Residual accelerations on board a designed spacecraft intended for experiments in microgravity sciences are estimated. Three modes of the spacecraft attitude motion are considered: a passive gravitational orientation, an active gravitational orientation, and a single-axis solar orientation. The motion in the first and the second modes is close to a rest position of the spacecraft with respect to the orbital coordinate system, the spacecraft orbit being almost circular one. The motion in the third mode is as follows: the normal to the plane of spacecraft solar arrays is constantly directed to the Sun, the absolute angular rate of the spacecraft is practically equal to zero. The second and the third orientation modes are implemented by electromechanical actuators (a gyro system). At that the third mode provides additionally a decrease of the angular momentum of the gyro system due to the special choice of the spacecraft turning about the normal to the solar arrays. The acceleration estimates are obtained by mathematically modeling the spacecraft attitude motion, taking into account the gravitational and the aerodynamic torques acted upon the spacecraft, as well as the control torques produced by the gyro system.
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