Europe’s Galileo navigation system has taken a significant leap forward with the completion of a major upgrade to its Galileo Ground Segment. As one of the most complex ground segments ever developed in Europe, the challenge lay in seamlessly upgrading a system that serves more than four billion users globally—without disrupting service.
The result is an enhanced infrastructure that drives Galileo toward full operational capability while securing Europe’s position as a leader in satellite navigation.
With 32 satellites orbiting Earth after the system’s thirteenth successful launch, Galileo, which has been operational since 2016, delivers meter-level accuracy to users worldwide. At the core of this system is the Galileo Ground Segment, developed and maintained by a collaboration of top European aerospace entities: the European Space Agency (ESA), Thales Alenia Space, Spaceopal (DLR GfR and Telespazio), the European Commission (EC) and the European Union Agency for the Space Programme (EUSPA).
The Galileo Ground Segment is a vast and intricate system comprising:
• Two Galileo Control Centres (GCC) located in Italy (GCC-I) and Germany (GCC-D), ensuring redundancy.
• Two Galileo Security Monitoring Centres (GSMC) based in Spain (GSMC-E) and France (GSMC-F).
• A global network of uplink (ULS) and sensor stations (GSS).
• The Galileo Data Dissemination Network (GDDN), a dedicated network, controlled and managed end-to-end by the Galileo program (no dependency on the internet) and which gives continuous availability.
• Seven External Entities (EE), including the Galileo Service Centre (GSC) for service monitoring and the Return Link Service Provider (RLSP), which supports Galileo’s Search and Rescue (SAR) service, connected via the External Data Distribution Network (EDDN).
On March 11 at 13:39 UTC, Galileo satellites started transmitting the first navigation message from the newly upgraded Ground Segment System Build 2.0 (SB 2.0). This landmark event heralded several critical improvements that not only enhanced current operations but also laid the groundwork for future Galileo architectures, such as the upcoming Galileo Second Generation’s.
Key features of the SB 2.0 upgrade include:
• Modernized Ground Mission Segment (GMS) infrastructure with enhanced resilience.
• Enhanced Public Regulated Service (PRS).
• Strengthened security monitoring via the Security Operations Centre at the Galileo Security Monitoring Centres.
• Upgraded cybersecurity protections.
• Preparations for future developments, including the transition to Galileo Second Generation.
The migration of the Ground Segment to SB 2.0 was achieved without disruption to Galileo’s vast user base, thanks to meticulous planning based on lessons learned from previous upgrades, particularly the Ground Mission Segment update in 2019. This article dives deeper into the specifics of how this intricate and challenging upgrade was accomplished.
Ensuring Seamless Operation: The Upgrade Strategy
A system relied upon by four billion users every day cannot afford any significant downtime. To avoid this, the upgrade strategy for Galileo’s Ground Segment was carefully crafted and executed through six distinct phases.
Phase 1: Upgrade approach and design
The initial step in upgrading the GMS infrastructure involved designing an effective and robust migration strategy while adhering to key constraints outlined by Galileo stakeholders:
• Maintain business continuity throughout the migration process.
• Avoid introducing any single points of failure.
• Validate all intermediate system configurations.
• Rehearse all upgrade steps.
• Ensure rollback capability at every stage of the upgrade.
To meet these stringent requirements, the concept of a pre-operational (pre-OPE) chain was introduced as the upgrade solution. The pre-OPE chain is a fully redundant and upgraded GMS Core infrastructure, incorporating both GCCs and GSMCs, updated to ground segment version 3 (V3). Meanwhile, the existing operational (OPE) chain, based on version 2 (V2), remained isolated. This approach offered several advantages over previous migration strategies:
• Continuous chain redundancy throughout the deployment and upgrade.
• Simplified upgrade steps.
• Shortened overall upgrade duration.
• Flexible scheduling of upgrade activities without inter-chain constraints.
• Easier and more efficient rollback procedures.
During this phase, the migration team developed a comprehensive plan, covering design adjustments, validation methods, and the steps for migration and accreditation.
Phase 2: Deployment and validation of pre-operational chain
In the nominal setup, each Galileo Center is equipped with:
• An OPE chain managing operations to the spacecrafts and delivering real-time service to the users via the network of worldwide antennas.
• A validation (VAL) chain used for validation of new features, troubleshooting and operator training purposes. The VAL chain is not connected to any of the antennas worldwide, however, it gets the observables forwarded from the OPE chain.
A dedicated pre-OPE space was established in the two GCCs and the two GSMCs. More than 90 components were either newly deployed or upgraded during this phase, involving more than 400 individual installations, a process that spanned 2.5 years. On the other hand, two of the four VAL chains were updated to V3 in GCC-D and GSMC-E.
