Attitude Takeover Control In Post-capture Of Target By Space Robot

With the development of space technology, the launching of satellites has been increasing in number, while the number of on-orbit failures also increases remarkably. When the spacecraft reaches the end of life, in most cases its payload will still be able to work. Because of fuel exhaustion or actuator fault, the ability of three-axis attitude and orbit control will lose. However, if the ability of attitude and orbit control can be recovered, the satellite will be able to continue to work. The technology of spacecraft takeover control to extend the operational lifetime of spacecraft in orbit provides a new idea for these failed satellites. The service spacecraft will take over attitude and orbit control functions with a surrogate control system for the target spacecraft, allowing the target to continue to operate the other functions on the satellite as normal. For the on-orbit servicing of the non-cooperative target spacecraft which is not designed with custom grappling mechanical interfaces or visual marker, the space manipulator capture using visual servoing is one of the most promising ways to overcome the technical challenge. Therefore, one particular scenario for spacecraft takeover control mission is to use the space manipulator mounted on the service spacecraft to capture the liquid apogee engine nozzle or launch vehicle interface ring of target spacecraft. Therefore, in the background of SUMO/FREND project, we study the technology of spacecraft attitude takeover control in post-capture of target by space manipulator, which can provide the theoretical support in on-orbit services, such as satellite life extension, stranded satellite rescue, debris removal, and so on.Due to the unknown mass properties of the non-cooperative target spacecraft, the uncertain or unknown parameters are a big challenge for attitude takeover control. The combined spacecraft system in post-capture of target by space manipulator will be a highly nonlinear time-varying system with parameter changes and strong coupling dynamics. Currently, the study of the spacecraft attitude takeover control in post-capture of target by space manipulator is exceptionally rare, and the theoretical researches and the validation experiments are rather lacking, and there are many key scientific issues unresolved. Thesis for the spacecraft attitude takeover control in post-capture of target by space manipulator will study the scientific issues involved in the mass properties parameter identification, the control system reconfiguration and the actuator control reallocation, and other aspects. The main contents and research results are as follows:Firstly, for the mass properties parameter identification of the non-cooperative target spacecraft captured by space manipulator, the parameter identification method of the mass properties of the non-cooperative target spacecraft based on the space manipulator motion is proposed. The identification method utilizes a wide range of motion of space manipulator to change the weight distribution of the combination of spacecraft systems, and change the combined spacecraft velocity,and then solves the recursive least squares solution by the momentum conservation of the combined spacecraft to identify inertia properties of the non-cooperative target spacecraft. This identification method requires only a wide range of motion of space manipulator, and does not consume valuable jet fuel, and also decouples the parameters of the mass, the center of mass and the inertia. Moreover, the identification method only requires the velocities of the spacecraft to be measured, rather than acceleration and force, and has high identification accuracy.Secondly, for the attitude stability takeover control of target spacecraft that has the control system failures as well as a combination of the exact model, the method of the attitude stability takeover control of target spacecraft based the reaction wheels control system reconfiguration is proposed. The method uses the SDRE(Sate-Dependent Riccati Equation) control methods based-? stability design to reconstruct the service spacecraft attitude control law, and get the suboptimal control law of SDRE controller by the ?- D solving method, and then, it adopts the pseudo-inverse control allocation algorithm to reallocate the desired torques generated by the attitude control reconfiguration law among the reaction wheels. This method enables the closed-loop poles of the system away from the imaginary axis, which has better stability and higher real-time performance. However, due to the limited control torque and saturation of reaction wheel, considering the coupling torque generated by the wide range of motion of space manipulator is large and can be used as attitude control torque of the combined spacecraft. Therefore, for the large attitude error case, an attitude stability takeover control approach for target spacecraft is proposed based on the estimated coupling torque of manipulator. The method adopts the CPSO(Chaotic Particle Swarm Optimization) algorithm to plan motion trajectory of space manipulator, and then designs the reconfigurable sliding mode control law based on the estimated coupling torque of manipulator with assistance of the reaction wheels, in order to achieve the attitude stability takeover control of target spacecraft. This method makes use of the coupling torque of space manipulator, and overcomes the shortcomings of the limited control torque and saturation of reaction wheel, without consuming expensive jet fuel.Furthermore, for the attitude maneuver takeover control of target spacecraft that has the control system failures as well as a combination of the unkonwn model, the method of the attitude maneuver takeover control of target spacecraft based the thrusters control system reconfiguration is proposed. This method separates the unknown inertia parameter of combined spacecraft systems from Lagrange dynamics equation by the linear method, and then, it adopts the null-space pseudo-inverse control allocation algorithm to reallocate the desired torques generated by the reconfigurable attitude control law among the thrusters, to achieve the attitude maneuver takeover control of target spacecraft that has the control system failures as well as a combination of the unkonw model. This method not only ensures the tracking errors of position and velocity global convergence, but also considers the thrusters saturation constraint, and meets the real-time requirements of spacecraft.Finally, for the attitude maneuver takeover control of target spacecraft that has the part of actuator failures as well as a combination of the uncertain model, the method of the attitude maneuver takeover control of target spacecraft based redundant thruster dynamic control allocation is proposed. The method uses commond filter backstepping control to design reconfigurable attitude control law, and analysis system stability by Lyapunov method, and then, it utilizes the dynamic control allocation algorithm based on the constrained quadratic programming to reallocate the desired torques generated by the attitude control law among the thrusters of service spacecraft and target spacecraft. Last, considering the fuel consumption, it is compared with the method that only the thrusters of service spacecraft are used. The method can implement the position and speed constraints of the actuator, and achieves attitude maneuver takeover control of target spacecraft which has the part of actuator failures as well as a combination of the uncertain model, and avoids the spacecraft affected by the plume impact. In particular configuration of the redundant thruster, the method can take advantage of the thrusters of the service spacecraft and target spacecraft, and consume less fuel, compared with the method that only the thrusters of service spacecraft are used.