GNSS Augmentation Satellite System (GAUSS)
Thomas Zechel, Omar Garcia-Crespillo, Grzergorz Michalak, Matthias Simon, Tobias D. Schmidt, Gabriele Giorgi, German Aerospace Center – Institute of Communications and Navigation; Michael Meurer, DRL & RWTH Aachen University, Chair of Navigation; Jean-Jacques Wasbauer, Clément Gazzino, Francois Dufour, Alexandre Ramos, Centre National d'Etudes Spatiales
Date/Time: Friday, Sep. 20, 2:12 p.m.
Global Navigation Satellite Systems (GNSS) have become an indispensable part of modern society, and will become even more so in the coming years. The market of positioning, navigation and time (PNT) services is fast growing as a multiplicity of user groups are already relying on those services and new user groups are discovering the advantages of PNT services based on GNSS. The field of applications is large ranging for instance from financial transactions, climate change research, synchronization of critical infrastructure such as power grid networks, up to (autonomous) driving, flying of unmanned and manned vehicles to only name a few areas. However, latest advances in GNSS and the exploitation of new user groups are accompanied by more demanding requirements for the existing GNSS constellations in particular with respect to autonomy, robustness, accuracy, precision and integrity. This holds especially true for safety-of-life-services. Unfortunately, currently available systems are limited in performance and cannot meet the high demands and requirements needed for such future applications. Thus, new technologies, concepts and architectures are needed. The German Aerospace Center (DLR) already proposed a new GNSS architecture called Kepler which incorporates optical technologies in particular for inter-satellite links in MEO (medium earth orbit) for synchronization and ranging purposes in order to achieve instantaneous globally available high accuracy in combination with high robustness and autonomy. In addition, globally available high integrity is achieved in KEPLER by complementing the classical MEO GNSS constellation by a set of smaller satellites flying in LEO (low earth orbit). This LEO layer has, beside others, the functionality to monitor the broadcasted signals of the MEO GNSS satellites in space with low or no degradation due to ionospheric or tropospheric delay as well as multipath. The goal for the LEO layer is to detect anomalies, contribute to precise orbit determination (POD) in space, support the identification and estimation of signal and system biases as well as to provide a global integrity service without the need of deploying a global network of monitoring ground stations. Although this LEO layer has originally been proposed as part of the KEPLER system architecture, this monitoring layer is not limited to KEPLER but is also of high interest for providing monitoring and integrity functionalities for existing GNSS like GPS and Galileo. While the optical technologies for the implementation into future (MEO) GNSS are currently developed and are being prepared for in-orbit validation within DLR’s COMPASSO project, the development of the conceptual functionalities of the LEO layer was started in a separate project/mission called GAUSS (GNSS Augmentation Satellite System). GAUSS is a joint project between the Centre national d'études spatiales (CNES) of France and DLR. It can be divided into two parts:
1. Development of the global space enabled augmentation concept.
2. Planning and execution of an in-orbit Demonstration Mission for key technologies and core concepts.
This submission will present an overview of the envisioned global concept. The goal for the global augmentation concept is to create a satellite system that consists of small satellites in LEO that monitors the existing GNS Systems (GALILEO and GPS) and provides a global integrity overlay mainly for GALILEO and GPS. The key requirements on the system to achieve these goals are:
- Precise orbit determination of the LEO satellite orbits that will function as the monitoring stations in space using the broadcasted GNSS signals as well as auxiliary measurements;
- extended monitoring capabilities onboard the LEO satellites to monitor the navigation signals from selected MEO constellations (multi-frequency, multi-constellation);
- Monitoring of and integrity services for Galileo’s high accuracy service (HAS);
- Contribution to the precise determination of the MEO orbits;
- Analysis of the gathered data for anomalies and feared events;
- Identifying threats;
- Provision of error bounding as well as raising flags in case of integrity threshold value violations.
Following the aforementioned approach GAUSS will be able to provide a powerful integrity augmentation as well as corrections for the tracked GNSS constellations which can be disseminated to the users.
The advantages of the envisioned GAUSS concept are the global coverage that can already be achieved by a small number of monitoring stations in low earth orbit. The implementation of the concept in currently planned constellations is emphasized. The paper will give an overview over this novel space enabled integrity scheme, will present some major design trade-offs of such a system as well as will discuss most important benefits and challenges linked to this novel concept.
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