Linear near-equilibrium glide model for unpowered entry trajectory control

Trajectory control plays an essential part in development of entry guidance systems for unpowered gliding entry. From an engineering standpoint, a trajectory control law in a simple structure as well as capable of high adaptability and flexibility is very appealing. To this end, a linear near-equilibrium glide model (LNEGM) is developed using an empirical near-equilibrium glide condition (NEGC). Unlike the prior work on linear approaches, the LNEGM is a flexible model in that it can represent the majority of the linear dynamics of the unpowered gliding entry trajectories. Based on the LNEGM, a linear trajectory control law is naturally obtained, which is composed of a feed-forward part and a proportional-derivative (PD) feedback part. The unique feature of the proposed linear trajectory control law is that the feedback gains are analytical equations associated with desired profiles and transient guidance performance requirements. A state-of-the-art application is given in which the proposed linear trajectory control law satisfactorily solves a common trajectory shaping problem for a class of numerical predictor-corrector guidance.