This paper investigates the dynamics modeling and structural optimization of an asymmetric two-stage torsion pendulum designed for drag-free testing in the Taiji mission. This torsion pendulum serves as a critical experimental apparatus for ground-based verification of drag-free control technology in space gravitational wave detection, addressing limitations in dynamic stability and parameter applicability found in traditional testbeds. Using the Lagrangian dynamics method, the equations of motion relative to inertial space are derived and simplified into a linearized dynamics model under the assumption of small-amplitude oscillations. A state-space approach is further employed to analyze the system’s free oscillation behavior, with equilibrium stability rigorously assessed through eigenvalue analysis. Compared to existing approaches, the proposed model significantly enhances computational efficiency and systematically reveals the influence of key structural parameters on system stability. The study identifies critical parameter ranges essential for ensuring system stability, with optimization results demonstrating that proper design and adjustment of structural parameters can substantially improve system robustness and performance. Numerical simulations validate the accuracy of the proposed models and methods, with the optimization scheme showing clear superiority in enhancing system performance and simplifying experimental design. This work establishes a rigorous theoretical framework for ground-based verification of drag-free control technology. It not only effectively addresses bottlenecks in traditional testbed designs but also offers innovative guidance for the development of experimental systems in the Taiji mission.

This paper presents a predefined-time controller for Multiple Space transportation Robots System (MSRS), which can be applied in on-orbit assembly tasks to transport modules to pre-assembly configuration quickly. Firstly, to simplify the analysis and design of predefined-time controller, a Predefined-time Stability Criterion is proposed in the form of Composite Lyapunov Function (CLF-PSC). Besides simplicity, the CLF-PSC also has the advantage of less conservativeness due to utilization of initial state information. Secondly, a concept of Lp-Norm-Normalized Sign Function (LPNNSF) is proposed based on the CLF-PSC. Different from traditional norm-normalized sign function, the Lp-norm of LPNNSF can be selected arbitrarily according to practical control task requirements, which means that the proposed LPNNSF is more generalized and more convenient for calculation. Thirdly, a predefined-time disturbance observer and predefined-time controller are designed based on the LPNNSF. The observer has the property of predefined-time convergence to achieve quicker and more accurate estimation of the lumped disturbance. The controller has less control input and chattering phenomenon than traditional predefined-time controller. In addition, by introducing the observer into the controller, the closed-loop system enjoys high precision and strong robustness. Finally, the effectiveness of the proposed controller is verified by numerical simulations. By employing the controller, the MSRS can carry assembly modules to the desired pre-assembly configuration accurately within predefined time.

This paper presents Part Ⅱ of a review on DFACS, which specifically focuses on the modeling and analysis of disturbances and noises in DFACSs. In Part Ⅰ, the system composition and dynamics model of the DFACS were presented. In this paper, we discuss the effects of disturbance forces and noises on the system, and summarize various analysis and modeling methods for these interferences, including the integral method, frequency domain analysis method, and magnitude evaluation method. By analyzing the impact of disturbances and noises on the system, the paper also summarizes the system’s performance under slight interferences. Additionally, we highlight current research difficulties in the field of DFACS noise analysis. Overall, this paper provides valuable insights into the modeling and analysis of disturbances and noises in DFACSs, and identifies key areas for future research.

The Drag-Free and Attitude Control System (DFACS) is a critical platform for various space missions, including high precision satellite navigation, geoscience and gravity field measurement, and space scientific experiments. This paper presents a comprehensive review of over sixty years of research on the design and dynamics model of DFACS. Firstly, we examine the open literature on DFACS and its applications in Drag-Free missions, providing readers with necessary background information on the field. Secondly, we analyze the system configurations and main characteristics of different DFACSs, paying particular attention to the coupling mechanism between the system configuration and dynamics model. Thirdly, we summarize the dynamics modeling methods and main dynamics models of DFACS from multiple perspectives, including common fundamentals and specific applications. Lastly, we identify current challenges and technological difficulties in the system design and dynamics modeling of DFACS, while suggesting potential avenues for future research. This paper aims to provide readers with a comprehensive understanding of the state-of-the-art in DFACS research, as well as the future prospects and challenges in this field.

Air-breathing hypersonic vehicle has great military and potential economic value due to its characteristics: high velocity, long range, quick response. Therefore, the development of hypersonic vehicle and its guidance and control technology are reviewed in this paper. Firstly, the development and classification of hypersonic vehicles around the world are summarized, and the geometric configuration and mission profile of typical air-breathing hypersonic vehicle are given. Secondly, the control difficulties of air-breathing hypersonic vehicle are introduced, including integrated design of engine and fuselage, static instability, strong nonlinearity, uncertain aerodynamic parameters, etc. According to its control requirements, the control methods considering external disturbance, fault-tolerant control methods, anti-saturation methods, and prescribed performance control methods considering transient performance constraints are summarized respectively. The classification and comparison of various control methods are given, and the frontiers of theoretical development are analyzed. Finally, considering the effects of composite disturbances, the design of terminal guidance law under multiple constraints is overviewed, including guidance law with angle constraint, velocity constraint, acceleration constraint and time constraint. Similarly, the classification of guidance law design methods under different constraints, their advantages as well as the future development trend and requirements are introduced.