ReFEx: Reusability Flight Experiment - Architecture and Algorithmic Design of the GNC Subsystem

Abstract

The German Aerospace Center (DLR) "Reusability Flight Experiment" (ReFEx) aims to demonstrate the Guidance, Navigation, and Control (GNC) capabilities for an aerodynamically controlled Reusable Launch Vehicle (RLV) stage. The GNC subsystem is responsible for maintaining stability and steering the vehicle to achieve a target state, specifically transitioning from the supersonic to subsonic flight regime. This objective is accomplished through: 1) planning and updating a feasible trajectory from separation up to the target state (Guidance); 2) estimation of the vehicle’s current state by leveraging sensor measurements (Navigation); and 3) tracking the guidance’s attitude commands while maintaining vehicle’s stability using the actuators (Control). This paper provides a comprehensive overview of the algorithms employed within these modules, their integration into the GNC architecture, and an evaluation of their performance. The results demonstrate that the GNC algorithms meet the requirements, while acknowledging the need for further improvements in the accuracy of the navigation solution. By showcasing the GNC capabilities of the ReFEx project, this research contributes to advancing the field of aerodynamic control for RLV stages.