Achievable Moments NDI-based Fault Tolerant Thrust Vector Control of an Atmospheric Vehicle during Ascent

Abstract

In this article the design of a fault tolerant thrust vector control (TVC) for the automated ascent of the Hopper reusable launch vehicle is presented. The considered ascent starts at the pull-up maneuver performed immediately after horizontal take off and ends at main-engine-cut-off. The TVC law uses nonlinear dynamic inversion (NDI) to obtain the required engine gimbal deflections for robust tracking of the angle of attack and bank angle from a guidance law. The NDI–based TVC is characterized by the use of the Hopper's engine redundancy layout and by the interpretation of NDI as an achievable dynamics identification scheme. The resulting TVC design has been validated using a Monte Carlo campaign with realistic aerodynamic mismatch, corrupted measurements, parametric uncertainty and high fidelity atmospheric and 6DoF vehicle dynamics models. Evaluation of the design with a wide array of thrust and engine gimbal faults yields that the resulting TVC improves the closed loop fault tolerant capabilities.