Passivity Analysis for Non-Linear, Non-Stationary Entry Capsules: Translational Motion

Abstract

AbstractApplication of simple adaptive control (SAC) theory to the design of guidance and control systems for winged re-entry vehicles has been proven successful, despite the fact that the sufficient conditions of passivity are not fulfilled throughout the trajectory. To continue the analysis of passivity of non-linear, time-varying systems we study an entry capsule that enters the atmosphere in a lift-down configuration to avoid skipping flight, and which is controlled by a reaction control system only. Since the transient effect is an important factor in the stability properties of the guidance system, we will set up an analysis methodology that takes both the non-linearities and the time-varying aspects due to the strongly changing flight regimes into account. Deriving the passivity conditions for translational motion, and evaluating these conditions along the trajectory shows that the entry capsule is not almost strictly passive, and the sufficient conditions are not met. However, based on past experience of similar (and even more complex) systems, SAC can still be applied under a wide range of operating conditions, perturbations and even control saturation.