Dynamics And Control Of Space Net Deployment And Combination Reorbiting

Active debris removal, especially the defunct satellites mitigation in the GEostationary orbit(GEO), has become a hot issue in the space field. The net capture and combination reorbiting has provided a new and effective means for the space debris disposal and counterspace operations, indicating an extremely wide application prospect and great development potential. Aiming at the removal of the GEO defunct satellites, divided by two work modes of non-spinning and spinning, this dissertation focuses on the nonlinear dynamics and deployment control of the flexible net, and the dynamic characteristics and reorbiting control of the tether combination after capture.(1) Dynamics of the space non-spinning net system. Considering different mechanical environment in space and on ground, a lumped-mass model of space net is established, and the reliability of the simulation model is verified by the ground test. During the deployment process of the space net, the deployment area first increases and then decreases, while the total mechanical energy of the system is always on the decline. The magnitude of elastic potential energy of the system is very small, and the tether segments experience the state alternative between tension and slack all the time. The orbital altitude and capture direction have no influence on the deployment area and flight distance, but bring on different lateral offset. However, thanks to the redundant design of the net size, the net capture is still effective.(2) Deployment parameter analysis and optimization design of the space non-spinning net system. Based on the orthogonal experimental method, the sensitivity analysis of the space non-spinning net system is carried out, by which the primary and secondary order and significant degree of the design parameters are determined. The design parameters of low sensitivity is discarded to include only the casting velocity and casting angle, and the performance indices are condensed to the time of maximum deployment and the distance of maximum deployment. The surrogate models of the space non-spinning net system are established with the QPRS(Quadratic Polynomial Response Surface) method and Kriging method, and the latter is chosen through the accuracy assessment. Based on the Kriging surrogate model, the multi-objective optimization problem of the net deployment performance is solved using NSGA-II(Non-dominated Sorting Genetic Algorithm II) algorithm, and several Pareto solution is obtained.(3) Dynamics and control of the space spinning net system. The deployment process of the space spinning net system can be divided into two phases of arm deployment and net deployment. The system dynamics model is established according to different characteristics of the two phases, and the correctness of the dynamic model is verified by the conservation law of the kinetic energy and angular momentum during the uncontrolled deployment of the spinning net. Several torque control strategies are compared through simulation, and the MK(Melnikov-Koshelev) control law is adopted since it can avoid the net coiling off and save energy consumption. From the simulation of the spinning net deployment process under MK control, we find that under the effect of the centrifugal force and the damping effect, the spinning net can eventually get to a stable configuration, and may undergo strong in-plane disturbances after going stable. In order to eliminate the capture error arising from the spinning net’s long time on-orbit flight, the casting angle should be slightly modified to counteract the influence of the orbital dynamics.(4) Reorbiting dynamic analysis of the tether combination. On the assumption that the tug and target are considered as rigid bodies and the net as four flexible bridles, a four-bridle and double-rigid-body model for the tether combination is established, and the system dynamics equations are developed taking into account the system orbital motion, relative motion of two spacecraft, spacecraft attitude motion and quality change of the tug. The particle method and equilibrium point method are tested in the tension calculation of the tether and bridles, and the equilibrium point method is chosen for its high computational efficiency. The system stability in various initial states is examined on the premise that no active control but only a constant circumferential thrust is applied. The simulation results indicate that the system is disturbed greatly if the initial state deviates from the reference state. When the system is initially in a reference state, the influence rule of different magnitude of the thrust on fuel consumption and reorbiting time is analyzed, and the simulation results indicate the existence of an optimum value of the thrust.(5) Reorbiting control of the tether combination. The reorbiting control of the tether combination is composed of de-spinning, orientation and tugging, which have all been investigated in the control law design and simulation based on the PD feedback control and LQR(Linear Quadratic Regulator) control method. To decrease the target’s rotation, the direction of the tether tension must be kept in the target’s rotation plane, and the active control of the tether tension must be applied to decrease the angular velocity of the target. To orient the tether combination, firstly an expected turnaround trajectory has been planned, and then the tracking control is applied. The tugging control of the tether combination is designed not only to transfer the system to the graveyard orbit, but also to keep the system stable in the tugging process. The validity of these control laws are proved by the simulation results, and a safe transfer of the system to the graveyard orbit has been achieved.To sum up, a study on dynamics and control is carried out on three research objects of space non-spinning net system, space spinning net system and tether combination, which are extracted from the mission of net capture and combination reorbiting. These studies build an analysis framework for the mission of net capture and combination reorbiting, and provide an important method, model and analysis results for further theoretical study, ground test and on-orbit test.