A method comprises: launching observation means configured to observe upper air environment immediately before launching an airship to acquire ambient air data on the actual conditions of the upper ambient air including altitude, pressure, wind direction, wind speed and temperature; determining an ascension profile for the airship by simulation using the ambient air data on the actual conditions of the ambient air; determining an initial quantity of Helium gas conforming to the actual conditions of the ambient air; and adjusting the quantity of Helium gas in the Helium room to the initial quantity of Helium gas to set an initial buoyancy. The method sets hull parameters for the hull of the airship to provide an ascension profile conforming to the actual conditions of the ambient air.