Fixed-trim re-entry guidance analysis

Abstract

The terminal guidance problem for a fixed-trim re-entry body is formulated with the objective of synthesizing a closed-loop steering law. A transformation of variables is made that reduces the order of the state system for the guidance problem, and a subsequent linearization with motion along the sight line to the target as a reference produces a further order reduction. The final, reduced-order system, although nonlinear and time-varying, is simple enough to lend itself to synthesis of a class of guidance laws. A generalization of the feedforward device of classical control theory is successfully employed for compensation of roll-autopilot lags. A comparison with existing fixed trim guidance laws is carried out computationally with a simulation model idealizing the navigation and control systems as error-free. The proposed guidance law exhibits superior miss-distance performance in the comparison.