Spaceborne gravitational wave detectors achieve long-baseline inter-satellite laser interferometry through satellite constellations, overcoming the limitations imposed by seismic noise and interferometer arm lengths on ground-based detectors, and providing a new observational means for detecting medium- and low-frequency gravitational waves and revealing the origin and evolution of the universe. The TianQin project aims to build a high ‑precision spaceborne gravitational wave detection array. The test mass within its core component, the gravitational reference sensor, must transition smoothly from a high-load locked state to an ultra‑quiet and ultra‑stable geodesic state after launch and orbit injection, and this release process is a critical link for mission success. However, the plunger of the grabbing, positioning, and release mechanism (GPRM), under prolonged high-load operation, induces adhesion effects such as cold welding on the test mass, and the available electrostatic capture force is insufficient to overcome the interfacial adhesion, making it difficult for conventional release strategies to meet the strict constraint of residual velocity below 5 μm/s. Therefore, establishing a theoretical model that can accurately describe the dynamic behavior of the release mechanism and the interfacial adhesion effect is of great significance for evaluating release performance, revealing the mechanism of residual velocity generation, and guiding the optimization of mechanism parameters.
In a recent study published in Space: Science & Technology , the team led by Associate Professor Xue Chao from the School of Physics and Astronomy at Sun Yat-sen University, in collaboration with the team led by Professor Zhang Jinxiu from the School of Aeronautics and Astronautics, addressed the key issues in the test mass release process for spaceborne gravitational wave detection. They established a dynamic model of the release mechanism, a rough-surface contact force model, and a comprehensive dynamic model of the test mass release process. They proposed a parameter identification method based on an improved genetic algorithm and completed model parameter identification using experimental data, and further conducted a parametric sensitivity analysis. The results show that the improved genetic algorithm-based identification method significantly enhances the model approximation, enabling the model to accurately describe the dynamic behavior during release. Under adhesion, the test mass in the unilateral release scenario achieved a residual velocity far below 5 μm/s, confirming that adhesion is not the primary factor causing excessive residual velocity. The parametric sensitivity analysis revealed that the test mass residual velocity is highly sensitive to the energy exchange ratio of the piezoelectric stack and the stiffness of the disk spring. This study provides an important theoretical basis for performance evaluation, parameter selection, and control design of the test mass release mechanism for spaceborne gravitational wave detectors, and holds significant engineering guidance value for advancing the development of space-based gravitational wave detection missions such as TianQin.
The study focuses on the dynamic modeling requirements for the test mass release process in spaceborne gravitational wave detection and establishes an electromechanical coupling dynamic model of the release mechanism. In spaceborne gravitational wave detection missions, the test mass must be firmly locked during the launch phase and then smoothly released into an ultra ‑quiet and ultra-stable geodesic state after orbit injection. This process directly affects the measurement accuracy of the gravitational reference sensor. The core working principle of the release mechanism is illustrated in Fig. 1. Initially, the piezoelectric stack is energized to extend the release tip and press it against the test mass. Upon release, the piezoelectric stack is instantaneously short-circuited through a discharge resistor, causing the release tip to retract rapidly. The inertia of the test mass then overcomes the interfacial adhesion between the release tip and the test mass, achieving separation. Based on the actual motion states and observability of the mechanism components, the release mechanism was discretized into two equivalent mass blocks. Using Newtonian dynamics, Kirchhoff's circuit laws, and the piezoelectric constitutive equations, a dynamic relationship between the voltage input and the displacement of the release tip was established, providing a theoretical foundation for subsequent system identification and interfacial force analysis.
Secondly, to address the difficulty of directly measuring key parameters in the dynamic model, the study proposes a parameter identification method based on an improved genetic algorithm and establishes an interfacial contact force model that accounts for surface roughness using the Johnson ‑Kendall‑Roberts (JKR) theory. To overcome the classic genetic algorithm’s tendency toward premature convergence and local optima, the study employs adaptive crossover and mutation probabilities along with a diploid gene strategy, as illustrated in Fig. 2. The dataset required for parameter identification was obtained by measuring the release tip displacement with a fiber-optic laser encoder and the voltage across the piezoelectric stack with a high‑voltage differential probe, as shown in Fig. 3. Compared with the classic algorithm, the improved algorithm reduces the maximum residual and average residual by 48.17% and 6.04%, respectively, significantly enhancing the model approximation. On this basis, the study accounts for the surface roughness of the contact interface between the release tip and the test mass and develops an adhesion contact model for rough surfaces based on JKR theory. As depicted in Fig. 4, the rough surface is modeled as an array of asperities whose heights follow a normal distribution, and the total contact force is obtained by integrating the contributions of all asperities, yielding the relationship between contact force and interface distance. This interfacial contact force model can describe both compressive and tensile adhesion states, providing a critical input for the subsequent dynamic analysis of test mass release.
Finally, the study analyzed the velocity response of the test mass under unilateral release conditions through numerical simulation and discussed the influence of mechanism parameters on the test mass residual velocity. As shown in Fig. 5, during the separation process, the interfacial contact force gradually transitions from compression to adhesion tension and eventually approaches zero, with a maximum adhesion force of approximately 6 mN, consistent with the millinewton ‑level results reported in previous studies. Under the unilateral release scenario considering only adhesion, the test mass velocity gradually increases and approaches a stable value, as shown in Fig. 6. The calculated residual velocity of the test mass is approximately 0.04 μm/s, far below the mission requirement of 5 μm/s, indicating that the adhesion between the release tip and the test mass is not the primary factor causing excessive residual velocity. To investigate the influence of mechanism parameters on release performance, the study further analyzed the sensitivity of the test mass residual velocity to various parameters. The results show that the residual velocity is most sensitive to the energy exchange ratio T em and the disk spring stiffness k p , increasing with T em and decreasing with k p . The study suggests that using a piezoelectric stack with a lower energy exchange ratio or a disk spring with higher stiffness can reduce the test mass residual velocity and thus improve release mechanism performance. This dynamic model provides important theoretical support and design guidance for the engineering development and optimization of the test mass release mechanism for spaceborne gravitational wave detectors.