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This paper focuses on the attitude pointing control problem under pointing-forbidden constraints and performance constraints. The spacecraft is expected to align its sensor's boresight to a desired direction, while the terminal control accuracy and the attitude adjustment rapidity should also be guaranteed simultaneously. To resolve this problem, a switching controller structure is proposed in this paper based on the reduced-attitude representation, fusing the artificial potential field (APF) methodology and the Prescribed Performance Control (PPC) scheme together. Firstly, a novel artificial potential field is presented, and a particular function is designed for the mollification of the switching process, aiming at providing a smooth transition for the system status. Subsequently, we propose a special performance function, which can freeze the PPC part when necessary. In this way, the intrinsic contradictory between the fast attitude maneuver and forbidden direction avoidance is tackled Further, an asynchronous switching strategy is designed, guarantees the system's stability. Based on these proposed issues, a switching backstepping controller is developed, and a tracking differentiator(TD) is employed to generate a smooth approximation of differential signals. Numerical simulation results are illustrated to show the effectiveness of the proposed scheme., Comment: 12pages, 15 figures

This paper considers the prescribed performance control (PPC) of spacecraft attitude tracking under multiple physical constraints, focusing on the robust issues. A novel Barrier Lyapunov function is proposed to realize the guaranteed-performance control under angular velocity constraint without singularity. Additionally, an adaptive strategy for the performance function is presented to soften the constraint and quickly re-stabilize the system after severe disturbances occur, providing strong robustness. Further, an auxiliary system is designed to handle the input saturation issue, incorporating the actuator limitation into the system. Based on the proposed structure, a backstepping controller is developed accordingly using a double-layer PPC framework. Numerical simulation results are presented to validate the proposed controller framework's efficiency and robustness.8 pa, Comment: 8 pages, 11 figures

The attitude tracking problem with preassigned performance requirements has earned tremendous interest in recent years, and the Prescribed Performance Control (PPC) scheme is often adopted to tackle this problem. Nevertheless, traditional PPC schemes have inherent problems, which the solution still lacks, such as the singularity problem when the state constraint is violated and the potential over-control problem when the state trajectory approaches the constraint boundary. This paper proposes a Singularity-Avoidance Prescribed Performance Control scheme (SAPPC) to deal with these problems. A novel shear mapping-based error transformation is proposed to provide a globally non-singular error transformation procedure, while a time-varying constraint boundary is employed to exert appropriate constraint strength at different control stages, alleviating the potential instability caused by the over-control problem. Besides, a novel piece-wise reference performance function (RPF) is constructed to provide a relevant reference trajectory for the state responding signals, allowing precise control of the system's responding behavior. Based on the proposed SAPPC scheme, a backstepping controller is developed, with the predefined-time stability technique and the dynamic surface control technique employed to enhance the controller's robustness and performance. Finally, theoretical analysis and numerical simulation results are presented to validate the proposed control scheme's effectiveness and robustness., Comment: 18 pages,18 figures

Almost all existing studies on inter-satellite radio-frequency (RF) measurement have focused on two-satellite formations. Although some frequency division multiple access and code division multiple access multisatellite RF measurement schemes have been proposed, their poor scalability does not satisfy the inter-satellite measurement requirements of multisatellite formations, especially large-scale formations. Two-way ranging (TWR), which is based on a time division mechanism, is an effective solution that has been used for inter-satellite links in the global positioning system and Beidou navigation constellations. However, the high measurement accuracy achieved with TWR in these navigation constellations is heavily reliant on high-performance atomic clocks and the assistance of navigation ephemeris, which are not available on microsatellite platforms. This work focuses on a scalable multisatellite measurement scheme that adopts a distributed broadcast-based time division multiple access mechanism as the media access control layer and uses an asymmetric double-side TWR method as the physical layer. The measurement performance of the proposed scheme is evaluated through in-depth theoretical modeling, simulation verification, and experimental validation, along with a comprehensive comparison with the conventional TWR method. The experimental results show that centimeter-level measurement accuracy can be achieved with the proposed scheme when only a common miniaturized frequency source is used. This accuracy level is two orders of magnitude better than that of the TWR method, and thus satisfies the application requirements of general large-scale microsatellite formations.

This paper proposes two methods to mitigate the zero bias of noncommensurate sampling based code-tracking loops to significantly improve the pseudonoise ranging accuracy. For the compensation-based method, a set of algorithms is developed to directly calculate the zero bias which is then removed from the range measurement. For the compensation-free method, a special category of sampling ratios are selected such that the zero bias is self-cancelled. Simulations validate the effectiveness of the proposed methods.

In this article, a direct and key factor which affects separation parameters of satellite-rocket separation mechanism called optimization method of minimizing external moment is introduced. By changing the positions of elastic launch devices, popping process is effectively controlled. This optimization method is proved by ground test which can offset gravity, and it particularly adapts to the fixed and non-stable status elastic parameters, the distribution of all kinds of elastic devices and bias aircrafts which are hard to make the correction. The method has successfully applied to prediction and optimization for the separation of “Zhejiang University BJ Pico-satellite”. It is widely used now in practice with its easy operation.

Gold codes are widely used for pseudo-noise (PN) ranging, and non-commensurate sampling is an effective solution to improving the tracking performance of digital code tracking loops. However, the sequence transition density of gold codes is low, which limits the achievable ranging accuracy. Here, the authors present a non-commensurate sampling and double-loop-based regenerative PN code tracking approach. With this approach, the tracking of the original regenerative code is equivalent to that of its clock component, and the sequence transition density is maximised. Thus, the tracking error is apparently reduced and optimal tracking performance is achieved. In the double-loop structure, a unified tracking loop is employed to facilitate performance comparison. Simulation results demonstrate the performance improvement of the proposed approach over the traditional gold code tracking scheme, and the relationship between the non-commensurate sampling parameters and the achievable tracking accuracy. The approach is especially suitable for precision ranging applications, and can be extended to other applications involving accurate signal tracking in digital equipment.

In this paper, a TGV interposer based wafer level packaging for inertial MEMS devices is presented. For the TGV interposer, there is a redistribution layer of Al wiring on each side, which are electrically connected with Al metalized TGV. Being as a capping wafer, it's bonded to a MEMS accelerometer wafer based on bulk silicon process with a patterned benzocyclobutene(BCB) layer to achieve wafer level package. To verify the process, TGV interposer is fabricated and experiment results prove that Al TGV interconnection is electrically conductive. TGV interposer capped MEMS accelerometer is demonstrated and the tested shear bonding strength is about 69.84N with two concentric rectangular rings made of BCB adhesives, where the inner ring is about 6300µm × 5000µm with a width of 200µm and the outer ring is about 680µm × 5500µm with a width of 150µm.

Noncommensurate sampling is an effective solution for improving the tracking performance of digital code tracking loops. So far there has been a lack of a generalised method for designing the parameters of this sampling scenario. A simple approach to choosing the parameters of noncommensurate sampling is presented, which is based on the analysis of the quantitative relationship among the chip phase delay discrimination, the sampling ratio and the correlation length. Numerical and simulation results show that optimal phase delay discrimination and thereby superior tracking accuracy can be achieved with the proposed approach. This approach is especially suitable for precision ranging applications, and can be extended to other applications involving accurate signal tracking in digital equipment.