Update Scheme for Drag Reference Profiles in an Entry Guidance

Abstract

Entry guidance with an optimal update scheme for the drag reference profile is presented. The guidance is designed for entry in the neighborhood of a specified nominal flight path. To account for off-nominal conditions, the nominal flight path is modified onboard to obtain a reference trajectory for the subsequent guidance cycle. The reference trajectory is adapted to the actual position and velocity. In particular, it provides the range required to reach the target. The reference trajectory is defined as the solution of a variational problem with the objective to stay as close as possible to the nominal entry path. With an appropriate representation of the reference trajectory, the variational problem reduces to an unconstrained quadratic program. This allows for a direct, closed-form solution suitable for onboard application. Rigid-body simulations with model perturbations and modified entry conditions demonstrate the performance of the guidance.