## 3 Space Robotics  
Space robotics is the main topic area of nine papers of this Special Issue. In particular, four papers focus on the development and control of free-base robotic systems, three on novel techniques for the attitude control of satellites, one on the wheel odometry of a planetary rover, and another on the proof of concept of a novel exosuit for space activity. The typical application of free-base robotic systems in space is the capture of non-cooperative satellites. In particular, [PERSON] et al. [17] propose a repetitive learning sliding mode stabilization control for a flexible-base, flexible-link and flexible-joint space robot for use to capture a satellite, a process which is validated by a series of dynamic simulations. The system is decomposed into slow and fast subsystems using the singular perturbation theory. To ensure that the base attitude and the joints of the slow subsystem reach the desired trajectories, link vibrations are suppressed simultaneously, and a repetitive learning sliding mode controller based on the concept of the virtual force is designed. Moreover, a multilinear optimal controller is proposed for the fast subsystem to suppress the vibrations of the base and joints. Two sub-controllers constitute the repetitive learning sliding mode stabilization control for the system. This ensures that the base attitude and joints of the system reach the desired trajectories in a limited time after capture, obtain better control quality, and suppress the vibrations of base, links and joints. [PERSON] et al. aimed to address the problem that the joints are easily destroyed by the impact torque during the process of space robot on-orbit capture of a non-cooperative spacecraft. As such, a reinforcement learning control algorithm, combined with a compliant mechanism, is proposed by [18] to achieve buffer compliance control. The compliant mechanism absorbs the impact energy through the deformation of its internal spring, and also limits the impact torque to a safe range by combining with the compliance control strategy. The associative search network is employed to approximate unknown nonlinear functions, and an adaptive critic network is utilized to construct the reinforcement signal to tune the associative search network. The numerical simulation shows that the proposed control scheme can reduce the impact torque acting on joints, by 76.6% at maximum and 58.7% at minimum, in the capturingoperation phase. [PERSON] et al. [19] present the preliminary analysis of a novel lightweight and deployable soft robotic system for space applications that can easily be contained in a relatively small package to be deployed when required. The main challenges for soft robotic systems are the low force exertion and the control complexity. As such, in this work, a soft manipulator concept with inflatable links is introduced to face these issues. A prototype of the inflatable link is manufactured and statically characterized using a pseudo-rigid body model subject to varying levels of inflation pressure. Moreover, the full robot model and algorithms for the load and pose estimation are presented, and a control strategy, using inverse kinematics and an elastostatic approach, is developed. Experimental results provide input data for the control algorithm, and its validity domain is discussed on the basis of a simulation model. The minimization of energy consumption is also of the utmost importance in space robotics. In this context, [PERSON] and [PERSON] [20] present a novel inverse kinematics method for redundant manipulator tracking a desired end-effector trajectory, which is suitable for real-time implementation. The proposed method is based on the optimization of the kinetic energy integral on a limited subset of future end-effector path points, making the manipulator joints move in the direction of minimum kinetic energy. In the simulated tests, the proposed method outperforms the classical pseudoinverse-based solution and proves to be able to avoid singularities.