizing the dynamic disturbances transferred to the spacecraft by the robotic arm. This paper presents the development of a Simulation Tool in the MATLAB/Simulink environment capable of simulating the dynamics of a satellite equipped with a 7-DoF robotic arm during the target capture phase. The manipulator, as well as the spacecraft, is implemented by using Simscape Multibody and joint actuators are modelled as Brushless DC motors controlled by PID controllers. The spacecraft attitude is Nadir-Pointing, it is controlled by means of quaternion feedback and Linear-Quadratic-Regulator (LQR) and it is actuated by three Reaction Wheels (RW). Orbital perturbations such as non-spherical gravity potential (EGM2008 model) and atmospheric drag are considered. In addition, the minimum reaction control strategy called Kinetic Energy Minimization (MKE) is employed during the robotic arm manoeuvres. The goal of this study is to compare the performances obtained with the MKE method with those achieved by using the classic Inverse Kinematics (IK) in the free-flying case. The numerical results confirmed that MKE method is to be preferred since it minimizes the control torque that the Attitude Control Subsystem (ACS) must provide and reduces the EE orientation and position errors.