Future launch vehicle concepts and technologies for expendable and reusable launch vehicles are currently investigated by the DLR research project AKIRA, focusing on vertical takeoff and horizontal landing (VTHL), as well as horizontal takeoff and horizontal landing (HTHL) concepts.
Dedicated developments of multidisciplinary frameworks for launch vehicle modeling and preliminary design optimization have been presented in the relevant literature. Moreover, it is common that these activities are performed by several independent, discipline-specific tools. With such an approach, only a limited amount of interactions of the involved disciplines with the overall system dynamics can be accounted for.
This paper focuses on the multidisciplinary launch vehicle guidance, control, and dynamics modeling framework that has been developed at DLR-SR in support of the aforementioned reusable launch vehicle design activities taking into account highly interconnected disciplines (propulsion, aerodynamics, and GNC, amongst others) and changing environmental conditions. The modeling framework is based on the object-oriented, multi-disciplinary, and equation-based modeling language Modelica. In this paper, dedicated 3-DoF and 6-DoF models, covering the kinematics and dynamics formulation, environmental effects, aerodynamics, and propulsion models for system dynamics analyses, trajectory simulations and GNC design are presented.
In particular, we showcase the advantages of using nonlinear inverse models obtained automatically by Modelica. This method establishes a direct connection between 3-DoF and intermediate 6-DoF models considering trajectory optimization results provided by the DLR Trajectory Optimization Package `trajOpt'. With this approach, angular rates and resulting moments can be obtained by the intermediate 6-DoF model for subsequent controllability analyses. The benefits of our modeling framework are discussed in terms of future GNC design and trade-off studies.