Current status of the DLR Reusability Flight Experiment - ReFEx

Abstract

The Reusability Flight Experiment (ReFEx) is being developed by DLR (German Aerospace Center) to provide flight and design data on, as well as operational experience with, a winged first stage of a reusable launch vehicle (RLV). As such ReFEx will be a small technology demonstrator and is slated for launch in 2021. The experiment will be launched on a VSB-30 sounding rocket to altitudes and velocities similar to a first staging event and will then attempt a return flight along a trajectory comparable to a returning winged first stage RLV, transitioning from hypersonic speeds down to subsonic flight. ReFEx is about 2.7 m in length, has a wingspan of about 1.1 m and has a mass of approx. 450kg. It is controlled by a nitrogen cold gas reaction system (RCS) while outside the atmosphere and shall transition to aerodynamic control surfaces (canards and rudder) when atmospheric effects come into play. The maximum Mach number reached during the re-entry manoeuvre is about Mach 5. Besides being able to fly an optimised trajectory (generated autonomously on-board) to reduce the thermal and mechanical loads, ReFEx shall demonstrate manoeuvrability by flying a turn of at least 30° with respect to the original heading measured from entry interface. The entry interface was placed at 60 km altitude for the purposes of this experiment, as the effects of the atmosphere become significant at this altitude for the foreseen trajectory. The key technologies demonstrated in this vehicle are, amongst others: aerodynamic design of a vehicle capable of stable flight through many flow regimes, guidance, navigation and control (GNC) capable of on board generation of an optimised trajectory, the seamless transition between extraand intra-atmospheric flight controls and health monitoring of the vehicle status during flight using advanced sensors such as Fiber Optic Sensors (FOS) and Flush Air Data System (FADS). There has been an extensive planning phase for ReFEx and it has successfully passed SRR (Systems Requirements Review) and entered phase B development in February of 2018. ReFEx is one of the largest flight experiments conducted at DLR and officially became a fully funded project in April of 2018. This paper will give an overview of the current technological as well as the project status and provide some more detailed analysis on the re-entry scenarios studied for the mission.