Definition of Requirements for Horizontal Landing of a Re-entry Vehicle

The growing interest in reusable space transportation systems has renewed the focus on horizontal landing capabilities for re-entry vehicles. While parafoil-assisted recovery remains a widely studied and applied method, particularly for small-scale or experimental platforms, current trends in aerospace engineering and spaceflight operations emphasize the need for autonomous runway landings to improve operability, reusability, and mission flexibility. Within this context, lifting-body and winged configurations are increasingly regarded as viable solutions, although the minimum aerodynamic and performance requirements for their final approach and landing remain insufficiently defined. This thesis addresses this gap by developing a methodology to identify the fundamental requirements that a re-entry vehicle must satisfy— in terms of L/D ratio, L/W ratio, and other aerodynamic performance metrics—to successfully perform a controlled horizontal landing on a runway without the need for parafoil systems. To support the analysis, a simplified automatic guidance model was implemented, enabling the simulation of the terminal descent and landing phase under various aerodynamic configurations and constraints. A central component of this research is the implementation of an optimization framework to evaluate vehicle behavior and validate the feasibility of safe runway landing for representative design cases. Optimization methods are a cornerstone in aerospace design, as they allow the systematic treatment of nonlinear dynamics, operational constraints, and multi-objective trade-offs. In this work, the Sequential Quadratic Programming algorithm, as implemented in SNOPT, was adopted. SNOPT is particularly suited for large-scale constrained optimization problems, where sparsity in the constraint Jacobian can be exploited to achieve computational efficiency. Its robustness and flexibility make it a standard tool in trajectory optimization and guidance problems, enabling the incorporation of realistic aerodynamic models, vehicle dynamics, and operational constraints within a unified optimization environment. In the proposed formulation, the optimization parameters are defined as the time- dependent deflection angles of two control surfaces, which directly influence the aerodynamic forces and moments during the final approach. By optimizing these control inputs, the guidance model is capable of adapting the trajectory to meet runway-landing requirements while satisfying aerodynamic and dynamic constraints. The optimization process was carried out within a 3-DOF simulation environment, which provided a computationally efficient yet sufficiently accurate representation of the vehicle’s motion during the terminal phase. The underlying model was initially inspired by the Space Shuttle and subsequently generalized to encompass generic winged-body and lifting-body configurations, thereby ensuring the applicability of the methodology to a broader class of reusable re-entry vehicles. The outcome of this research is a comprehensive mapping of requirements for the final re-entry and landing phase, offering a set of guidelines that can inform the preliminary design of future reusable vehicles. By combining aerodynamic modeling, automatic guidance, and advanced optimization tools such as SNOPT, the thesis contributes to the broader development efforts toward more versatile and fully autonomous re-entry systems, thereby supporting the long-term vision of cost-effective and operationally flexible space transportation