This article investigates a distributed game strategy for formation control of multispacecraft subjected to nonlinear dynamics and J ₂ perturbations. In the proposed problem, each spacecraft is devoted to minimize its own performance cost using only local information, whereas the overall formation system attempts to seek an optimized decision based on communication topology. Therefore, in our scheme, the formation control problem can be treated using a Nash strategy. A worst case Nash strategy is proposed against the disturbance defined as a player, and we prove rigorously that an open-loop Nash equilibrium exists in the underlying problem. Then, a distributed terminal state observer is introduced to facilitate the local implementation of the proposed Nash strategy. Simulation results verified the performance of the proposed scheme.

Estimation of the time-difference-of-arrival (TDOA) between a signal and its time-shifted version has many applications, mostly in localization. Because compressive sensing (CS) can reduce the sampling rate and data volume, TDOA estimation from CS samples (CS-TDOA) has become a subject of interest. Generally, CS-TDOA has lower estimation accuracy and the Cramer-Rao bound (CRB) can quantify this degradation. The first part of this correspondence derives the CRB for CSTDOA estimation. In the second part, it proposes an incoherent processing scheme for CS-TDOA estimation using partial Fourier coefficients. It has the advantage of reducing the number of sampling channels needed to acquire those coefficients. Simulation results are given to corroborate the theoretical development.

This correspondence investigates the under-actuated spacecraft attitude maneuver problem using two parallel single gimbal control moment gyros (SGCMGs). According to the configuration of the SGCMGs, the principle axes of the spacecraft are divided into two parts: namely the axes with and without direct control input. Based on this division, a two-level control strategy: a low level tracking control part to track the desired angular velocity error about the axes with direct control input and a high level sliding mode control part to stabilize the angular velocity error, is developed. Four numerical scenarios are conducted to verify the proposed control logic. Simulation results show that the target attitude is a global equilibrium, and any attitude can be reached when the whole system is feasible. If the controllability is not satisfied, the spacecraft rotates in the adjacent region around the desired attitude.

As a part of China’s Chang’e-4 lunar far side mission, two lunar microsatellites for low frequency radio astronomy, amateur radio and education, Longjiang-1 and Longjiang-2, were launched as secondary payloads on 20 May 2018 together with the Queqiao L2 relay satellite. On 25 May 2018, Longjiang-2 successfully inserted itself into a lunar elliptical orbit of 357 km × 13,704 km, and became the smallest spacecraft which entered lunar orbit with its own propulsion system. The satellite carried the first amateur radio communication system operating in lunar orbit, which is a VHF/UHF software defined radio (SDR) designed for operation with small ground stations. This article describes and evaluates the design of the VHF/UHF radio and the waveforms used. Flight results of the VHF/UHF radio are also presented, including operation of the radio, performance analysis of downlink signals and the first lunar orbit UHF very-long-baseline interferometry (VLBI) experiment.