Methodologies and tools for the analysis of the descent and re-entry phase of a reusable access to space vehicle

In recent years, the space sector has experienced significant growth, both economically and culturally. Investments in space technologies have surged with the emergence of new players and start-ups, marking the beginning of the New Space Economy. This development has led to increased demand for access to space. However, the high cost and relatively low reusability of current launch vehicles remain the main obstacles to further evolution of space exploration. The future of space exploration also depends on the development of reusable and sustainable spacecrafts. Therefore, the creation of a methodology for the design of Reusable Launch Vehicles (RLVs) is essential. In this context, this thesis is part of a research project at the Polytechnic of Turin aimed at developing a software tool for the conceptual design of space missions involving reusable vehicles. This tool aims to support researchers and engineers during the initial design phases. The present work was conducted in parallel with two other colleagues, whose theses focus on the conceptual design of the ascent phase and the creation of a sizing methodology for a reusable SSTO vehicle with Horizontal Takeoff and Horizontal Landing (HTOL) capabilities. This thesis investigates the conceptual study of atmospheric re-entry dynamics of a reusable Single-Stage-to-Orbit (SSTO) vehicle. The main focus is on understanding the complex interaction between aerodynamic forces, thermal loads, and stresses during re-entry. After introducing the typical classes of re-entry vehicles and the atmospheric entry problem, an extensive study of re-entry aerodynamics was conducted. This included an analysis of the aerodynamic coefficients of the main re-entry vehicles built to date. Aerodynamic databases correlating lift and drag coefficients and lift-to-drag ratio with Mach number and angle of attack have been studied. The dynamic of re-entry was then studied by formulating equations of motion with simplifying assumptions. In particular, the planar equations of motion were analyzed, which are sufficient at this level of detail to study the main quantities involved during re-entry. The vehicle was modeled as a point mass with aerodynamic properties and these equations were solved using the fourth-order Runge-Kutta method to obtain trends for key variables such as velocity, Mach number, dynamic pressure, and heat rate. Subsequently, the re-entry corridor for the SSTO was developed, establishing aerothermodynamic constraints (heating rate, acceleration, dynamic pressure) that the vehicle must satisfy during descent. Furthermore, the design of the Thermal Protection System (TPS) was investigated, starting with the description of possible concepts of reusable TPSs. The vehicle wall temperature trend was then calculated to ensure adequate thermal protection during re-entry by balancing the incoming heat flux with the radiant heat flux emitted to the outside environment. The developed methodology was applied to the case study of the Skylon SSTO, which is under development by the British company Reaction Engines Limited (REL). Skylon uses the Synergetic Air-Breathing Rocket Engine (SABRE), a promising type of engine for missions involving SSTO vehicles. Finally, a mission simulation was performed using ASTOS software to validate the results of the design methodology used in this work.