Analysis of Low Frequency Microgravity Environment On Board the Foton-11

The paper presents the methods and results of the investigation of low frequency microgravity environment on board the Russian spacecraft <i>Foton-11</i>. The investigation is based on processing the angular rate measurements obtained by the German system QSAM and the acceleration measurements obtained by the system QSAM and the French accelerometer BETA. Processing was in follows. First, a low frequency component was filtered from angular rate and acceleration measurement data. Frequencies of filtered data didn't exceed 0.02 Hz. Then each vector component of the filtered angular rate or acceleration was fitted by an analogous function calculated along a solution of spacecraft attitude motion equations. The appropriate solution was found by the least squares method with estimation of its initial conditions, some parameters in the motion equations and constant biases in filtered data. Fitting was made on time intervals from an hour up to 5 hours. Processing three different kinds of data gave similar results. The spacecraft attitude motion proved to be close to Euler's regular precession of an axially symmetric rigid body during almost the whole 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 0.2 deg./s. Each component of the angular rate vector in the approximating solution was fitted to measurements with the mean square error of 0.04 deg./s. Absolute values of the quasi-steady acceleration component at the places of the accelerometers didn't exceed of 5 · 10^-5 - 10^-4 m/s₂. Each component of the acceleration vector calculated by means of the approximating solution was fitted to measurements with the mean square error of 5 · 10^-6 m/s₂.