Aerodynamic Behavior of a Descending Launcher First Stage Demonstrator with Grid Fins in the Aerodynamic Phase

In the Horizon Europe Project SALTO, a demonstrator of a vertically landing first stage with three Prometheus engines was investigated, the so-called T3. It shall be recovered with a downrange landing approach. In this paper the aerodynamic phase of the descent trajectory was investigated using wind tunnel experiments of the full launcher configuration in the Trisonic Wind Tunnel Cologne (TMK). The grid fins showed to be efficient to trim and control the vehicle. Increasing the size of the grid fins by 10% does not directly transfer into a larger trimmability region. Modelling of the engine nozzles with closed surfaces is acceptable for low fidelity databases but introduces slight deviations with respect to modelling them as open cavities. A Reynolds number variation showed a small effect of the Reynolds number on the force and moment coefficients. A superposition approach defined in earlier work was validated with the wind tunnel data. In the ascent configuration the deployed grid fins mainly generate additional axial force but do not alter the pitch moment substantially.