The TianQin-1 satellite (TQ-1), which is the first technology demonstration satellite for the TianQin project, was launched on 20 December 2019. The first round of experiment had been carried out from 21 December 2019 until 1 April 2020. The residual acceleration of the satellite is found to be about 1 × 10 ⁻¹⁰ m/s ² /Hz ^1/2 at 0.1 Hz and about 5 × 10 ⁻¹¹ m/s ² /Hz ^1/2 at 0.05 Hz, measured by an inertial sensor with a sensitivity of 5 × 10 ⁻¹² m/s ² /Hz ^1/2 at 0.1 Hz. The micro-Newton thrusters has demonstrated a thrust resolution of 0.1 μ N and a thrust noise of 0.3 μ N/Hz ^1/2 at 0.1 Hz. The residual noise of the satellite with drag-free control is 3 × 10 ⁻⁹ m/s ² /Hz ^1/2 at 0.1 Hz. The noise level of the optical readout system is about 30 pm/Hz ^1/2 at 0.1 Hz. The temperature stability at temperature monitoring position is controlled to be about ±3 mK per orbit, and the mismatch between the center-of-mass of the satellite and that of the test mass is measured with a precision of better than 0.1 mm.

Capacitive sensing electronics are critical to space gravitational wave detection missions, providing the test mass motion information for the inertial sensor’s non-sensitive axis control and the drag-free control of the satellite. For the TianQin mission, the capacitive sensor requirement is 6.9 × 10 − 7 p F H z − 1 / 2 at 6 mHz, corresponding to a displacement noise of 1.7 n m H z − 1 / 2 . This paper presents the system design scheme, noise analysis, and performance testing of the capacitive sensor for the TianQin mission. Based on the previous work of our group, a capacitive sensing scheme based on a transformer bridge and modulation–demodulation is adopted. A transformer with a better high LQ product is fabricated, and the preamplifier current noise is reduced to further improve the performance above mHz. The amplitude stability of the AC carrier and the performance of the lock-in amplifier circuit are further improved to reduce the low-frequency 1 / f noise at m H z and below. Finally, a capacitive sensor prototype is developed and tested, the experimental results show that the capacitance measurement noise is better than 3 × 10 − 7 p F H z − 1 / 2 above 1 mHz and better than 6 × 10 − 7 p F H z − 1 / 2 at about 0.1 mHz , which meets the overall performance requirement of the TianQin mission.

Drag-free control (DFC) is one of the key technologies for space-borne gravitational wave detectors. For the TianQin (TQ) project, non-gravitational disturbances on the spacecraft must be suppressed by DFC. TianQin-1 (TQ-1) is the first satellite for technology verification, whose main goal is to verify the disturbances reduction technologies. In this paper, the DFC requirement and preliminary analysis for the TQ project are introduced, and then the design and the experimental validation with the TQ-1 satellite is presented. In-orbit results show a successful validation of DFC and the residual acceleration of TQ-1 satellite has been suppressed to 5 × 1 0 − 11 m s − 2 H z − 1 / 2 at 10 mHz versus 2 × 1 0 − 9 m s − 2 H z − 1 / 2 thruster noise.

High-precision electrostatic accelerometer has been widely employed in gravity measurement satellites. Accelerometer can be designed for different resolutions and measurement ranges to adapt to different scientific missions. This paper presents an ultra-high sensitivity 70 g-TM electrostatic accelerometer, designed to achieve an adjustable resolution from 10 − 12 m s − 2 Hz − 1 / 2 to 10 − 10 m s − 2 Hz − 1 / 2 with an optimal resolution of 3.3 × 10 − 12 m s − 2 Hz − 1 / 2 . The in-orbit performance of the 70 g-TM accelerometer was tested on the Tianqin-1 satellite.

Inertial sensor (IS) is one of the most critical units in space-based gravitational wave detection projects. Any actuation to sensing crosstalk in the IS might lead to operational anomalies in sensing electronics, thereby affecting the closed loop control of the test mass. The theoretical model for the crosstalk has been analyzed and verified. A secondary-tuning method is proposed to suppress the actuation to sensing crosstalk. Considering the influence of the circuit’s stray capacitance which acts as the equivalent primary resonance tuning capacitance, experimental results indicate that the secondary-tuning method could attenuate the crosstalk factor by 5, compared to the traditional primary-tuning method. The actuation to sensing crosstalk is reduced, and then the measurement accuracy of the displacement sensor is relatively improved. Based on the theoretical crosstalk model, the criteria for selecting the basis function waveform of the feedback voltage are provided. When the basis function of the feedback voltage is selected to be a 150 V sinusoidal signal, the primary-tuning method requires a frequency of less than 337 Hz, while the secondary-tuning method allows for a frequency of less than 528 Hz according to the experimental results. The requirement for the feedback voltage frequency in the secondary-tuning method has been relaxed nearly by a factor of 1.5, which allows for large frequency intervals and could suppress the coupling between the actuator’s degrees of freedom.

Capacitive displacement transducers play a crucial role in inertial sensors especially for space gravitational wave detection missions. One of the major requirements for the displacement transducer is to have a lower sensing offset. The sensing offset will adversely affect the accuracy of the absolute position measurement of the test mass, providing erroneous data to the drag-free controller and leading to spacecraft mispositioning. Additionally, the offset could introduce multiplicative noise to the sensing output and the closed loop output of the inertial sensor. The asymmetry of the sensing bridge within the front-end electronics has been identified as the primary source of these offsets. This paper analyzes the requirements of the main parameters in the sensing bridge. A method is proposed to reduce the sensing offset by utilizing differentiated resonant capacitors while maintaining the ability to tune the resonant frequency and ensure a sufficiently low sensing noise level. Experimental results show that this approach can effectively reduce the residual sensing offset to (−15.7 ± 5.0) ppm, which satisfies the stringent requirement for space inertial sensors in the TianQin mission.