Dynamics And Control Of Space Inflatable Net Capture System

Facing the increasingly serious problem of space debris,countries around the world are developing space debris active cleaning technology vigorously.Space inflatable net capture system(SINCS)is an active cleaning system relying on inflatable beams to deploy nets for target capture,which has the advantages of stable structure,strong adaptability,large capture range and maneuverability.Therefore,it has a broader application prospect than the traditional tethered space net system,which has important military values and great economic benefits.In this paper,the system design and dynamic modeling of SINCS are carried out,and the dynamics and control problems of the key mission phases of the system,such as maneuver,capture,stabilization,are emphatically studied in order to provide theoretical and technical support for the space inflatable capture mission on orbit.SINCS contains large flexible inflatable deployed beams and nets,which make the system model has strong nonlinearity and uncertai nty.The dynamic characteristics of the system are difficult to predict because of the complex vibration and impact in the process of rapid maneuver and target acquisition.Firstly,the concept and task flow of SINCS are explained.Then,the equivalent beam dynamic model describing the bending characteristics of the inflatable beam is established by using the absolute nodal coordinate formulation(ANCF)and the failure theory of ideal thin film under pressure.Ignoring the cable torsion and shear deformation,an efficient ANCF cable central axis model is established.In addition,the dynamics of flexible body collision is studied based on Hertz theory.Finally,based on Lagrange dynamic equation,a differential-algebraic equation describing the geometric nonlinearity of SINCS can be established.Then,the dynamic analysis of SINCS are carried out.The research proves that the system has good stability under the influence of spatial microgravity environment and external excitation.In order to the problem of large deformation and vibration of inflatable beams and nets during rapid location maneuver,an optimal velocity maneuver strategy is proposed,which maintains the stability of the capture configuration of the system and ensures the maximum target encapsulation area.Aiming at the buckling failure of inflatable beams,tether closure and acquisition adaptability in the capture stage,a variable bending stiffness equivalent beam model and a driving constraint model of closure are established,which prove that the system has good acquisition adaptability to non-cooperative target position and relative angu lar velocity errors,and reduce the error requirement of measuring sensor.In the attitude maneuver phase of SINCS,the vibration of flexible inflatable capture mechanism is coupled with the service spacecraft,which makes it difficult for the system to achieve fast and accurate attitude maneuver control.In this paper,the quaternion-based attitude error dynamics equation is derived.An active disturbance rejection control(ADRC)based on error quaternion is designed to estimate and compensate the disturbance and uncertainty caused by deformations of inflatable beams and nets in real time,which effectively improves the attitude maneuvering accuracy of the system.Subsequently,aiming at the actuator saturation problem caused by the excessive amplitude of non-linear interference,an anti-saturation scheme based on error compensation is introduced to improve the anti-windup ability of the controller,which improves the maneuvering wrapping ability to the target.When SINCS catches large non-cooperative unstable targets,the structure and motion state of the system would change,resulting in an increase in the convergence time of the attitude stabili zation controller.A quaternion-based fixed-time non-singular fast terminal sliding mode control is proposed,which is independent of the initial state error and the upper bound of unknown disturbance.Fixed-time extended observer based on multivariable su perhelix is used to estimate the uncertainties and collisions of the combined system.The fixed-time non-singular sliding mode control law is deduced and proved,which realizes the fast,low-energy and stable attitude control of the combined system after capture,and greatly improves the security of the capture.In order to solve the problem of continuous saturation of the controller caused by excessive disturbance,a hybrid sliding mode control and ADRC based on fixed-time observer is proposed,which effectively reduces the impact of saturation and collision.