Magion 5 Atitude Determination
Query Interface for Magion 5 - Magnetic field data
The attitude solution for a spin-stabilized satellite is evaluated from onboard
3-axis magnetometer readings. The method is based on a theoretical approach of
the satellite motion as well as on the behaviour of the geomagnetic field along
the orbital trace. The initial conditions are estimated using a specific parameterization
of the attitude at an initial epoch. A local reference system is defined
with one axis parallel to the direction of the magnetic field vector.
The attitude matrix could be then straightly derived in terms of the Euler
angles up to an unknown initial phase. For a convenient definition
of the local frame, the initial phase is geometrical described as the angle
obtained by coning the main axis of the satellite along the magnetic
field line until it crosses a rectangular plane to the ecliptic one.
The evaluation of the unknown initial Euler angle originates from
the properties of the Earth's magnetic field, when the satellite
is crossing over regions with fast variations of the direction of the
magnetic field line. The kinematic solutions of Euler equations could be established from
gyro data measurements or from a theoretical approach of the satellite motion
in respect with it's mass center.
A batch numerical filter has been developed to search for the best-fit state
parameters and to solve for the solutions of the dynamic and kinematic equations of
motion. The environmental effects due to the solar pressure, gravity and magnetic
disturbance torques as well as the internal passive stabilization torque have been
related to the torque-free attitude solutions of a nutating spacecraft.
Numerical integration methods based on ordinary differential
equations techniques have been tested for the truncation errors and also
for their stability in the attitude minimization algorithm.
The accuracy of the method depends on the correct estimates of external and
internal torques acting on the satellite, on the exactness of the geomagnetic
field model and on the accuracy of the onboard measurements.
The method was applied for a spin-stabilized satellite. Magion-5 as a
small subsatellite with 65 degrees inclination orbit and a perigee of 20000 Km,
was intended for carrying out simultaneously measurements with the Auroral
Probe main satellite, in the framework of Interball project.
Contact: Dr. Horia Comisel
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