In this paper, a simple and low-cost three-axis gimbal simulator is introduced. This simulator has been constructed in Amirkabir University of Technology and is used for implementation of attitude control algorithms of remote-sensing satellites in a real time condition using three reaction wheels as hardware in the loop test-bed. This simulator is modeled in Solidworks software package to determine its mass properties in order to utilize in obtaining the dynamic model of the simulator. Afterward, an attitude control algorithm is designed. Performance of the designed attitude control algorithm is investigated by implementing it on the simulator.
In impulsive orbital maneuvers, thrust vector misalignment from the center of mass is the serious source of disturbance torque. A high capacity attitude control system is needed to compensate the mentioned large exogenous disturbance. In this paper a new retrofiring control method is proposed and studied which is based on the combination of a 1DoF gimbaled thrust vector control and spin-stabilization method. Spin-axis stabilization and disturbance rejection are considered as two important attitude control objectives. The nonlinear two-body dynamics of a small spacecraft is derived in which dynamical interaction between the nozzle and the body is significant. Reaction control system is not used and the only active control part is a 1DoF gimbal. The spacecraft design efficiency is very important; therefore, the H∞ performance and control gain norm are chosen as two conflicting cost function in the Pareto front multiobjective optimization. Many Pareto fronts are given for some ranges of two favorable parameters: (1) spin rate and (2) spin-axis moment of inertia. Optimization variables are the closed-loop system poles. Moreover, poles region constraint is employed to obtain a well-damped transient response. From the perspective of performance and design efficiency, the optimization results give many attractive outcomes. The resulting system is an efficient design for a small spacecraft. Furthermore, numerical simulations are included to confirm the optimization results and illustrate the superiority of the proposed method compared to the only spin-stabilization.
We will design an extended interacting multiple models adaptive estimator (EIMMAE) for attitude determination of a stereoimagery satellite. This algorithm is based on interacting multiple models (IMM) extended kalman filters (EKF) using star sensor and gyroscope data. In this method, the motion of satellite during stereoimaging manoeuvres is partitioned into two different modes: "manoeuvring motion" mode and "uniform motion" mode. The proposed algorithm will select the suitable Kalman filter structure to estimate gyro errors accurately in order to maintain the peak attitude estimation error less enough at the beginning of manoeuvres while the satellite is in "manoeuvring motion" mode and then will select the suitable star sensor measurement noise level at the end of manoeuvres while the satellite is in "uniform motion" mode to reduce attitude estimation errors. It will be shown that using the proposed algorithm, the attitude estimation accuracy of stereoimagery satellite will be increased considerably. The effectiveness of the proposed algorithm will be examined and compared with the previous proposed methods through numerical simulations.
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