Chapter 7: Attitude Determination and Control

7.1 Introduction

In this chapter we discuss what is often considered to be the most complex and least intuitive of the space vehicle design disciplines, that of attitude determination and control. The authors agree with this assessment, but would add that the more complex aspects of the subject are of primarily theoretical interest, having limited connection with practical spacecraft design and performance analysis. Exceptions exist, of course, and will be discussed here because of their instructional value. However, we believe that the most significant features of attitude determination and control system (ADCS) design can be understood in terms of rigid body rotational mechanics modified by the effects of flexibility and internal energy dissipation. At this level, the subject is quite accessible at the advanced undergraduate or beginning graduate level.

Even so, we recognize that the required mathematical sophistication will be considered excessive by many readers. Attitude dynamics analysis is necessarily complex due to three factors. Attitude information is inherently vectorial, requiring three coordinates for its complete specification. Attitude analysis deals inherently with rotating, hence noninertial, frames. Finally, rotations are inherently order dependent in their description; the mathematics that describes them therefore lacks the multiplicative commutativity found in basic algebra.

In the following discussion, we attempt to alleviate this by appealing to the many analogies between rotational and translational dynamics and, as always, by stressing applications rather than derivations of results. Those requiring more detail are urged to consult one of the many excellent references in the field. Hughes ^[1]