Development and Comparison of Estimation Methods for Attitude Determination
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 methods 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.
ntnudaim:6996, MTTK teknisk kybernetikk
IdentifiersURN: urn:nbn:no:ntnu:diva-18421Local ID: ntnudaim:6996OAI: oai:DiVA.org:ntnu-18421DiVA: diva2:565915
Fossen, Thor Inge, Professor