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This paper presents a multidisciplinary analysis tool STSOPT for the simultaneous trajectory and system optimization of reusable launch vehicles. This software package has been developed at the Space Systems Institute, University of Stuttgart over 20 years. The tool has been revised fundamentally, updated and improved both from the algorithmic and software point of view while maintaining the principal methodology, model assumptions and the system dynamics for the flight simulation. The flexibility and performance increase achieved is demonstrated by using this software package to perform system analyses of the partly-reusable launch vehicle Hopper -the central concept of the German technology program ASTRA (Selected Systems and Technologies for Future Space Transportation Applications). Hopper consists of a reusable, unmanned, and winged main stage and an expendable upper stage. The main stage is powered by three cryogenic Vulcan 3 engines -a future version of the Ariane 5 main engine. The upper stage is powered by a cryogenic Vinci engine.