Research On Attitude Control System Key Technologies For Micro-Satellite

Micro-satellite is becoming an important direction of spacecraft development due to the advantages such as low cost, high density of functionality and short research developement cycle. The ACS is the most important subsystem that partly defines the function of satellite. Bacause the ACS micro-satellite is under stringent constraints on mass, volume and power, so the purpose of this paper is to design a high performance ACS that satisfied with system constraints and mission demands. Taking the"TXZ"micro-satellite that developing by NUAA an example, the relevant theories, methods and key technologies are studied systematically in this dissertation, and the main content and achievements are as follows:1. Based on the analysis of mission for"TXZ"micro-satellite and its requirements towards ACS, a feasible scheme of the ACS configuration as well as the performance of the sensitive and executive organs are outlined.The integrated mathematical model about ACS for micro-satellite is established, including model of kinematics, dynamic, sensor, actuator and disturbance. The influence of disturbance torque for the attitude control is simulated and analysised, in addition the stabilization of satellite is studied using an energy consideration method.2. A new combined filter for attitude determination is presented which syncretize the two vectors method with EKF or UKF. It reduces high dimension vectors to quaternion, so the nonlinear observation equation is turned into linear that reduce the computational requirement and enhance precision. Using magnetic sensor, sun sensor and gyro, nine filters namely EKF incorporating gyro, EKF or UKF without gyro are developed, that based on direct observation or deal with by q-method and Gauss-Newton method in advance. The simulation result illustrates that indirect method have better effect especially by Gauss-Newton algorithm.3. Aim to the pivotal phase of initial attitude control, the detumbling and the large attitude acquisition controllers using assimilated PD control as well as limited attitude feedback using micro-thrustors are designed. On the other hand the B-dot, energy, sliding mode and limited attitude feedback controllers using magnetic torque are designed. A new method for B-dot detumble and attitude acquisition with the wheel circumgyrate synchronously, as wheel as the initial control scheme using Y-Thomson are proposed. For all the thruster and magnetic contol method, the detailed theoretic and simulating analysis is conducted.4. For normal task phase the pitch axis controller using a momentum wheel and momentum unloading using magnetic torque are developed. A new magnetic controller for nutation and precession damping is given, and its parameters are investigated by MTS method that given preferable instruction for practical application. Moreover with constant wheel the active magnetic controllers are designed for three-axis stabilization, which avoid the momentum satuation and make control process convenient.5. The combined control methods using thrusters plus a momentum wheel are researched. Firstly the LQG and lyapunov control law are designed for stabilization, then three nonlinear controllers of lyapunov, sliding mode and feedback linearization control are designed for large angle maneuver which not only have high precision but alse account for real-time need. The attitude control of underactuated satellite with thruster failure is studied using a new method named (w,z) parametrization. The attitude stabilization and reorientation controllers under actuator failure are designed and validated by simulation tests.6. Based on VxWorks operating system the ACS software designing is carried out. The design philosophy using micro kernel and hierarchical structure method for software system is given. Meanwhile the system schedule of several-tasks, the managing control mode and communication among tasks in every mode are completed for ACS. The simulations indicate that it has the high reliability and extensibility, thereby, can be supported for further develop of micro-satellite.In a word, the ACS for mission demands of"TXZ"satellite is studied deeply and its key technologies are resolved effectivly in this thesis. There are many innovations with great applied value in theory and method which can give reference and instruction in developing the high performance ACS for other micro-satellite.