The Galileo Return Link Service Provider in Operation

Xavier Maufroid, Jesús Cegarra, Alicia Álvarez, Ignacio Moreno, Maxime Fontanier

Abstract:	The International Cospas-Sarsat Programme is a satellite based Search and Rescue (SAR) distress alert detection and information distribution system. Conceived as an international, humanitarian SAR system, it was constituted as an intergovernmental organization in 1988 by Canada, France, the USA and the former USSR (replaced by The Russian Federation in 1992). As of 2015, 42 countries participate in the operation and management of the System. The System is available to maritime and aviation users and to persons such a backcountry hikers in distress situations of all states on a non-discriminatory basis, and is free of charge for the end-user in distress. On average, about 5 persons are rescued every day with the assistance of the system. Galileo support to Search and Rescue service, herein SAR/Galileo, represents Europe’s contribution to the Cospas-Sarsat system, playing a key role of the Medium Earth Orbit Search and Rescue System, MEOSAR. The SAR/Galileo Service, with its Forward Link Alert Service is an integral part of the future MEOSAR system and ensures the detection and localization of the beacon distress signals through the relay of these signals by the Search and Rescue repeaters on board the Galileo satellites, their reception by the ground stations called MEOLUTs and alerts transmission to the Mission Control Centers. In addition, the SAR/Galileo Service will also introduce a new Search and Rescue function, called the Return Link Service (RLS), which provides acknowledgment messages to distress beacons equipped with a Galileo receiver, through the Galileo L1 signal. Galileo is currently the only GNSS system planning to provide this service worldwide. Provided by a dedicated facility called Return Link Service Provider, which will act as an interface between the Cospas-Sarsat and Galileo systems, the Return Link Service potentially enables various capabilities complementary to the existing ones. The European Commission has conducted a worldwide survey of the SAR community to consolidate the definition of the proposed RLS, which currently consists in the Acknowledgement Service to confirm the detection and localization of the alert to the distress beacon. This acknowledgment is fully automatic and the Galileo system autonomously transmits via the RLSP a Return Link Message to the emitting beacon after the alert has been detected and located and the Return Link Message (RLM) request has been received by the FMCC. Within the Galileo system, the Return Link Service Provider, RLSP, is the facility in charge of the formation of the Return Link Messages and their coordination with the Galileo system, interfacing on one side with the Cospas-Sarsat network and on the other side with the Galileo Ground Mission Segment (GMS) for the transmission of RLMs to the distress beacons through the Galileo L1 signal. The main functions of the RLSP are summarized below: • Autonomous management of the RLM (system automatic acknowledgment), being the RLSP uniquely responsible for the transmission of a Return Link Message (RLM) to the emitting beacon once the RLM request has been received and once the location of the alert has been confirmed by the Cospas-Sarsat; • Ensure operations on 7d/24h basis. • Operate specific on-line interfaces to: o Receive RLM requests from the French Mission Control Centre (FMCC); o Deliver RLM requests to the GMS and exchange auxiliary data with it; o Prepare a prioritized list of satellites for the dissemination of the RLM depending upon the localization of the distress beacon. The RLSP facility will be installed in the SAR/Galileo Service Centre in CNES, Toulouse where the Cospas-Sarsat French Mission Control Centre (FMCC) is also operated. Also CNES will be responsible for the operation of the RLSP along with the coordination of the overall SAR/Galileo Ground Segment operations. The activities for the development of the RLSP V1 were officially launched on September 15th, 2016. The solution envisaged takes care of the design drivers, paying special attention to aspects such as the interfaces, security, expected expandability to cover additional services, satellites and users, the demanding availability and long term maintainability requirements, the intended operation or the generation of quantitative key performance indicators. The first operational version is working from the beginning of 2020 providing this service to all the users with a beacon Galileo compatible. The operator from CNES premises are able to manage the messages coming from the beacons and sent RLMs to the satellites through the Galileo Mission Segment. The operators are able to change different algorithms parameters in order to selected different satellites for the uplink, elevation angle or set the time for the acknowledgement repetitions. They are able, also, to see in the map all the beacons that have sent an alert message and the status of their RLM such a In Progress, Pending, Disseminated or Terminated. In this paper, the authors present will present an analysis of the results of the first months of operation of the system, analyzing the number of beacons processed during the period of analysis, satellites used for the uplink, total number of repetitions per beacon, mean time of dissemination, standard deviation time of dissemination or the worldwide coverage of the service. The results will provide to the audience a very interesting first vision of the performances of this innovative service provided for the first time in the world.
Published in:	Proceedings of the 33rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2020) September 21 - 25, 2020
Pages:	856 - 883
Cite this article:	Maufroid, Xavier, Cegarra, Jesús, Álvarez, Alicia, Moreno, Ignacio, Fontanier, Maxime, "The Galileo Return Link Service Provider in Operation," Proceedings of the 33rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2020), September 2020, pp. 856-883. https://doi.org/10.33012/2020.17729
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