ABSTRACT
Chapter 4 discusses spacecraft dynamics and modeling. Section 4.1 presents a general model for spacecraft system. This model can be divided as the dynamics model and the kinematics model. The spacecraft model discussed in this section has a significant difference from existing quaternion-based spacecraft models, i.e., the kinematics model uses the reduced quaternion model. The merit of using reduced quaternion models is that the linearized spacecraft models are controllable while the spacecraft models using full quaternion are not. It is well-known that all modern linear control system design methods require that the systems are controllable. This makes the reduced quaternion spacecraft model very attractive. Based on the general spacecraft model, two important special models are discussed. Section 4.2 is about the inertial pointing spacecraft model, and section 4.3 presents the nadir pointing momentum biased spacecraft model. These two models correspond to the ideal pointing directions for most spacecraft missions. While the nadir pointing model considers only one momentum wheel, the model can easily be extended to have three wheels aligned to the body frame.
