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.

Non-gravitational force models are critical not only for the applications of satellite orbit determination and prediction, but also for the studies of gravitational reference sensors in space-based gravitational wave detection missions and accelerometers in gravity satellite missions. In this paper, based on the inertial sensor data from the TianQin-1 (TQ-1) mission, a correction has been made in the non-gravitational force models by applying additional terms related to the orbital periods. After taking into account this correction, about 37 hours of TQ-1 inertial sensor data is calibrated in the sensitive axes, i.e. y- and z-axes, by comparing with the simulated non-gravitational accelerations. It is indicated that the peak-to-peak value of the non-gravitational acceleration correction terms are about 2% and 13% of the measured accelerations in the y- and z-axes, respectively. Within the frequency band below 0.01 Hz, the root mean square of calibration residual errors in y- and z-axes are suppressed from 1.03 × 10⁻⁹ and 3.872 × 10⁻⁹ m s⁻² to 8.14 × 10⁻¹⁰ and 1.343 × 10⁻⁹ m s⁻², respectively. The bias and scale factor of the inertial sensor are also obtained from the calibration by the method of least-squares fit. Meanwhile, the inertial sensor measurements are validated and their signal compositions are analyzed.

High-energy particles in space will inevitably penetrate the spacecraft into the suspended test mass, which would seriously affect the detection of gravitational waves; therefore, charge measurement and control are essential. Based on the working principle of space inertial sensors, this article proposes a new charge measurement scheme based on capacitive sensing in nonsensitive axes for simultaneous charge measurement during the detection of gravitational waves. According to the dynamic model and actual parameters, the resolution of the proposed method is evaluated as about $6.60\times 10^{-17}$ C in space, which can meet the detection requirement. Further, a torsion pendulum device was set up on ground to carry out charge measurement experiments and verify the evaluation method. The experimental results show that the optimal resolution with the capacitive sensing is about $1.65\times 10^{-14}$ C at 1 mHz, which agrees with the theoretical evaluation. This work demonstrates the feasibility of the capacitive sensing-based charge measurement, which will be a potential scheme in the detection of gravitational waves.

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.