Abstract: A spacecraft (10) includes and attitude sensor (16) for generating sensed attitude signals. A controllable drive arrangement (238) is coupled to a reaction wheel (46), for driving it in response to speed error signals. The drive results in changes in reaction wheel speed. The spacecraft has a digital speed sensor (248) coupled to the reaction wheel, for generating quantized speed signals. A reaction wheel speed error signal generator (234) produces speed error signals in response to the difference between the attitude command and the sensed attitude signals, corrected by signals responsive to the speed of the reaction wheel, whereby at low reaction wheel speeds, the quantization causes attitude errors.

Abstract: A spacecraft (8) includes a movable appendage such as solar panels (12) operated by a stepping motor (28) driven by pulses (311). In order to reduce vibration andor attitude error, the drive pulses are generated by a clock down-counter (312) with variable count ratio. Predetermined desired clock ratios are stored in selectable memories (314a-d), and the selected ratio (R) is coupled to a comparator (330) together with the current ratio (C). An up-down counter (340) establishes the current count-down ratio by counting toward the desired ratio under the control of the comparator; thus, a step change of solar panel speed never occurs. When a direction change is commanded, a flag signal generator (350) disables the selectable memories, and enables a further store (360), which generates a count ratio representing a very slow solar panel rotational rate, so that the rotational rate always slows to a low value before direction is changed. The principles of the invention are applicable to any movable appendage.

Abstract: A vibration suppression system senses undesired mechanical motion of a body, and continuously drives a proof mass actuator system to reduce disturbances. An inertial or relative displacement sensor is processed to determine the energy content of the motion, and a correction signal is generated which is summed with the actuator drive signal to minimize the sensed motion energy. The position of the proof mass is sensed, and processed by differentiating and scaling, and the processed proof mass position signal is also summed with the actuator drive signal. The system causes the proof mass actuator loop natural frequency to tend to track the frequency associated with the maximum vibrational energy.

Abstract: A satellite attitude control system is usable in the absence of any inertial yaw attitude reference, such as a gyroscope, and in the absence of a pitch bias momentum. Both the roll-yaw rigid body dynamics and the roll-yaw orbit kinematics are modelled. Pitch and roll attitude control are conventional. The model receives inputs from a roll sensor, and roll and yaw torques from reaction wheel monitors. The model produces estimated yaw which controls the spacecraft yaw attitude. The model further produces estimates of the constant component of the disturbance torques for compensation thereof.

Abstract: A satellite attitude control system is usable in the absence of any inertial yaw attitude reference, such as a gyroscope, and in the absence of a pitch bias momentum. Both the roll-yaw rigid body dynamics and the roll-yaw orbit kinematics are modelled. Pitch and roll attitude control are conventional. The model receives inputs from a roll sensor, and roll and yaw torques from reaction wheel monitors. The model produces estimated yaw which controls the spacecraft yaw attitude.

Abstract: A reaction-wheel stabilized spacecraft reduces attitude errors at wheel reversals by application of a dither component to the wheel torque command signal.