M.Sc Thesis

M.Sc StudentKoren Amir
SubjectIntegrated Guidance-Control of Highly Maneuverable Missile
with On-Off Actuators
DepartmentDepartment of Aerospace Engineering
Supervisors ASSOCIATE PROFESSOR Moshe Idan
DR. Oded Golan
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Flight control and guidance loops are commonly designed separately, assuming spectral separation. During the end-game phase of the interception, the spectral separation assumption is often not valid due to fast relative geometry changes. Consequently, a two-loop design may fail to provide desired interception accuracies.

Integrated guidance-control design schemes for the end-game phase of the encounter have been proposed in order to improve the interception performance. The improved performance is achieved by addressing the coupled nonlinear interception problem, involving both nonlinear kinematics and dynamics. Inherent uncertainties of the problem, resulting from unknown target maneuvers and interceptor modeling errors, require a robust nonlinear control design methodology for the integrated guidance-control synthesis.

Sliding-mode-control (SMC), a nonlinear robust control design approach, was recently introduced for integrated guidance-control loops of agile missiles in the final interception phase. Zero-effort-miss-distance (ZEM), commonly used in differential game formulations of guidance problems, was selected as the sliding surface. The controller demonstrated high interception accuracies when tested for missiles with simplified linear actuators. The current study extends this analysis to more realistic actuation dynamics. Specifically, we examine on-off actuation of short range air-to-air missiles that typically use pneumatic actuators to control their aerodynamic surfaces. Pneumatic actuators are used due to their high power to weight ratio. However, their on-off operation leads to an oscillatory motion of the control surface around its commanded position, which may cause degraded interception performance.

The main goal of this study is to examine the interception performance of the integrated SMC design for interceptors with a pneumatic actuator, and compare it to a conventional two-loop design. In addition, we present the end-game region of attraction, which defines the initial conditions for which the missile will reach the ZEM surface in finite time, indicating interception. This analysis is performed assuming worst case uncertainties and most stringent target maneuvers. The region of attraction dictates performance requirements for the mid-course guidance system for efficient utilization of the integrated end-game guidance-control scheme.

Interception performance was evaluated through a Monte Carlo study. The results clearly demonstrate the superiority of the integrated design over the two-loop design. In both designs, performance is degraded when a pneumatic (oscillating) actuator is used instead of a linear one. However, the integrated design shows a dramatically lower sensitivity to the actuation characteristics and the control surface oscillations. These favorable results of the integrated design are accredited to the robustness of the SMC method.