RTOD: A Real-time Precise Orbit & Clock Determination System

The development of a Real-Time precise Orbit & clock Determination system (RTOD) is presented in this paper. The main objective of the RTOD programme was to provide a future-proof global GNSS augmentation facility capable of driving a real-time Precise Point Positioning system with a target accuracy approaching one decimetre (RMS), or better. The RTOD system was developed by Thales Research & Technology (UK) Ltd (TRT), in liaison with the British National Space Centre (BNSC), the National Physics Laboratory (NPL), the UK Meteorological Office, Thales Positioning Ltd and Thales Air Traffic Management Ltd. The RTOD system provides highly accurate GNSS satellite orbit trajectories and clock correction parameters in real-time. The system utilises a fully in-house design and implementation that is easily extensible to future GNSS systems such as Galileo or modernised GPS. The main objectives of the paper are twofold. Firstly to present a description of the system and the design principles underpinning it, and secondly to describe its performance. The paper firstly provides an overview of the RTOD system itself, including descriptions of the key sub-system architecture and functionality, as well as details of key system operating configurations. The flexibility of the overall system architecture is illustrated through the presentation of two, very different, example GNSS service applications, both driven by the RTOD system. The paper continues with the presentation of results of an evaluation of the RTOD system, together with the example GNSS service applications, utilising GPS and NWP data for a global network of thirty-six tracking stations. The paper will demonstrate 3-D orbit accuracies commensurate with that required for a decimetre level positioning system. The paper will further demonstrate a real-time PPP accuracy approaching that obtained using the latest commercially available services achieved using the RTOD-based RTCM Message service. The paper concludes with suggestions for further enhancements in the RTOD system and possible avenues of exploitation that would capitalise on the extensive work carried out so far.