Angle-of-Attack Modulation in Trajectory Tracking for a Reusable Launch Vehicle

TL;DR

This paper introduces a robust control approach for angle-of-attack modulation in reusable launch vehicles, improving transient entry guidance performance during bank reversals by addressing non-minimum phase behavior and disturbances.

Contribution

It develops a novel feedback linearization control method with disturbance observer for angle-of-attack modulation, enhancing transient response in entry guidance.

Findings

Enhanced transient performance in simulations

Robust control effectively manages disturbances

Improved stability during bank reversals

Abstract

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.