In the present study, a predefined-time attitude stabilization for liquid-filled spacecraft with large liquid sloshing is investigated under input saturation and external disturbance. First, the large slosh of the liquid is equivalent to the motion pulsating ball model (MPBM), and the dynamic model of the rigid-liquid coupling system is established. Then, liquid sloshing state quantity-related items and external disturbances are combined to form a lumped disturbance. A predefined-time disturbance observer is proposed to accurately reconstruct the lumped disturbance within a predefined-time regardless of the initial estimated state. Based on the proposed predefined-time disturbance observer, a predefined-time sliding mode surface is designed. The predefined-time stability of the proposed observer and controller is proved using the Lyapunov function. Finally, a variable-speed reaching law and exponential reaching law are combined to suppress the chattering caused by sliding mode control. To this end, a new auxiliary function is developed to consider the effects of input saturation. The simulation results show that the proposed controller can effectively stabilize the attitude stability of the liquid-filled spacecraft.
Focusing on cutting-edge scientific issues related to lunar exploration and applications, 9 overarching goals and 38 specific objectives for China's manned lunar exploration program have been proposed. Leveraging China's technical capabilities in manned spaceflight and lunar exploration, as well as its expertise in lunar and planetary science, the objectives center on scientific research, lunar-based scientific research, and resource exploration and utilization. Based on these scientific goals and trends in domestic and international manned lunar exploration landing site selection, China's basic principles and processes for selecting landing sites have been established. Thirty prime landing sites have been identified, including 11 low-latitude regions and 1 mid-latitude region, taking into account scientific value and engineering implementation conditions. These scientific objectives and landing site selection recommendations will serve as important guidance and top-level input for the design and implementation of China's manned lunar exploration program.
Aiming at the speed tracking control problem of micro-nano satellite momentum wheel with parameter uncertainties and external disturbances,a momentum wheel system dynamics model including model uncertainties and external disturbances is established.An adaptive neural network global fast terminal sliding mode control strategy is proposed.Firstly,a global fast terminal sliding mode control strategy is designed to accelerate the system response speed and achieve finite-time stability in the absence of external interference.Then,a radial basis function neural network is used to estimate and compensate for system parameter uncertainty and external disturbances.The neural network adaptive law is derived using Lyapunov method,and adaptive adjustment of the network weights is used to ensure system stability in the presence of disturbances.Finally,the simulation comparison shows that proposed control scheme not only has faster tracking,but also has better anti-interference ability and robustness.
On November 18,2023,SpaceX conducted the second orbital launch test of a Starship carrier rocket at its own launch site.The first stage of the rocket's upward flight was normal and successfully passed the MaxQ.The first and second stages of the rocket successfully completed thermal separation.Subsequently,multiple engines of the first stage malfunctioned during the flipping process,eventually exploding and disintegrating.The second stage experienced engine abnormalities after flying for several minutes,and the rocket ultimately triggered self destruction and failed to reach the predetermined orbit,resulting in a failed launch.Based on the relevant research content,the abnormal phenomena that occurred during the launch of the first and second stages of the rocket were sorted out,and the possible causes of abnormal phenomena and flight failures were analyzed.The experience and inspiration for similar rocket systems were summarized.
Aiming at the strong atmospheric drag torque and attitude control actuator failure of ultra-low-orbit satellite,a method to estimate and compensate the disturbance and fault is proposed based on the theory of concurrent learning strategy.Firstly,as an idea for parameter identification,the concurrent learning adaptive identification strategy is introduced into the problem of disturbances and faults estimation.Compared with traditional observers,the proposed strategy can estimate the disturbances and faults simultaneously and separately,and the attitude information and command torque are not required at all time.Then,based on the estimations,an attitude controller is designed to guarantee high precision of attitude control of the satellite with external disturbances and actuator faults.Finally,a set of numerical simulations of specific mission process is carried out to verify the effectiveness of the proposed method.
