Large groups of the population in Europe encounter significant difficulties in taking part in everyday life due to their functional limitations. The NADIA (NAvigation for DIsability Applications) Project, funded and promoted by the Italian Space Agency (ASI) and implemented by Thales Alenia Space Italia with the collaboration of a mixed team of companies, university and user associations, has made concrete steps forward in demonstrating that satellite navigation applications can have an important role in facilitating the mobility of people with disabilities. This paper describes not only some basic features of the system, but looks at how they are related to the process of defining user needs and requirements, highlighting the role of end users and of professional users of Assistive Technology (AT).