SOFTWARE TOOL DEVELOPMENT FOR TRAJECTORY OPTIMIZATION OF VERTICAL LANDING SPACE VEHICLES

Since the birth of the space industry, the topic of re-usability has been taken into consideration without ever being able to be truly systematically applied to the development of fully reusable spacecrafts. Maintaining an efficient mass ratio for reusable vehicles is a very hard engineering challenge. In fact, launching relative small payload into orbit requires a big quantity of mass propellant, making it inefficient and expensive: re-usability requirements worsen it by adding further subsystems inert mass. However, today, the space industry is witnessing a renewed interest in the development of fully reusable space systems thanks to the to the economic advantages and the increase in safety and environmental sustainability. In this context, this thesis aims to contribute to the technological research in this field, investigating the current state of the art of reusable spacecrafts. The subject matter covering reusable vehicles, from their design to their use, is quite broad: this thesis focuses on vertical landing first stage launchers, that fall into the category of low mechanical energy re-entry spacecrafts. The re-entry problem into the atmosphere of a non-reusable spacecraft is already well known and has been widely addressed over the decades and this knowledge can also be applied to the re-entry of reusable spacecraft. On the contrary, the final descent into the lower atmosphere and the vertical landing differ from typical recovery strategies adopted for non-reusable vehicles. In fact, this phase is critical because it requires active, continuous and precise control of the vehicle to achieve specific position and velocity conditions to complete the landing. These trajectory requirements translate directly into performance requirements for the vehicle, which must be equipped with appropriate control systems such as fins, thrust throttling and thrust vector control. For this reasons this thesis work developed a MATLAB software tool able to compute offline trajectory optimization for final descent and vertical landing. This tool, given specific set of input design parameters of the vehicle, can optimize trajectories respecting the bounds and the constraints imposed by the mission scenario. The software tool is conceived for preliminary mission analysis applications. By studying the trajectory optimization results, vehicle performance requirements can be analyzed to validate the set of input design parameters allowing to preliminary size a reusable first stage launcher and reach the main objective of this thesis work.