Determination of the spacecraft Foton M-3 attitude motion on measurements of the Earth magnetic field

We present the results of reconstruction of the attitude motion of the spacecraft Foton M-3 during its uncontrolled flight in September 2007. The reconstruction was realized by processing onboard measurements of the Earth magnetic field strength produced by the measurement system DIMAC. The measurement data were accumulated continually during the flight but the processing procedure dealt with data segments, which had length about a few hours. The measurement data on each such segment were processed simultaneously by means of the least squares method and integration of the spacecraft attitude motion equations. The estimates of the mathematical model parameters and initial conditions of the attitude motion were obtained as a result of such processing. The results of processing 16 segments above made clear the motion during the flight. The motion began with very small angular rates, but then it became faster and proved to be close to Euler's regular precession of an axially symmetric rigid body. At the end of the uncontrolled flight, the spacecraft angular rate around its longitudinal axis was equal roughly 0.5 deg./s, projection of the angular rate vector onto the plane perpendicular to that axis was equal roughly 0.18 deg./s.