In this study, an active microvibration isolation system is developed for precision space payload. Vibrational environment affects the performance and reliability of measuring instruments. To improve the measurement accuracy of the precision space payload, an active vibration isolation system based on eight vibration isolation modules, which are applied for microvibration isolation on the satellite, is designed. A vibration suppression control strategy for multiple degrees of freedom is studied. A hybrid control method involving a feedback and a feedforward controller based on a nonlinear tracking differentiator and an nth-order weak integrator, respectively, was adopted to optimize the suppression effect of microvibration. As a result, the microvibration of the order of mg can be reduced to the order of μg through the active control of modules. Research experiment results show that the root cumulative power spectral density of the systemic sensitive frequency band in the range of 0.5–200 Hz, i.e., microvibration frequency band in the optical reference cavity, has been reduced to in the order of μg in three directions, which satisfied the requirements of aerospace engineering.

The optical reference cavity in an ultrastable laser is sensitive to vibrations; the microvibrations in a space platform affect the accuracy and stability of such lasers. In this study, an active vibration isolation controller is proposed to reduce the effect of vibrations on variations in the cavity length and improve the frequency stability of ultrastable lasers. Based on the decentralized control strategy, we designed a state-differential feedback controller with a linear quadratic regulator (LQR) and added a disturbance observer (DOB) to estimate the source noise. Experiments were conducted using an active vibration isolation system; the results verified the feasibility and performance of the designed controller. The accelerations along the axis (Z-, X-, Y-) directions were suppressed in the low-frequency band within 200 Hz, and the root-cumulative power spectral densities (PSDs) declined to 1.17 × 10⁻⁵, 7.16 × 10⁻⁶, and 8.76 × 10⁻⁶ g. This comprehensive vibration met the requirements of an ultrastable laser.

To detect low-frequency gravitational waves, it is necessary to eliminate the interference of geo-noise and build a laser interference gravitational-wave detection device in space. Space gravitational-wave detection missions, namely Taiji, LISA, and Tianqin, have been planning to achieve picometer sensitivity on an interferometer arm of several million kilometers to meet the gravitational-wave detection requirements. Because of the orbit evolution and the time delay in interferometer arms, the direction of the transmitted laser beam changes; consequently, a remote telescope cannot receive the laser beam to complete the inter-satellite laser interference. In this study, a two-dimensional point-ahead angle mechanism (2DPAAM) is designed and demonstrated to solve the aforementioned problem. Based on the design concept of aligning the rotation center with the mirror surface center, the 2DPAAM employs a four-link flexible-hinge structure, length expanding and contracting piezoelectric stack actuators, and closed-loop control of capacitive sensors to realize two-dimensional picometer-stable, high-precision rotation. A static model is established to analyze the rotational characteristics, and finite element analysis is performed to study the mechanical properties and to verify the rotational characteristics. The yaw and pitch stiffness errors are ∼0.93% and 5.9%, respectively, when the theoretical results are compared with the simulation results. A series of experiments are conducted on the developed 2DPAAM, and the results show that the rotary ranges of yaw and pitch motions attain ±270 and ±268 µrad, respectively. The rotational accuracies of both yaw and pitch motions attain ∼0.35 µrad, and the optical path difference is less than 10pm/Hz when the frequency is between 1 mHz and 1 Hz, by analogy.

In space gravitational wave detection, the inter-satellite link-building process requires a type of steering mirror to achieve point-ahead angle pointing. To verify that the background noise does not drown out the gravitational wave signal, this paper designed a laser heterodyne interferometer specifically designed to measure the optical path difference of the steering mirror. Theoretically, the impact of angle and position jitter is analyzed, which is called tilt-to-length (TTL) coupling. This interferometer is based on the design concept of equal-arm length. In a vacuum (${10}^{-3} \mathrm{P}\mathrm{a}$), vibration isolation (up to 1 Hz), and temperature-controlled (approximately 10 mK) experimental environment, the accuracy is increased by about four orders of magnitude through a common-mode suppression approach and can reach $390 \mathrm{p}\mathrm{m}/\sqrt{\mathrm{H}\mathrm{z}}$ when the frequency is between 1 mHz and 1 HZ. By analogy, the optical path difference caused by the steering mirror reaches $5 \mathrm{p}\mathrm{m}/\sqrt{\mathrm{H}\mathrm{z}}$ in the 1 mHz to 1 Hz frequency band. The proposed TTL noise model is subsequently verified.

In the detection of gravitational waves in space, during the science phase of the mission, the point ahead angle mechanism (PAAM) serves to steer a laser beam to compensate for the angle generated by the relative motion of the two spacecrafts (SCs) during the approximately 10 seconds of flight time a laser beam will take from one SC to reach a distant SC of three million kilometers away. The common practice for pointing stability control of a laser beam is to first do a coarse tracking by the PAAM to steer a laser beam to compensate for the relative motion between two SCs and to be followed by a fine pointing stability control. In the present work, by exploiting the near-circular orbit structure of an individual SC in the triangular constellation, the feasibility of inserting an adaptive extended Kalman filter (AEKF) into the PAAM control loop is investigated. By adopting a colored measurement noise model that closely resembles the prospective on an orbit situation, numerical simulation suggests that the dynamic range of the PAAM may be reduced to the level of nanoradians using the prediction of the pointing head angle by the AEKF. This will cut down on the tilt-to-length (TTL) coupling noise and the position noise budget allocated to the PAAM. This in turn reduces the dynamic range of the fine pointing control and leaves room to improve its accuracy, thereby offering the prospect of reduction of the position noise budget allocated to the laser pointing instability as a whole.

Low-frequency base vibration transmitted through supporting platforms can degrade the stability of precision payloads, optical instruments, and inertial measurement systems. In velocity-sensor-based active isolation platforms, displacement-related feedback states are unavailable. Direct velocity integration can drift under sensor bias, while raw lower-platform velocity feedforward can introduce measurement noise and out-of-band components. This paper proposes a dual extended state observer (ESO) reconstruction method combining equivalent-displacement feedback and lower-platform feedforward. The upper-platform ESO reconstructs feedback velocity and a bounded equivalent-displacement state, while the lower-platform ESO provides a smoothed velocity reference for feedforward compensation. The method was implemented on a plate-type active vibration isolation platform and evaluated using lower-to-upper-platform acceleration transmissibility over 0.1–10 Hz. Across three repeated 200 s records, the proposed ESO feedback–feedforward condition achieved an integrated input–output suppression ratio of $38.67\pm 0.46$ dB, reduced the upper-platform output acceleration RMS to $(1.31\pm 0.09)\times {10}^{-7}$ g, and provided a $48.92\pm 2.12$ dB RMS reduction relative to the passive baseline. Direct nominal–measured comparisons further showed that the reduced model captured the dominant passive and feedback-controlled dynamics. These results demonstrate that low-frequency active micro-vibration isolation can be achieved using only velocity measurements, without additional displacement sensors.