## 1 Introduction  
Space manipulators are a crucial component of space exploration missions due to their ability to perform a wide range of tasks in space. Many studies have focused on various aspects of space manipulator design, such as dynamic modeling, kinematics and dynamics analysis, and control strategies. Semiautonomous teleoperation based on learning from demonstration is an effective method of remote operation of space manipulators, particularly in scenarios with limited communication and repeated operation problems [1]. The control of space manipulators has its own characteristics and testing methods due to the unique working environment of space. In this regard, a hybrid mapping method using an exoskeleton device and surface electromyography sensors has been proposed for manipulator teleoperation [2]. A non-equidistant fractional-order accumulation (NEEA) model of a visual-based space manipulator that uses a modified extrapolation method to predict the trajectory of a motion target floating in outer space has been presented [3]. Collectively, these studies demonstrate the importance of space manipulators for space exploration and highlight ongoing research efforts to improve their capabilities and performance. To further enhance the performance of space manipulators, ground-based experiments and testing are essential. These tests are typically conducted in a controlled environment and allow researchers to simulate and evaluate different scenarios, such as the effects of gravity and other environmental factors on the manipulator's performance. One area of focus in ground-based testing of space manipulators is gravity compensation. This involves developing techniques to offset the effects of gravity on the manipulator and maintain its position and orientation in space. The success of space missions relies heavily on the performance and reliability of space manipulators, and ground-based testing plays a critical role in ensuring their success. Due to the fact that space manipulator design work is carried out in a zero-gravity environment, the weight of the manipulator itself will have a significant impact on its movement during ground testing. The torque generated by gravity on the joints of the manipulator may even exceed the mechanical load range, making it impossible for the manipulator to perform certain actions. Several studies have contributed to the development of effective test systems for space manipulators and improve our understanding of their control mechanisms. To achieve efficient assembly, time-optimal trajectory planning based on the genetic algorithm is utilized, and the feasibility of the proposed method is verified through preliminary ground experiments of assembling submirror modules of space telescopes using the KUKA LWR iwa-7 [4]. A novel active gravity compensation concept has been proposed to simulate space on-orbit microgravity environments for free-flying robots [5] on the ground. Dynamic requirements for designing ground manipulator platforms that can be utilized to verify the performance of the controllers developed for space manipulators are realized [6]. New projects have also been implemented for environmental testing of space robotic arms [7]. Passive gravity compensation and active gravity compensation are the two main methods used in ground-based testing of space manipulators. Passive gravity compensation is achieved by using pulleys and weights to balance the gravity of the manipulator. The advantage of this method is that it provides stable static gravity balance, but its disadvantage is that the additional inertia generated by the weights during the movement of the manipulator can affect the testing results. In contrast, active gravity compensation is achieved by using specially designed actuators to actively control the force applied to the manipulator and maintain a balance between the gravity and the applied force, which is measured by force sensors.