Round-Trip-Engineering, RTE, specifies the process of upgrading a legacy software system to a newer version, by extracting first the model of the existing system, modifying the extracted model and generating eventually new software source code from this updated model. To support the process of reuse and migration of legacy software systems, a study has been initiated by the European Space Agency, ESA to investigate the current state of the available RTE technologies. The outcome of this study is a clearly specified process, based on the Model Driven Architecture approach and compliant with the ECSS software engineering standards. Also a tool chain has been identified, which supports the specified RTE process. As part of this study the application of the process and the usage of the tool chain have been demonstrated successfully on an existing component of the ESA SCOS-2000 System. Nomenclature