Enhancing GNSS with a Low Earth Orbit layer: Celeste In-Orbit Demonstration Mission

Global Navigation Satellite Systems (GNSS) are the backbone of worldwide Positioning, Navigation, and Timing (PNT) services, but their performance and availability are challenged in demanding environments such as urban canyons or under natural or man-made threats such as jamming and spoofing. The European Space Agency’s Celeste In-Orbit Demonstration (IOD) mission aims to demonstrate the capabilities of Low Earth Orbit Positioning Navigation and Timing (LEO-PNT) systems to increase resilience, augment and complement existing GNSS and provide additional services. This in-orbit service demonstration addresses limitations and vulnerabilities by leveraging the unique characteristics of LEO satellites—such as fast geometry changes and reduced propagation losses—to complement GNSS. The mission will validate frequency diversity through PNT signal transmission in multiple bands (L, S, C, UHF), demonstrate onboard Orbit Determination and Time Synchronisation (ODTS), and broadcast 5G NTN signals to provide enhanced positioning capabilities. Celeste IOD is implemented through two parallel industrial contracts, each encompassing the development of a mini constellation with satellites with different payload capabilities, ground and user segments, launch services, operations and comprehensive experimentation and service demonstration campaigns. Pathfinder A satellites will validate core technologies and L/S-band payloads, while Pathfinder B satellites will expand capabilities to other bands like C-band, UHF, other capabilities like two-way or integrity monitoring, and multi-satellite service demonstrations. By providing critical performance data, validating new signal configurations, and engaging end-user communities, the Celeste IOD mission will pave the way for a robust, multi-layered European PNT architecture, augmenting Galileo and EGNOS, and supporting public safety, commercial innovation, and European leadership in satellite navigation. The evolution of PNT systems toward a multi-layer, multi-orbit architecture—combining MEO GNSS, LEO-PNT, and terrestrial networks—represents a fundamental shift in the field. This shift is being driven by both public and private stakeholders, and is the subject of active research, standardization, and demonstration worldwide. The Celeste IOD mission is a key step in this evolution, providing critical data and experience to inform the future of resilient, high-performance PNT.