The German Aerospace Center is currently developing a flight experiment as a technology demonstrator for a reusable, Vertical Take-off and Horizontal Landing (VTHL) booster stage, the Reusable Flight Experiment (ReFEx). This project allows development progress on several sub-systems and their interaction, generating the know-how needed to actually fly a VTHL booster stage. A two-staged VSB-30 sounding rocket transports ReFEx to an altitude of about 130 km. After the separation from the carrier rocket, an autonomous re-entry is performed with a maximum Mach number (M) of approx. 5. The first part of the following re-entry will be flown upside down at high, negative angles of attack (α), for the initial deceleration, to keep the structural and aerothermal loads within acceptable limits and to provide lateral stability. At M ≈ 1.5, a 180° roll maneuver will be performed to reach the nominal orientation close to α = 10° for a maximum lift to drag ratio.
One major task covered by the Spacecraft Department of the DLR-Institute of Aerodynamics and Flight Technology in this project is the aerodynamic design of ReFEx. The design process was dominated by several boundary conditions, most prominently by the ballistic VSB-30 launch vehicle with its constrained dimensions. To avoid the ascent difficulties a fairing will be used to cover the wings. The latter are folded to fit under the fairing (Fig.1).
Numerous design loops, with all involved disciplines e.g. the structural and thermal loads, increased the confidence in the geometry. The resulting geometry is aerodynamically stable during both the ascent and the re-entry. For the entire re-entry segment the controllability of the vehicle is ensured. Extensive datasets are needed to lay out the vehicle itself, the flight range for the trajectory and the control systems. The calculations of these aerodynamic data sets for the whole flight range are the second big task of the spacecraft department. Beside these main working fields, the focus of the institutes work in the REFEx project lays on the enhancements of existing methods, like the flight mechanics coupling (CoNF²aS²).