Abstract: A method and system are provided for electronically steering a phased array antenna mounted on a spacecraft to reduce or eliminate pointing error by modifying the phased array steering commands in a way that compensates for the offset, even on yaw steered spacecraft whose antenna beams must be de-yawed to minimize the movement of spot beams pointed to the surface of the Earth. Electronic offset pointing on de-yawed phased array antennas is achieved by computing a set of pointing control parameters on the ground, and uplinking the parameters for final processing on-board the spacecraft. The control parameters are derived so that only minimal changes to the on-board processing capabilities are required relative to a de-yawing control arrangement alone.

Abstract: 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.