Investigation and development of nontraditional approach for attitude estimation of small satellites

IGRF (International Geomagnetic Reference Field) and Tsyganenko's T89 magnetic field models are the selected models for the comparative study. These models can be one of the input vector separately besides the Sun direction to Singular Value Decomposition (SVD) method. Extraterrestrial effects coming from the Sun and/or interplanetary rays are the main consideration for estimating the magnetic field components close to the actual results. T89 model that uses an index changing with the external effects needs a model (IGRF) simulating the terrestrial magnetic field changes. Proposed models give the results in an acceptable limit with respect to the measurement data. Moreover, T89 model is the best-fit model if the absolute errors for the attitude angles are calculated. The difference between the defined models can be ignored with decreasing altitude but also become important on the higher orbits. This research also describes the development of nontraditional attitude determination system that can rely on sensor measurements which are magnetometer, sun sensor and rate gyros. Vectors coming from the selected sensor data and developed models can be placed in Wahba's problem. The system uses SVD method to minimize the Wahba's loss function and determine the attitude of the satellite. In order to obtain the attitude of the satellite with desired accuracy an extended Kalman filter (EKF) for satellite's angular motion parameter estimation is designed. The SVD and EKF algorithms are integrated for estimation of the attitude angles and angular velocities. The nontraditional method is compared with the traditional approach which uses the same sensors as magnetometer and sun sensor in addition to the gyros. In the eclipse period, algorithm is switched into the prediction phase for better attitude estimation of the satellite; therefore, satellite's attitude angles when no data coming from the sun sensor are improved. Magnetometers are assumed to be calibrated before the nontraditional technique is applied on the satellite. All the necessary algorithms are designed in the MATLAB package program and the simulations are performed using that software. The test platform has been used for the verification of the algorithms presented. The algorithms are implemented on the test platform using the magnetic field sensor data in the single-frame method.