Method and apparatus for spacecraft wheel desaturation

摘要

A method and apparatus are provided that effect spacecraft wheel desaturation by controlling the magnetic torquers aboard the spacecraft. An attitude control system energizes a magnetic torquer coil or set of magnetic torquer coils using a power source having an initial polarity and then monitors the spacecraft's response to the torque created by the coil's magnetic field. By measuring the spacecraft's response to the torque created by the energized magnetic torquers, the direction of the earth's magnetic field is determined. Once the direction of the earth's magnetic field is known, the proper polarity may be applied to the coil to achieve the desired torque. The control system of the present invention synchronously demodulates the craft's angular velocity, estimated from signals obtained from the attitude sensors, using a small dither signal that is superimposed on the control current used to energize the magnetic torquer coil. The result of the synchronous demodulation yields information as to the direction of the earth's field which is then used to control the polarity of the coil energizing power source. Thus, the magnetic torquers are used to achieve a torque that opposes the torque created by the reaction wheels to effect wheel desaturation without the need for the complex and weight-intensive magnetic field measuring and estimating equipment used in conventional attitude control systems.