Minimization of spacecraft attitude error due to wheel speed reversal
AssigneeRCA Corporation
InventorJosef Siegfried Pistiner
Life of this patent
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Abstract
An attitude control system for a substantially zero momentum spacecraft is arranged to minimize the attitude errors during periods of reaction wheel speed reversals. Wheel speed is sensed by a suitable device such as a tachometer or Hall elements. Spacecraft three axis attitude is sensed by suitable sensors such as sun sensors, star sensors, gyroscopes or earth horizon sensors. A control network is provided to generate the wheel torque commands necessary to maintain proper three axis attitude. During periods of wheel speed reversal, the control network includes appropriate compensation terms and corrections to the wheel torque command.
Claims22
An attitude control system for a substantially zero momentum satellite having three mutually perpendicular axes, comprising:
- a. attitude determination means mounted on said satellite for detecting deviations of each of said mutually perpendicular axes from a predetermined reference attitude and generating attitude error signals in response to said detected deviations of said predetermined attitude;
- b. first reaction wheel, second reaction, and third reaction wheels, each of said wheels mounted on said satellite on a respective axis parallel with a respective one of each of said three mutually perpendicular axes, each of said wheels being rotationally di-directional;
- c. control means responsive to said attitude error signals for generating three torque command signals each associated with a respective one of each of said three wheels, each of said torque command signals causing the associated one of said respective wheels to develop control torques and rotate at an angular velocity and direction of rotation to correct and reduce substantially to zero any deviations that are detected;
- d. means responsive to a threshold value of speed of each of said wheels for generating an anticipation signal manifesting an anticipated reversal of rotation of a given wheel;
- e. said deviations from a predetermined reference attitude including deviations caused by torques generated by any of said wheels when operating at relatively low rotational speeds including zero speed, and
- f. means included in said control means responsive to said anticipation signal for altering each of said wheels torque command signals to increase the rate of reduction of said wheel rotation speed to zero and to increase the rate of increase of said wheel rotation speed after said wheel rotation is reversed,
- whereby deviations due to relatively low rotational speeds and stoppage of said wheels are reduced substantially to zero.
A method for controlling the attitude of a substantially zero momentum satellite having three mutually perpendicular axes and first, second, and third rotationally bi-directional reaction wheels each mounted on said satellite on a respective axis parallel with a respective one of each of said three mutually perpendicular axes, comprising the steps of:
- a. detecting deviations on each of said mutually perpendicular axes from a predetermined reference attitude;
- b. generating attitude error signals corresponding to said detected deviations;
- c. generating three torque command signals as a function of said attitude error signals, each of said torque command signals associated with a respective one of each of said three mutually perpendicular wheels, each of said torque command signals causing the associated one of said respective wheels to develop control torques and rotate at an angular velocity and direction of rotation to correct and reduce substantially to zero any deviations that are detected;
- d. comparing the speed of each of said three wheels to a threshold value of speed;
- e. generating in response to said comparing step for speeds equal to or less than said threshold value an anticipation signal manifesting an anticipated reversal of rotation of a given wheel;
- and
- f. altering each of said wheel torque command signals in response to said anticipation signal to increase the rate of reduction of said wheel rotation speed to zero and to increase the rate of increase of said wheel rotation speed after said wheel rotation is reversed,
- whereby deviations due to relatively low rotational speed and stoppage of said wheels are reduced substantially to zero.
Dependencies are inferred from the claim text.