HILS Verification of MPC of Rotation Floating Space Robot (RFSR) for Fine Manipulation

Model Predictive Control of Floating Space Robots for Close Proximity On-Orbit Operations

Autonomous space robots are and will be essential for future space missions like on-orbit satellite servicing, on-orbit assembly, active debris removal etc. Such missions require a base satellite equipped with deft manipulators for the on-orbit tasks. Such manipulator equipped space robots combine the non-linearities of ground based robots with the complexities of the control architectures of space systems. Manipulator motion induces reaction forces and moments on the satellite which tend to disturb its position and attitude, in turn affecting the end-effector pose. Lack of a fixed base thus arises serious problems in controlling the space manipulators for precision tasks like capture of a space debris or on-orbit servicing tasks. The dynamical interaction between the manipulator and the base satellite must therefore be taken into consideration while designing a control law for space manipulators. We have, in our previous works, proposed a Nonlinear Model Predictive Controller (NMPC) for the control of a planar floating space robot. However, three dimensional simulation of such floating space robots with sophisticated robotic arms is difficult due to the high degree of freedom of the combined system. This leads to complicated and large dynamics which is difficult to solve. Secondly, a simulation environment is essential for depicting the contact dynamics between the end-effector of the space robot and the target object in-orbit. This paper thus proposes a Model Predictive Controller (MPC) based control law for the simulation of three dimensional floating space robots in PyBullet environment. We also simulate the contact dynamics when the gripper mounted on the end-effector grabs the target and the combined system is then re-oriented to attain the initial configuration of the arm. The simulation thus shows the complete workflow from the time the robotic arm is deployed till the target is successfully captured or docked on to.