Dynamic test of the continuously variable weak force by a torsion pendulum with pre-applied stress

High-precision, continuously variable weak force testing is required for high-precision drag-free control with micro-thrust of spacecrafts, which is a key technology for space gravitational wave detection programs, such as TianQin, LISA, and Taiji. The continuously variable micro-thrust range is 0.1∼100μN, and the noise is below 0.1 μNHz−1/2 from 10−4Hz to 1 Hz. The torsion pendulum is considered as the most classical weak force measurement tool. However, the large response of non-sensitive modes makes it unsuitable for dynamic weak force measurements. In this study, a dynamic test system is developed for continuously varying weak forces using a torsion pendulum. We pre-applied a stress to the torsion pendulum using a double wire structure, which can effectively reduce the interference of other modes, and used feedback control to improve the stability. The evaluation results obtained using the external continuously variable electrostatic force indicate that the measurement range of the system covers 100 μN, the response time is approximately 1.6 s, and the noise is below 0.1 μNHz−1/2 from 0.9×10−4Hz to 1.4 Hz, which can meet the requirements of the micro-thrust test in space gravitational wave detection missions. •A torsion pendulum with pre-stress enhances the non-sensitive directional stiffness.•Using the system dynamic response function to evaluate the weak force performance.•The results meet the requirements of space-borne gravitational wave detection.