The Effects of Momentum Bias on a Gravity Gradient Stabilized Spacecraft with Active Magnetic Control

The improvements achieved by adding a momentum bias wheel to a Gravity Gradient (GG) stabilized spacecraft are evaluated. Mass, power, and computational processing requirements, as well as performance, are compared for three Attitude Determination and Control Subsystem (ADACS) scenarios. Spacecraft which require low mass and power have long Incorporated GG torques as a passive stabilization technique. The spacecraft is oriented in the general direction required by the mission, but the overall attitude and attitude rate errors are not exceptionally tight. In order to improve the spacecraft pointing accuracies the GG stabilized ADACS .can be augmented by an active control technique. Previously, the use of three TORQRODs was evaluated. With one oriented along each of the spacecraft axis. For this analysis, the incorporation of a small momentum bias wheel is shown to significantly improve the magnetic attitude control from a few degrees to a few tenths of a degree by providing additional gyroscopic stiffness. The ADACS impacts of a constant speed wheel vs an active pitch control loop are also compared. Attitude control techniques are one part of the overall ADACS solution. The knowledge of how well the spacecraft attitude can be determined defines the net ADACS performance for a given mission scenario. If an accuracy of few degrees is sufficient a novel approach is to determine the attitude simply from three-axis magnetometer data. The addition of an Earth horizon sensor to provide accurate roll and pitch information can Improve the overall ADACS performance to approximately 0.5 , but at the expense of Increased mass and power requirements.