Analysis of the Reconfigurable Control Capabilities of a Space Access Vehicle

Abstract

Future access to space vehicles will be required to achieve a high level of safety and operability. In order to achieve these goals, integrated adaptive guidance and control can be used to recover a vehicle from off-nominal conditions, such as control effector failures, engine out, loss of engine gimbal, and so on. In this work, a preliminary configuration for a space access vehicle is defined. The vehicle contains five control surfaces, a bodyflap, two elevons, and two rudders. A guidance and control (G&C) design tool to rapidly assess the necessary control effort of the vehicle to track its flight trajectory is developed. This tool can be used as part of the preliminary design cycle in configuration, trajectory planning, structural analysis, aerodynamic modelling, or control surface sizing. Given the conceptual configuration and a desired trajectory for re-entry flight, this G&C tool provides an inner-loop feedback control law and outer-loop feedback guidance law to track the given trajectory. The inner-loop 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 to the available control effectors to track the desired roll rate, pitch rate, and yaw rate. The outer-loop guidance law is based on a back-stepping method that transforms the trajectory-related flight path angle and desired bank angle into commands in roll rate, pitch rate, and yaw rate. Assessment of the vehicle's ability to recover from control failures is conducted in this work for a nominal re-entry flight. This assessment is used to provide inputs to configuration development to overcome any shortcomings in inner-loop reconfiguration capabilities.