Stability analysis and flight control design of the winged reusable launch vehicle ReFEx

The German Aerospace Center (DLR) is currently studying different technologies for reusable launch vehicles (RLVs) to evaluate and compare their benefits. The project CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss-back Operations) investigates a VTVL (vertical takeoff, vertical landing) concept. In the DLR project ReFEx (reusability flight experiment), in the context of which this paper is presented, a winged VTHL (vertical takeoff, horizontal landing) concept is investigated to develop the key technologies for future winged RLV applications, culminating in a flight experiment to demonstrate the capability of controlled autonomous return flight from supersonic to subsonic speeds. In this paper, analysis of stability and controllability is used on a three-dimensional envelope of points to derive a suitable flight corridor for the re-entry. Second, a controller concept based on inversion of the rotational equations of motion is derived. The validity of the presented controller concept is shown on a preliminary level via comparison of open-loop and closed-loop dynamics at two representative flight points and a time simulation which includes a segment of the planned mission.