Research On Micro-Satellite Attitude Determination Scheme And Algorithm Based On Star And Earth Vector Observation

Modern micro-satellites are attracting more and more attention all over the world because of the low-cost, smart characters and ability of testing new technologies. In this dissertation, three-axis stable micro-satellite being the object, the attitude determination technology is researched. The main work is as follows:At first, for two different types of micro-satellites, two schemes are put forward: (1) attitude determination system composed of gyros and star sensor which can be used on micro-satellite which has larger mass and requirement of high attitude precision; (2)attitude determination system composed of three-axis magnetometer and earth-sensor which can be used on micro-satellite which has lower mass and requirement of lower cost. Next, algorithms for these two schemes are researched. In scheme(1), algorithm based on Extended Kalman Filter(EKF) and quaternion is researched. In scheme(2), two algorithms are researched, one is based on EKF and quaternion, the other is based on EKF and Modified Rodrigues parameters.To improve the attitude precision in scheme(1), further research is performed. First, the method to resolve the problem that star sensor'measurement has delay is presented. Second, by analyzing the gyro's error on satellite, a calibrating model is established and an algorithm based on EKF is researched, this algorithm can calibrate gyros accurately by some maneuver and can provide higher attitude precision. At last, simulation is carried out to verify the validity of the two algorithms.To improve the attitude precision in scheme(2) , advanced nonlinear filters are introduced into system. First, by reason that the Unscented Kalman Filter (UKF) has more superiority than EKF when used in nonlinear system, the attitude determination algorithm based on UKF is researched. Second, to enhance attitude accuracy when noise is non-gaussian, attitude determination algorithm based on Particle Filter(PF) is researched. Last, simulation is carried out to verify the superiority of the two algorithms.At last, using PC104 and VxWorks, the algorithm based on gyros and star sensor is implemented, at the same time, the simulation system is established to verify the implemented algorithm's validity.