After completing the deployment of the pre-OPE chain to each site, the pre-OPE chains were interconnected, but always fully segregated from the OPE chains, to not interfere with the service provision. Further, as for the VAL chain, the pre-OPE chains got all the data from the antennas worldwide without being connected to them.
This parallel deployment allowed both OPE and pre-OPE systems to operate side by side to:
• Train operational personnel on new functions brought by ground segment V3 as well as verifying team readiness on routine operations.
• Verify pre-OPE robustness in the targeted real-time operational environment.
• Demonstrate that pre-OPE delivers a navigation message performance in line with the demanding requirements in terms of orbitography and clock synchronization.
In such a complex system of sub-systems, an extensive configuration and tuning effort of several weeks was unavoidable to determine and baseline the final working point of the chain. A final validation campaign allowed to state the readiness of the pre-OPE, demonstrating it is ready to deliver service.
Phase 3: Rehearsal of the migration
Phase 3 focused on rehearsing the migration with the objective to establish and validate the operational procedures achieving a seamless service transition from V2 to V3 and demonstrating rollback capabilities that can be triggered at any point during the migration execution to guarantee the service alive. These operational procedures contain actions such as disconnecting or connecting cables, moving critical equipment and aligning operational context between OPE and pre-OPE.
The rehearsal phase spanned seven months, by testing first isolated sequences and then putting together all the pieces of the puzzle to achieve the overall migration sequence.
To avoid jeopardizing the service provisioning from the OPE chain, it was not possible to test the transition from the V2 OPE chain to the V3 pre-OPE chain during the rehearsal. Consequently, this transition was rehearsed by connecting the VAL chain (still in V2) to the pre-OPE chain, simulating the transition from V2 to V3.
The original plan was to execute migration for the four control centers in one day. However, the rehearsal phase revealed this approach carried significant risk on the service provision, as many critical activities would need to be performed successfully in a truly brief time, leaving little margin for troubleshooting if issues arose.
During these early runs, unpredictable technical issues surfaced, making it clear the plan to migrate all four chains in one day was too optimistic. The compressed timeline offered little flexibility to address unexpected problems. Consequently, if troubleshooting could not resolve an issue quickly, the entire migration would need to be rolled back, and the process would have to start again from the beginning.
Change of Strategy
After evaluating the challenges faced during the first rehearsal runs, the migration strategy was optimized. Instead of migrating all four chains simultaneously, the team designed a phased approach. First, one GCC V3 would be integrated into the new system. Once the integration was completed, the service would be transferred from one GCC V2 operational chain to the new integrated GCC V3 chain.
After the successful migration of one GCC, the second GCC would undergo the same pre-integration, and only then would a nominal handover be conducted to complete the migration for both GCCs. Following the migration of the two GCCs, the two GSMCs would be migrated.
This new phased strategy significantly reduced the risks associated with the transition and allowed the team to better manage potential issues that might arise during the process.
Final Rehearsal Runs proved the feasibility and effectiveness of the final operational procedures and team readiness, demonstrating the Galileo system could transit smoothly from V2 to V3 without Open Service disruption.
A multitude of technical details was sorted out and several degraded cases could be addressed to push the system to its limits.
Finally, the only missing piece of the puzzle was to ensure the remote sites (i.e. ULS and GSS) could be successfully integrated in the new V3 pre-OPE chain. As explained earlier, the remote sites are only nominally connected to the OPE chain, and the data is then forwarded to the VAL/pre-OPE chain so the VAL or pre-OPE chain does not accidently interfere with the OPE chain’s service provision. After careful planning, one antenna was disconnected from the OPE chain and connected to the pre-OPE chain before the actual migration, verifying the proper integration, i.e. commandability and monitoring capabilities of this antenna from the pre-OPE chain.
After the successful integration of this antenna on the pre-OPE chain, the antenna was re-integrated on the V2 OPE chain. With this, the migration team was confident and enthusiastic to enter the next phase.
Phase 4: Migration of the GCCs
The migration process began on March 4, with the integration of the GCC Germany V3 chain into the operational environment. This involved disconnecting all the remote sites and external entities connected to the Galileo network from the V2 chain in Germany and reconnecting them to the V3 chain, while Italy’s V2 chain continued to provide service.
Throughout the week, more than 50 remote elements were systematically integrated into the GMS V3 at GCC Germany, ensuring each component was properly connected and fully functional. A final alignment of operational contexts between OPE and pre-OPE was executed, ensuring perfectly mirrored chains. The planning context, which included the allocation of ULS antenna contacts to satellites, was one of the alignment items, ensuring a seamless transition from OPE to pre-OPE for the ULS antenna.
