This thesis was performed in The French Aerospace Lab ONERA with the aim to develop a code built in Python for the preliminary sizing of the primary and secondary structures of an hypersonic air-breathing vehicle. The higher demand for space access, in particular regarding the market of small satellites, requires technologies that can be reusable in order to decrease the launch costs. The solutions investigated in this thesis have been the hypersonic air-breathing vehicles. However, the hypersonic flight puts us in front of hurdles due to its extreme environments. This leads us to seek to understand which are the challenges and the advantages of the hypersonic air-breathing vehicles in respect to the rocket-based technologies.