Stability, Pointing, and Orientation

Abstract

This chapter gives an overview of the attitude determination and control system (ADCS) of spacecraft, focusing on small satellites. The ADCS is an important subsystem to insure satellite orientation stability and accuracy of pointing various payloads at specific targets. The introductory section will give an overview of the active ADCS feedback loop and lists some requirements and typical control methods utilized. The next section presents some background theory in attitude dynamics, kinematics, and the significant external disturbance torques in low earth orbit (LEO). Then some techniques used for angular rate and attitude determination are presented, followed by the control laws for magnetic detumbling and reaction wheel attitude control. A complete section is dedicated to a practical example of the calculations to determine the pointing accuracy and stability of a high-resolution (Hi-Res) imaging payload on a minisatellite. Finally the chapter concludes with examples and specifications of typical ADCS sensor and actuator hardware that are commercially available.