SPACE APPLICATIONS OF THE GLOBAL POSITIONING AND TIMING SERVICE (GPtS)

Alison Brown, NAVSYS Corporation ABSTRACT Spaceborne Global Positioning System (GPS) technology is being widely accepted by both the commercial space industry and by NASA as a key enabler for improving space operations. The use of GPS for space missions has resulted in improvements in space vehicle autonomy and reduced design and operations cost. The current GPS constellation includes 24 MEO satellites with spares. These satellites are launched and operated by the US Air Force. GPS users also have access to signals from GPS augmentation systems. The first of these augmentation systems to transition to an operational capability is the FAA’s Wide Area Augmentation System (WAAS). Other organizations are actively developing augmentation services to GPS, and also developing follow-on satellite navigation capabilities. These include international variants of the WAAS service, planned for operation over Europe and the Pacific region, and new satellite navigation services, such as the proposed European Galileo satellite navigation constellation. The concept of a Global Positioning and Timing Service (GPtS) proposes a networked approach that provides enhanced global services using an integrated system-of-systems architecture, coupling signals -in-space from different sources. This places challenges in tightly synchronizing different networks of satellite constellations to provide seamless service coverage. GPtS applications for space users of the service include: autonomous orbit operations, accurate positioning and time synchronization, and attitude determination and accurate relative ranging between vehicles for formation flying. In this paper, some of the existing challenges for these applications are discussed and enhancements in GPS users’ equipment and in the evolving GPtS architecture are described that could benefit space applications.