For a drag-free satellite, one core technology required to achieve the mission requirements is drag-free control. The purpose of control is to offset the interference such as sunlight pressure, gravitational gradients of Earth and Moon, nonspherical perturbation, etc. Currently, the drag-free controller design is mainly aimed at the full frequency band. This will inevitably mix the control signal into the scientific measurement signal, thereby interfering with the processing of scientific data. Besides, the control at the full frequency band will increase fuel consumption. To solve the above problems, this article presented the controller design method for a drag-free satellite with scientific measurement constraints, which covers motion model establishing, coordinate axis decomposition, frequency separation control strategy formulation, H∞ mixed sensitivity controller design, controller stability analysis, and performance results.

With the development of deep learning and super-resolution reconstruction, the performance of single-image super-resolution (SISR) has improved significantly. However, most of them cannot strike a great balance between computational cost and performance, which prevents them from being deployed on edge devices. Additionally, feature fusion and channel mixing are not considered in most lightweight networks, leading to the limited performance of these networks. To solve such problems, we propose a lightweight pyramid feature fusion network (PFFN), which mainly contains the pyramid spatial-adaptive feature extraction module (PSAFEM) and the enhanced channel fusion module (ECFM). They can extract global-to-local feature, build long-range dependence with small parameters increment and realize channel and spatial feature fusion. Finally, some state-of-the-art methods are utilized to compare with our network. Extensive experimental results indicate that our PFFN outperforms these methods in parameters, flops and performance.

Purpose: The purpose of this paper is to resolve complex nonlinear dynamical problems of the pitching axis of solar sail in body coordinate system compared with inertial coordinate system. And saturation condition of controlled torque of vane in the orbit with big eccentricity ration, uncertainty and external disturbance under complex space background are considered. Design/methodology/approach: The pitch dynamics of the sailcraft in the prescribed elliptic earth orbits is established considering the torques by the control vanes, gravity gradient and offset between the center-of-mass (cm) and center-of-pressure (cp). The maximal torques afforded by the control vanes are numerically determined for the sailcraft at any position with any pitch angle, which will be used as the restriction of the attitude control torques. The finite/infinite time adaptive sliding mode saturation controller and Bang–Bang–Radial Basis Function (RBF) controller are designed for the sailcraft with restricted attitude control torques. The model uncertainty and the input error (the error between real input and ideal control law input) are solved using the RBF network. Findings: The finite true anomaly adaptive sliding mode saturation controller performed better than the other two controllers by comparing the numerical results in the paper. The control torque saturation, the model uncertainty and the external disturbance were also effectively solved using the infinite and finite time adaptive sliding mode saturation controllers by analyzing the numerical simulations. The stabilization of the pitch motion was accomplished within half orbit period. Practical implications: The complex accurate dynamics can be approximated using the RBF network. The controllers can be applied to stabilization of spacecraft attitude dynamics with uncertainties in complex space environment. Originality/value: Advanced control method is used in this paper; saturation of controlled torque of vane is resolved when the orbit with big eccentricity ration is considered and uncertainty and external disturbance under complex space background are settled. Moreover, complex and accurate nonlinear dynamical model of pitching axis of solar sail in body coordinate system compared with inertial coordinate system is provided.

The establishment of a laser link between satellites, i.e., the acquisition phase, is a key technology for space-based gravitational detection missions, and it becomes extremely complicated when the long distance between satellites, the inherent limits of the sensor accuracy, the narrow laser beam divergence and the complex space environment are considered. In this paper, we investigate the laser acquisition problem of a new type of satellite equipped with two two-degree-of-freedom telescopes. A predefined-time controller law for the acquisition phase is proposed. Finally, a numerical simulation was conducted to demonstrate the effectiveness of the proposed controller. The results showed that the new strategy has a higher efficiency and the control performance can meet the requirements of the gravitational detection mission.

This study proposes a three-spacecraft formation reconfiguration strategy of minimum fuel for space gravitational wave detection missions in the high Earth orbit (10⁵ km). For solving the limitations of measurement and communication in long baseline formations, a control strategy of a virtual formation is applied. The virtual reference spacecraft provides a desired relative state between the satellites, which is then used to control the motion of the physical spacecraft to maintain the desired formation. A linear dynamics model based on relative orbit elements’ parameterization is used to describe the relative motion in the virtual formation, which facilitates the inclusion of J₂, SRP, and lunisolar third-body gravity effects and provides a direct insight into the relative motion geometry. Considering the actual flight scenarios of gravitational wave formations, a formation reconfiguration strategy based on continuous low thrust is investigated to achieve the desired state at a given time while minimizing interference to the satellite platform. The reconfiguration problem is considered a constrained nonlinear programming problem, and an improved particle swarm algorithm is developed to solve this problem. Finally, the simulation results demonstrate the performance of the proposed method in improving the maneuver sequence distribution and optimizing maneuver consumption.