TianQin is a future space-based gravitational wave (GW) observatory targeting the frequency window of 10⁻⁴–1 Hz. A large variety of GW sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about 10⁵ km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ‘0123’ technology roadmap. In step ‘0’, the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ‘1’, the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ‘2’, the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ‘3’, i.e. the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based GW detector, TianQin, and to start GW detection in space.

The high-precision gravitational reference sensor, which hosts a heavy test mass (TM) surrounded by electrodes with a relatively large gap, is crucial in all high-sensitivity drag-free sensors. Consequently, a dedicated locking mechanism is needed to securely hold the TM during the launch phase. After reaching the intended orbit, the TM is released to a free-falling state and subsequently captured by electrostatic actuation, which demands that the transferred momentum and angular momentum to the TM do not exceed ${10}^{-5}\mathrm{kgm}/\mathrm{s}$ and ${10}^{-7}{\mathrm{kgm}}^2/\mathrm{s}$, respectively. This paper introduces a three-level structural design of the locking-and-release mechanism. In order to investigate the release requirement, a pendulum system has been developed for on-ground testing. The mock-up of the TM is entirely consistent with the size and mass of TianQin TM, and the dual-sided release tips constrain the TM and then rapidly retract simultaneously, after which the transferred momentum and angular momentum are estimated from the free oscillations as $0.38\left(21\right)\times {10}^{-5}\mathrm{kgm}/\mathrm{s}$ and $0.15\left(14\right)\times {10}^{-7}{\mathrm{kgm}}^2/\mathrm{s}$ with a preload force of 0.3 N. This proposes a feasible scheme for validating the release mechanism conducting impulse testing for the TianQin project.

Capacitive transducers are widely used in fundamental physics experiments, seismology, Earth or planetary observations, and space scientific and technical applications because of their high precision, simple structure, and compatibility with various measurements. However, in real applications, there is a trade-off between their resolution and dynamic range. Therefore, this paper is aimed at enlarging the dynamic range while ensuring high resolution. In this paper, a noise analysis of a capacitive transducer is presented, which shows that the amplitude noise of the carrier wave is the main limiting factor. Hence, a new method of generating a carrier wave with lower-amplitude noise is proposed in the paper. Based on the experimental verification, it is found that the carrier wave produced through the new method performed significantly better than the typical digital carrier wave when they were compared in the same sensing circuit. With the carrier wave produced through the new method, the dynamic range of the capacitive transducer can reach 120.7 dB, which is 18.3 dB greater than for the typical direct digital synthesis (DDS) method. In addition, the resolution of the carrier wave is mainly limited by the voltage reference components.

Due to the excellent sensitivity for small torque, torsion pendulums are widely used. The thermal noise is a fundamental limit according to the fluctuation–dissipation theorem. The damping induced by the eddy current has been well studied, but it has not been verified directly whether the eddy current generates the Brownian motion in accordance with the fluctuation–dissipation theorem for a macroscopic pendulum. In this work, we verify the Brownian motion induced by the eddy current using torsion pendulums in the geomagnetic field. For a hollow cube aluminum pendulum with a side length of 50 mm and thickness of 1 mm, the measured torque noise is about 1×10−15Nm/Hz, consistent with the thermal noise predicted by the eddy current in a 60.5 μT ambient magnetic field. By applying the magnetic shield for a disk-shaped pendulum, the torque noise is improved to 1×10−16Nm/Hz and reaches the thermal noise limit with quality factor Q = 4.3 × 105.

The surface of the coating or substrate structure has a rough topological structure over multiple scales, which significantly affects the actual contact area and adhesion strength. In order to investigate potential interferences during the test mass (TM) release process of the locking and release mechanism in TianQin space-borne gravitational wave detection project, an analytical model of the Johnson–Kendall–Roberts (JKR) adhesive contact with coating roughness between the TM and the release tip has been developed. This work presents the integration of the JKR theory with the Greenwood–Williamson rough surface contact theory to address adhesion challenges and influence of roughness in space-borne gravitational wave detection systems. The comprehensive model can be used to analyze how various factors such as surface shape, material properties, coating thickness and roughness affect adhesion. By introducing a numerical approach based on the Newton down-hill method to solve coupled equations for gap, stress, and load balance, the model achieves high-precision predictions of adhesion behavior under multi-scale roughness effects. By establishing relationships between force, contact half-width, and penetration depth, it provides a theoretical basis for optimizing the TM release process and the design of the locking and release mechanism. Future work will validate predictions via high-precision torsion pendulum experiments.

The gravitational constant G was the second fundamental constant to be measured. However, it exhibits the lowest measurement precision among all fundamental physical constants. The latest CODATA-2022 recommended value of G is 6.67430(15)×10⁻¹¹m³kg⁻¹s⁻², with a relative standard uncertainty of 22 ppm. Over the past two centuries, the precision of G measurements has increased by only approximately three orders of magnitude. In this article, we first introduce the historical development of G measurements. Next, we compare the determinations of G obtained using different methods and instruments across various experimental setups, analyzing their respective advantages and disadvantages. Finally, we briefly discuss the temporal variation of G and the error sources in measurement of G.