Determination of the Spacecraft Foton-12 Attitude Motion on Measurements of the Earth Magnetic Field

The paper presents the results of reconstruction of the spacecraft Foton-12 attitude motion during its uncontrolled flight in September 1999. The motion was reconstructed by processing on board measurements of the Earth magnetic field strength. The measurement data were accumulated almost continually, but the processing procedure dealt with data segments, which had length about a few hours. The measurement data on each segment were processed simultaneously by means of the least squares method and integration of the spacecraft attitude motion equations. The estimations of the mathematical model parameters and initial conditions of an attitude motion were obtained as a result of such processing. The results of processing a few tens of segments above made clear the motion during the whole 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. In last days of flight the spacecraft angular rate around its longitudinal axis was equal roughly 1 deg./s, projection of the angular rate vector onto the plane perpendicular to that axis was equal roughly 0.15 deg./s. Deflections of the longitudinal axis from the normal to orbital plane did not exceed 50 deg. The estimations of real quasi-steady acceleration component on board the spacecraft were obtained.