Development, Implementation and Testing of Two Attitude Estimation Methods for Cube Satellites
As a part of the CUBESAT project at the Norwegian University of
Science and Technology (NTNU), this paper studies development and
comparison of attitude estimation methods for small cube satellites using
low-cost sensors. The algorithms are based on data from two vectorized
measurements as well as a gyroscope.
In this paper a new method for attitude estimation has been de-
veloped based on QUaternion ESTimation (QUEST). A major concern
with QUEST is that it cannot handle non-vectorized measurements such
as gyroscope data. Substantial improvements have been made to fuse
vectorized and non-vectorized measurements, making the new Extended
QUaternion ESTimation (EQUEST) more suitable for attitude estima-
tion. The well known Extended Kalman Filter (EKF) is derived and
implemented for comparison. Both methods have been developed and
simulated in MATLAB. The code have been rewritten using C language.
The methods are compared both theoretically and experimentally with
implementation and testing on an AVR microcontroller. Minimum power
usage and number of arithmetic operations were considered during the
Testing indicates that the EKF provides a smoother estimation than
the newly developed EQUEST. In contrast to EQUEST, the EKF is
able to estimate the magnetometer and accelerometer bias. However, the
EQUEST has a signicantly faster settling time and is less computational
costly. Compared to the EKF, EQUEST runs more than 5 times faster.
It also requires only 8% of the arithmetic operations of the EKF. Another
disadvantage with the EKF is tracking problems that occur when the two
vectorized measurements are close to parallel. With vectors close to paral-
lel, the mathematical formulation of the EKF makes tracking of a rotation
around the parallel axis extremely dicult. These diculties are hardly
observed in the EQUEST algorithm, which makes it very attractive for
The attitude control of CUBESATs is often done by magnetorquers,
which will aect the local magnetic eld. Hence, control and estimation
should not be done simultaneously, resulting in the estimation and control
switching on and o. For this reason, the long settling time of the EKF
makes the EQUEST even more attractive.
The results in this paper indicate that the newly developed EQUEST
is highly suitable for projects with either limited budget, space, weight or
Place, publisher, year, edition, pages
Institutt for teknisk kybernetikk , 2011. , 119 p.
ntnudaim:5925, MTTK teknisk kybernetikk, Reguleringsteknikk
IdentifiersURN: urn:nbn:no:ntnu:diva-13274Local ID: ntnudaim:5925OAI: oai:DiVA.org:ntnu-13274DiVA: diva2:436732
Gravdahl, Jan Tommy, ProfessorJohansen, Tor Arne