The separation and reconfiguration of stacked satellites in orbit is an effective technique for constructing large space structures. The natural coordinates formulation is used to establish the dynamic equations for stacked satellite systems, which has the advantage of facilitating the handling of fixed constraints between satellites. Suitable strategies for autonomous assembly separation and assembly are devised. A spin separation method is employed to achieve collision-free separation of satellites, while PD control and the potential function is utilized for satellite assembly. Additionally, an optimization algorithm is employed to calculate the minimum distance between satellites, enabling precise determination of the potential function's magnitude. By implementing these methods in simulations, the complete process from separation of stacked satellites to segmented assembly is realized, which confirming the effectiveness of the proposed separation and assembly strategies.
To validate the influence of the stress wave propagation on the arresting process,this paper presents a study of the proportion-integral-differential(PID) control of the arresting process during carrier aircraft landing with consideration of the kink-wave that travels along the arresting cable.Taking the hydraulic damping force as a control input for the arresting process,a dynamic model for an ideal arrestment without the kink-wave is first established.Based on the constant hook load condition during the arresting process,a set of ideal trajectories is obtained with an optimal control method.Afterwards,the propagation characteristics of the kink-wave that travels between the deck sheave and the hook are analyzed.Then a discrete kink-wave model is obtained and applied to the PID control of the arresting process in tracking an ideal trajectory.The result shows that when the kink-wave is taken into consideration,the hook load will vibrate at the initial period of the arresting process,which is consistent with the experimental result of American military standard MIL-STD-2066.
The paper focuses on the separation and deployment dynamics of an on-orbit compactly connected multi-rigid-body (MRB) system, which could separate autonomously from a carrier spacecraft. Based on the focused MRB system, it is not necessary to repeatedly use the launcher of the carrier spacecraft or install multiple launchers in the spacecraft to separate the MRB system. This is advantageous because it can effectively improve the space utilization rate of the spacecraft, simplify the separation deployment operations and reduce the risk of collision between rigid bodies. To realize the separation of such a MRB system, the paper presents an investigation on its on-orbit dynamics and the design of collision-free separation deployment schemes. Firstly, a dynamic model of a single rigid body is established based on the principle of virtual work and the Natural Coordinate Formulation (NCF) method accounting for the relative motion between rigid bodies and attitude changes of each rigid body. Considering the orbital motion, the variations of connecting constraints of the MRB system and the interactions between rigid bodies during the separation, the governing nonlinear dynamic equations including constraints of the system are obtained with a method of Lagrange multipliers. With practical engineering applications taken into consideration, the separation deployment of MRB system is realized through ejection mechanisms mounted on the four corners of each contact surface between rigid bodies. Secondly, the timing sequences of separation maneuvers are specially programmed and two separation schemes are developed by adjusting different ejection directions and ejection sequences to guarantee the non-collision between rigid bodies in the separation deployment. Finally, numerical case studies are presented for investigating the nonlinear dynamic behaviors of rigid bodies and demonstrating the effectiveness of separation schemes.
The space industry in China is eager to have the advanced technology of large space structures composed of trusses cables and meshes. Such a large space structure, deployed on orbit, may serve as the large antenna for different space missions. The important scientific basis of the technology is the nonlinear dynamics modeling, analysis and control of these space structures during their deployment and service. This review article surveys the advances in relevant researches and proposes three open problems as follows. The first is the flexible multibody dynamics for the deployment of such a space structure, especially the nonlinear dynamics modeling and analysis for the contacts and wraps of mesh under microgravity, the internal impacts in clearance joints, and the coupling between structure deployment and spacecraft attitude. The second is the dynamics analysis of the space structures after deployment and during service, especially the complicated nonlinear vibrations of the flexible structure with numerous backlash joints under periodic thermal impacts. The third is the dynamic control of the space structures after deployment and during service, especially the under-actuated and lower-powered control for structure vibrations and waves.
In this paper,the lumped mass finite element is proposed to describe the one-dimensional continuum during deployment/retrieval.The discrete dynamic model that is capable of describing the time-varying multi-degrees-of-freedom system is presented.Because of the time-varying properties,the local elements of the system need to be redivided when the number of degrees of freedom of the system changes,and accordingly the lumped mass,damping and stiffness matrices as well as the displacements and force vectors are to be updated at every step computation.A configuration computation scheme is developed for solving the time-varying dynamic systems,which is based on an improved finite difference method.A tethered-like pendulum is selected as case studies here to verify the effectiveness of the proposed computational method.
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