Research On Attitude Maneuvers Control Of Sgcmg Based Agile Small Satellite

The agile small satellite has rapid maneuver capability with at least an order of magnitude greater than conventional microsatellite, and this rapid maneuver capability is required for many military or commercial missions, for example, space surveillance, high-precision earth observation. In order to achieve a large angle rapid maneuvers of such small satellites, the Single Gimbal Control Moment Gyro (SGCMG) systems are the ideal candidate for the actuators of its'Attitude Control Systems (ACS) for the reasons of possessing the capability of torque amplification and lower power consumption. However, the difficulty of the mathematical modeling of ACS is increased for which the inertia matrix of the satellite is varied with the rotation of the gimbal of SGCMG, meanwhile, the inherent singular problem of SGCMG is particularly serious in the installation configuration such as pyramid. In order to make the actuator tracking the control input well, not only an effective SGCMG system steering law is needed to design to overcome its singularity problem, but also a high efficient attitude maneuver control law is required to design to overcome the problems such as excessive control input bought by the rapid maneuvers. All these problems are lucubrated in this thesis.(1) Attitude representation & kinematic equations of the satellite are summarized, and a more accurate but practical dynamic model of ACS as well as the SGCMG torque magnification formula are established, and the selection problem of the size of SGCMG is also studied. In this paper, the methods different from the existing literature are used in dealing with the of inertia matrix of SGCMG system with respect to its own center of mass which is part of the inertia matrix of the entire satellite. This part is not all of use or all of neglect, while the non-zero components and the cycle components with zero-mean are separated and treated respectively.(2) Aimed at singular problems of SGCMG system, the relationships between each singular parameter of system are established. the angular moment singular surfaces as well as the singular surfaces in gimbal configuration space are investigated, and the geometric characteristic expressions of the angular moment singular surfaces are also derived based on the ideas and methods of the algebra and differential geometry. Meanwhile, based on previous research, the bases of the subspaces in the gimbal angle tangent space at the singular states are fully derived,and Escapability at the singular state of system is also studied through the used of null space bases of the system's Jacobian matrix; Two necessary conditions of the Escapability are summarized. Many theoretical results are verified through an example of three SGCMGs with parallel gimbal axes.(3) The existing SGCMG system steering laws are briefly summarize and classified. The typical gimal angular rate steering laws are analyzed as well as the problems and their shortcomings. To overcome the gimbal"lock"phenomenon existed in those steering laws, an improved singular direction avoidance (SDA) steering law is proposed based on the singular value decomposition (SVD ) Theory, and its parameters tuning method is also investigated. Effectiveness of the new steering law is showed by some simulation results.(4) Trough the example of large angle re-orientation maneuver, the traditional quaternion feedback control law for maneuvers are studied, found some shortcomings that the peak of control torque command is too large,and convergence of the second half phase of the system is also slow and so on. To overcome those shortcomings, a new nonlinear backstepping control law is proposed based on the backstepping design method as well as the application of ideas such as variable gain control, and its parameters tuning method is also proposed aimed at the problem of too many parameters. The ACS closed-loop simulation results shows that the control law can be applied significantly inhibited the peak of control torque command, while ensuring the smooth of control law and stability of the system.