THE DLR REUSABILITY FLIGHT EXPERIMENT (REFEX) – CHALLENGES OF FLYING AN AERODYNAMICALLY GUIDED EXPERIMENT ON AN UNGUIDED SOUNDING ROCKET

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 2022. 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 velocity. 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 cold gas reaction system (RCS) while outside the atmosphere and transitions 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 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. One of the main challenges of the flight experiment is flying ReFEx on top of a VSB-30. The vehicle is not symmetric and has various aerodynamic control surfaces, which protrude the fairing covering the main foldable wings. As such there is a strong coupling between the experiment itself (i.e. the payload) and the launch vehicle during all phases of design. Especially in the early phases, various iteration loops between aerodynamic design, structure, mission design and subsystems where necessary to develop the system design. This paper details some of the challenges faced and how a solution could be found that satisfies both the capabilities of the launch vehicle and the ambitious mission goals.