This paper presents the preliminary study of a stratospheric segment within a satellite navigation system of present and future generation (GPS and Galileo) implemented by means of High Altitude and Very long Endurance (HAVE) platforms. The paper discusses a possible scenario in which the main features of the HAVE platform are exploited to define an innovative Aerial-Based Augmentation System (ABAS) for the provision of differential services. This particular local segment improves the provision of a differential navigation service. It is suited to the broadcasting of differential corrections in critical areas such as mountainous and sea regions where, to guarantee wide coverage, a large number of terrestrial reference stations would otherwise be required. The study includes a description of the proposed DGPS augmentation system, and a discussion of the system architecture and expected performance.