LIFELINE: Feasibility Study of Space-Based Relativistic Positioning System

Abstract

All GNSS in operation are based on Newtonian physics and rely on global reference frames fixed to Earth. Relativistic effects are treated as deviations. Precision and stability in time of the reference frames is provided via ground stations and their final accuracy is limited by the Earth´s dynamics and atmosphere. Several theoretical concepts have been proposed in the past for the use of Relativistic Positioning Systems (RPS) and the required relativistic reference frames with different approaches and the consistency with the General Relativity (GR) has been demonstrated. However, none of the previous works brought forward the theoretical framework into the consequences of a practical implementation. Passing from these to actually implementable systems requires engineering of the required concepts, numerical tools and technology, and implementation of the consequences in the final system design, architecture, performance and operations. The main objective of this work is to provide an early design of a Relativistic PNT System, analyse its feasibility, identify its required architecture and its technological enablers. In the paper, a brief state-of-the-art review of RPS literature and potential identified Use Cases is provided, which allows to define a set of Mission Requirements for RPS. Different potential System Concepts for RPS are identified and the Practical Exploitation of RPS theoretical concepts is explored. An Architecture for RPS is selected based on the previous trade-off and described, together with the technological elements for the practical realization, including: • Inter-satellite links for the interchange of General Relativity coordinates between satellites in order to build an autolocating RPS, • Enhanced on-board clocks with performance in line with the target accuracy of the orbits determination, • Elements for processing of additional information. Autonomous RPS, in addition to the auto-located RPS information exchanged between satellites via Inter-satellite Links, would be completed with: o Dynamical data of the SVs (acceleration and/or gradiometry), o Observational data from SVs (position of the reference quasars, terrestrial stations), o Gravitational knowledge of the emission coordinates region. • Multi-layer constellation Finally, the RPS concept is tested using a tool with RPS Algorithms implemented. A feasibility analysis of the recommended option is performed based on simulations for determining the performances and assessing the benefits of the RPS proposed design.