This paper aims at presenting an improved version of a MDAO (Multi-Disciplinary Analysis and Optimization) tool developed by ONERA in order to support the designer during the initial conceptual design phase of high-speed civil transportation aircrafts. This tool helps to evaluate the long-term sustainability of operative concepts by providing a 0D sizing (maximum take-off mass, fuel mass, dry mass, plan surface, volume, lift and thrust requirements, ticket price per passenger…) corresponding to a specific mission in terms of range (3000 to 18000 km), number of passengers (10 to 300), fuel (biokerosene, LCH4, LH2). The cruise Mach number (3 to 8), supersonic dynamic pressure (20 to 100 kPa), Küchemann parameter are design variables that could be frozen or optimized for each mission. This improved version corrects some weaknesses of the previous version thanks to new models of aerodynamics, propulsion, masses, ascent and descent phases, and it introduces the supersonic dynamic pressure as an additional parameter to optimize. After presenting the sizing tool and the physical and implemented cost models, this paper provides the results and especially discusses the optimized designs obtained for different missions.