  This paper deals with the problem of angle-of-attack modulation with the aim
of enhancing transient performance of entry guidance during bank reversals,
while compensating adverse effects of fast time-varying transient disturbances.
An extended single-input/single-output system is developed in the velocity
domain by means of a dynamic extension technique, and explicitly captures the
trajectory dynamics of angle-of-attack modulation. A normal form for this
extended system is derived for the sake of employing a feedback linearization
controller. Further, the control characteristics of angle-of-attack modulation
is found to be a non-minimum phase behavior under two common conditions in a
near- equilibrium glide flight. Therefore, the issue of angle-of-attack
modulation is formulated as robust output stabilization of the non-minimum
phase system. A disturbance observer-based feedback linearization technique is
used to design a robustly dynamical output-feedback controller for
angle-of-attack modulation, and an internal-state feedback controller for
bank-angle modulation is used to stabilize the unstable internal dynamics.
Numerical simulations are conducted to demonstrate that the performance of the
proposed method of angle-of-attack modulation is enhanced compared to the
existing shuttle method.