During the weekend, after this initial integration, the team continued to carefully monitor the stability of the system and perform routine operations.
On Monday, March 11, the critical service transfer from the GCC Italy V2 chain to the GCC Germany V3 chain took place. The operation commenced at 07:00 CET with more than 200 personnel stationed across all Galileo sites and external entities. Several key actions were undertaken, starting with the
handover of commanding of all ULS and GSS antennas, one by one, from GCC Italy V2 to GCC Germany V3. During that step, real-time mission data was still disseminated from GCC Italy V2.
Subsequent checks of synchronization took place to confirm time references of both OPE and pre-OPE were aligned to within a tenth of a nanosecond. Such a synchronization is critical, as it guarantees the change of the navigation message from OPE and pre-OPE will have a negligible impact for users.
At 13:39 UTC, real-time mission data dissemination was activated. The first Galileo navigation message was uplinked from the new GMS V3, marking a pivotal moment in the migration process. Throughout the day, teams continued fine-tuning the system and in parallel still operated the legacy GMS V2 version to maintain rollback capabilities in case a critical issue would have occurred on GMS V3. At the end of the day, the GMS V3 chain was operating smoothly, with all Galileo services (OS, HAS, OSNMA, SAR return-link) working nominally. It was an intense, exhausting, but remarkable day for the teams. The pressure was immense, but the months of rehearsals and the strength of the plan proved their worth.
As seen in Figures 7, 8 and 9, Galileo system performance remained excellent and neither a change in the Signal In Space Ranging Error (SISRE) nor a jump on the Galileo System Time (GST) was observed when switching from GMS V2 to V3.
The following day, March 12, the GCS was successfully integrated with the GMS V3. The migration campaign was strategically planned so the critical migration activities would occur on Monday and Tuesday, leaving ample time to address non-critical issues by the week’s end. The entire system was closely monitored until the end of the week and over the weekend to ensure stability.
In the subsequent week, beginning on Monday, March 18, a similar process was conducted at the GCC Italy site. As in Germany, all remote sites and external entities connected to the Galileo network were disconnected from the V2 chain in Italy and connected to the V3 chain, while the Germany V3 chain continued providing service.
The migration of the GCCs concluded with a smooth handover of operations from GCC Germany back to GCC Italy, completing the transition. Throughout the migration, there was no disruption to Open Service users, and the Galileo signal’s stability remained exceptional.
Phase 5: Migration of the GSMCs
Following a period of system stabilization, attention turned to the GSMCs. The migration scenario was strategically designed so the GMS upgrade was executed first, followed by the GSMC upgrade. This approach ensured the overall system could be migrated in a controlled and coordinated manner while still offering rollback capabilities in case of any issues. At the start of Phase 5, the legacy GSMC version remained connected to the new GMS. During this phase, the GSMC was upgraded to version V3.
Phase 6: Upgrade of the worldwide uplink and sensor stations
With the critical upgrades to the GCCs and GSMCs completed, the final phase involved upgrading the worldwide network of uplink and sensor stations.
In May, starting with the GSS in Redu, Belgium, a site quick and easy to access, was chosen to demonstrate the feasibility and allow—if needed—for easy troubleshooting and potential re-visit of the site.
After the successful upgrade of the Redu station, the next upgrade took place on the remote island of La Réunion, a combined Galileo site that supports GSS, ULS and Telemetry and Tracking Stations (TTC). Over six weeks, more than 20 personnel were stationed on site, with additional support from the GCCs and GSMCs in Europe. The sheer complexity of this operation was amplified by the remote nature of Réunion itself, which lies more than 9,000 kilometers away from the ESA’s headquarters in Europe. One of the most significant challenges in Réunion was ensuring all involved parties were synchronized in their efforts. This upgrade required the temporary removal of critical operational assets from service, necessitating tight coordination to prevent any disruptions to Galileo’s global operations.
With Réunion fully upgraded, the focus shifted to the Jan Mayen site in the Arctic Ocean, which was completed in August and will be followed by the other remaining remote sites.
Conclusion
The completion of the SB 2.0 migration represents a remarkable achievement for Europe’s Galileo navigation system. Culminating years of preparation, the upgrade was executed seamlessly over a six-week period, involving more than 200 personnel spread across Europe. This success not only bolsters Europe’s capabilities in satellite navigation but also supports key policy objectives in security, defence, resilience, and global competitiveness.
