Pre-sizing and mission optimization of an orbital refueling station

This thesis presents the work carried out during the internship in Thales Alenia Space (Cannes, France), whose subject was the analysis of on-orbit refueling for lunar-bound spacecrafts. Missions towards the moon are one of the main targets of the space market in the next decades. More and more entities, both public and private, are starting to study and develop lunar missions. Reaching the moon, however, requires high quantities of propellants that limit the mass of the spacecraft at the launch. For this reason, space agencies and private companies are starting to study the possibility of refueling spacecrafts in orbit, in order to reduce the mass at launch (and therefore the mission cost) and enhance reusability of modules in orbit. The objective of the present study is to design a Propellant Depot used for in-orbit refueling and to optimize its operational orbit. The study was divided into three parts. Firstly, a bibliography study was carried out, to gather all the relevant information, in particular concerning themes like electric propulsion or in-orbit propellant transfer. Then, the functional analysis was performed, to define the requirements, functions and general architecture of the system. This was done following the MBSE (Model Based System Engineering) approach. The second part consisted in the pre-sizing of the orbiting refueling station (Propellant Depot) itself, based on sub-systems trade-offs and sizing following the requirements. Contextually, the main issues and technological limits were addressed, like the long-term storage of cryogenic propellants or the electric propulsion of heavy spacecrafts. Thanks to this phase, it was possible to provide a possible architecture of the Propellant Depot and therefore estimate the amount of propellant that the system could store. Finally, during the third phase, the approach used in the second part was applied to a large set of possible missions and operational orbits, to determine the optimal application of the Propellant Depot. The results highlighted an optimal mission configuration, which maximized the number of times the system could refuel lunar-bound spacecrafts: thanks to these results, it will be possible to study more accurately the costs and general architecture of lunar missions.