Abstract: An attitude control system for a three-axis controlled spacecraft (1) in which the location of thrusters causes significant cross-coupling torques. A thruster command conditioning electronics module (TCCEM) (3) is positioned between the conventional roll, pitch, and yaw loop controllers (41-43) and the thrusters (61-63). The TCCEM (3) converts spacecraft-axis-based torque requirement signals (TDX, TDY, TDZ) emanating from the loop controllers (41-43) into scalar quantities (UL, UM, UN) that are input to thruster modulators (51-53) that turn on one or more thrusters of the thruster pairs (L,M,N). The TCCEM (3) causes the spacecraft (1) attitude to be adjusted as commanded by the torque requirement signals (TDX, TDY TDZ) despite the presence of the cross-coupling. Two embodiments are illustrated: a working embodiment in which cross-coupling torques are produced about two axes (Y,Z), and a more general embodiment in which cross-coupling torques are present about all three axes (X,Y,Z).

Abstract: Mechanical oscillations of a mechanism containing a stepper motor, such as a solar-array powered spacecraft, are reduced and minimized by the execution of step movements in pairs of steps, the period between steps being equal to one-half of the period of torsional oscillation of the mechanism. Each pair of steps is repeated at needed intervals to maintain desired continuous movement of the portion of elements to be moved, such as the solar array of a spacecraft. In order to account for uncertainty as well as slow change in the period of torsional oscillation, a command unit may be provided for varying the interval between steps in a pair.