The new Galileo Ground Segment is now more robust, secure and prepared for the future, ensuring the system continues to provide precision and reliability to its billions of users worldwide.
Acknowledgements
The successful migration to SB 2.0 marks a significant milestone made possible by the dedication, talent and collaboration of an exceptional team. This achievement reflects the commitment and hard work of each individual involved, and the authors would like to extend their sincere gratitude to all contributors.
We would especially like to thank the European Commission (EC), the EU Agency for the Space Programme (EUSPA), the Security Accreditation Board (SAB) with the support of Member States and the Security Accreditation Department (SADEP), Spaceopal—the main contractor for operational services—as well as all other experts within the European Space Agency and Thales Alenia Space. Your dedication has not only transformed what is possible but will also have a lasting impact on the future of Galileo. Thank you for your outstanding contributions in bringing SB 2.0 to life.
Authors
Miguel Manteiga Bautista is the Galileo program manager, inside the Directorate of Navigation of the European Space Agency. He obtained his MSc degree in 1999 in telecommunications engineering from the University of Valencia, Spain. In 2005, he obtained an International Executive Master in Business Administration from the IE Business School.
After spending his early career developing and deploying high-speed telecommunication networks in Telefonica SA, he moved to the ESA Galileo Team in 2001. Throughout the last 23 years, he has developed his career in the Galileo program in various positions covering all areas of the Galileo environment (space, ground, user, launcher, system, security, operations, project and program management).
In 2015, he took over the position of head of GNSS/Galileo Evolution program, he became Galileo Second Generation Project Manager in July 2020 and has been head of Galileo Programme Office since 2024. He is responsible for the overall program-level implementation of Galileo activities at ESA, in close coordination with the European Commission and European GNSS Agency representatives.
Sonia Toribio holds a master’s degree in computer science from the Universidad Politecnica in Madrid (1999), a master’s degree in system engineering from the Ecole Nationale Supérieure des Télécommunications in Paris (2001) and a master’s degree in Space Systems and Business Engineering from the Delft University of Technology (2011). She has worked on the Galileo Ground Segment over the last 23 years, first in industry and then as part of the Galileo team at ESA.
She has been involved in several areas within the Ground Segment procurement, starting with studies during Phase B back in 2003, then being responsible for the procurement of the Ground Control Segment (GCS) of the Giove A and Giove B satellites (Galileo In Orbit Demonstrators) as well as the In Orbit Validation (IOV) and Full Operational Capability (FOC) Phases.
In 2013, Toribio was appointed as ESA Galileo Ground Control Segment (GCS) Project Manager. In 2020, Sonia was appointed as ESA Galileo Ground Mission Segment (GMS) and Ground Segment Security Project Manager, responsible for the procurement, qualification and delivery of the System Build 2.0 (Public Regulated Service Initial Operational Capability) and the upgrade of the most complex Ground Segment ever built in Europe, which was completed in April 2024.
In 2024, she was appointed as ESA Galileo Ground Segment manager responsible for evolutions of the GCS, GMS and Ground Segment security infrastructure.
Sven Richter holds a master’s degree in computer science from the University of the Federal Armed Forces in Munich, which he completed in 2002. He commenced his professional journey by contributing to the development of safety-critical real-time systems for both the German Military and NATO.
Transitioning to the space industry, he joined the European Space Agency (ESA) in 2010, where he served as an engineer specializing in on-board software for the Solar Orbiter and Sentinel 2 project. In 2016, Richter joined the Galileo project at ESA. Here, he specialized in deployment, integration and verification. He has overseen the Galileo Ground Mission Segment’s deployment activities since 2022.
Anas Tajdine holds a Ph.D. in applied mathematics from the Universidad Complutense of Madrid. He has been involved in European navigation programs development over the last 23 years. He joined Thales Alenia Space in 2013. He has been GMS Performance Manager, Design and Development Manager and WP2x technical manager. He is currently GNSS ground chief engineer for Thales Alenia Space, acting as program design authority and ensuring segment technical coordination.
Vincent Borrel holds a master’s degree in communications engineering from IMT Atlantique engineering school in Brest, which he completed in 2004. He first worked in DLR in Munich in satellite communications studies. He has been involved in the Galileo program since 2005 for Thales Alenia Space, first working on Galileo ground segment algorithms. He then was seconded in ESTEC in 2014 and 2015 on end-to-end system validation, where he was actively involved in the early phases of the Galileo system integration activities, such as first position fix validation. He was then responsible for Galileo PRS service exploitation for Thales Alenia Space and is now technical manager of Galileo Ground Segment migration.
