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Development and Comparison of Estimation Methods for Attitude Determination
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Engineering Cybernetics.
2012 (English)MasteroppgaveStudent thesis
Abstract [en]

The NTNU Test Satellite (NUTS) project, is part of the Norwegian Student Satellite program ANSAT. The goal of the project is to design and launch a double CubeSat by the end of 2014. During earlier satellite projects at NTNU, solid work on design of the attitude determination and control for a small satellite has been done. One of the considered estimation methods for the attitude determination is the extended quaternion estimation method (EQUEST). Further development and testing of the method is described in this thesis. In addition to the new EQUEST method, a nonlinear observer has been implemented and tested. The simulation results for the two methods are compared in order to find the attitude estimation method best suited for the NUTS satellite. The new EQUEST method has several advantages over the more common Kalman filtering for use in small CubeSats. It is less computationally costly, and has a fast startup and settling time. Magnetorquers, which affect the local magnetic field, are used as actuators for the satellite. This makes a fast algorithm preferable, since the attitude estimation and the attitude control should be performed separately. The nonlinear observer is slower than the EQUEST method, but it can guarantee global exponential stability and it is less vulnerable to disturbances. It is therefore introduced as an alternative solution for the attitude determination problem. The original EQUEST method builds upon the QUEST method which has been extended to include non-vectorized terms for gyroscope measurements and attitude prediction in the method’s cost function. In these terms, subtractions between the estimated and measured quaternions are used. The result is not entirely mathematically correct, even though previous testing of the method has been successful. The subtractions in the included terms will not result in new attitude error quaternions. In this thesis, the method is further developed by replacing the subtraction terms with quaternion products. The new method is tested and compared to the original EQUEST method and an extended Kalman filter. It is also compared to the implemented nonlinear observer. If the computational power of the NUTS satellite is sufficiently large, a combination of the developed EQUEST method and the nonlinear observer could be considered for the estimation. A combination of these two attitude estimation methods is implemented and the simulation results are analyzed.

Place, publisher, year, edition, pages
Institutt for teknisk kybernetikk , 2012. , 167 p.
Keyword [no]
ntnudaim:6996, MTTK teknisk kybernetikk
URN: urn:nbn:no:ntnu:diva-18421Local ID: ntnudaim:6996OAI: diva2:565915
Available from: 2012-11-08 Created: 2012-11-08

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