A Gravity Compensation System for Touchdown Process Verification of Large Spacecraft With Quasi-Zero Stiffness Mechanism and Passivity-Based Controller

To ensure the reliability of an extraterrestrial lander during its touchdown process, it is crucial to replicate the landing dynamics within a simulated low-gravity environment. In this study, a servo-driven system(SDS) is proposed and integrated with a quasi-zero stiffness(QZS) system to address the limitations of traditional methods, including restricted accuracy and limited movement range. An analytical method for describing the dynamic characteristics of the low-gravity simulation system is presented based on passivity theory, enhancing the compensation accuracy. Subsequently, a fuzzy controller for the QZS-SDS composite system is designed to autonomously adjust the equilibrium point and convergence speed, ensuring rapid error reduction in tension control. Furthermore, the global asymptotic stability conditions of the closed-loop system are established and analyzed, and the quantitative parameter design guidelines for practical implementation are provided. Finally, a series of physical experiments demonstrate the efficiency and robustness of the proposed system. Compared to conventional methods using only QZS, the proposed approach reduces the maximum force compensation error from 13.9% to 4.0%, and extends the supported simulation range from 800mm to over 12,000mm. Note to Practitioners—This study addresses the challenges of providing a reliable low-gravity environment for the touchdown phase of extraterrestrial landers. The primary motivation is to verify the robustness of the engine shutdown algorithm and evaluate the strength/stiffness design of the landing legs under realistic impact conditions. While some low-gravity compensation systems have been widely used in orbiting and descent phases, their effectiveness during the touchdown process, where strong impacts occur, remains insufficiently explored. At higher landing velocities(approximately 1.1 m/s), most low-gravity compensation systems struggle to maintain accuracy due to bandwidth limitations, except for quasi-zero stiffness(QZS) systems. However, QZS-based approaches suffer from mechanical deviations such as stiffness inconsistencies in energy storage components and friction, leading to reduced compensation accuracy. Additionally, the movement range of QZS is constrained by mechanical structures, restricting their application in spacecraft landing missions. To overcome these limitations, we propose an actively controlled servo-drive system with a passivity-based control law for precise force compensation. The introduction of servo motors not only improves compensation accuray but also significantly extends the system’s operational range, enabling it to meet the requirements of various landing tasks. This work has direct implications for practitioners developing ground-based low-gravity simulation systems for extraterrestrial exploration. In the future, we aim to extend our low-gravity compensation technology to support extraterrestrial launch missions, broadening its application from single-degree-of-freedom landing tasks to multi-degree-of-freedom non-vertical take-off scenarios.