Realization of spacecraft attitude motion with small residual accelerations by electromechanical actuators

We estimate residual accelerations on board a projectible spacecraft intended for experiments in microgravity sciences. Two modes of the spacecraft attitude motion are considered: a triaxial solar orientation and a triaxial orbital orientation. The motion in the first mode is as follows: the normal to the plane of spacecraft solar arrays is constantly directed to the Sun. The motion in the second mode is a rest position with respect to the orbital coordinate system. At that, the spacecraft longitudinal axis is directed along the local vertical, the solar arrays lay in the orbital plane. Both orientation modes are realized by electromechanical actuators (a gyro system). The acceleration estimates are obtained by mathematical modeling of 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. The estimates show that accelerations in the working area of the spacecraft are not more than 10$^{-5}$ m/s$^2$. The orbital orientation of the spacecraft provides a small variation area of the residual acceleration vector, but an electric current from the spacecraft solar arrays is acceptable in this mode only when the Sun is far enough from the orbital plane.