A Rapid Assessment Tool for Space Vehicles in Guidance and Control Performance during Powered Reentry

Abstract

A guidance and control (G&C) design tool to rapidly assess the necessary control effort, and level of fault-tolerance of a conceptual space access vehicle to track its flight trajectory during powered reentry with engine gimbal control is described. For a space access vehicle, a powered reentry with a gimbaled engine provides the vehicle an additional control effector to accommodate unanticipated control effector failures. As a result, control actions and their accompanying trajectories during contingencies are greatly different from those of unpowered reentry. The G&C law has an inner-loop/outer-loop structure. The innerloop control law, based on dynamic inversion with a non-linear control allocator, is used to linearize the vehicle dynamics over its flight envelope and assign control tasks over the available control effectors to track the desired roll rate p ,p itch rateq ,a nd yaw rater .T he outer-loop guidance law is based on backstepping method that transforms the trajectoryrelated flight path angle γ and desired bank angle φ into commands in roll rate pdes ,p itch rate qdes ,a nd yaw raterdes. Assessment of the vehicle’s tracking performance and associated aero-control usage can be made. This tool can be used as part of the preliminary design cycle in configuration, trajectory planning, structural analysis, aerodynamic modeling, control effector choice and sizing, and mode of reentry. Such integrated approach early in the design helps to ensure that the conceptual vehicle will achieve the overall optimal objectives such as high payload fraction, fault-tolerance to control effector failures, and mode of reentry.