By Javier Benedicto
Head, Galileo Programme department,
European Space Agency
Javier Benedicto, left, accept the 2018 GPS World Satellites Leadership Award on behalf of Giuliano Gatti of the European Space Agency, from Phil Froom of Rockwell Collins. (Photo: Melanie Beus)
Since the Galileo initial services declaration in December 2016, the Galileo Program has been providing global PNT and search-and-rescue services for users worldwide. The European GNSS Agency (GSA) just issued its GNSS 2019 Market Report in October, providing a complete overview of the current status and trends of the GNSS worldwide market with focus on European GNSS (Galileo and EGNOS) applications and services.
In parallel with service provision, the Galileo Program is undertaking extensive infrastructure development and deployment activities to reach Full Operational Capability (FOC), incorporating new service capabilities, but above all aiming at increasing the robustness and resilience of the system infrastructure, operations and service provision.
Galileo’s signal-in-space quality has steadily improved over the past few years, reaching in 2019 a best signal-in-space error (SISE) of about 0.25 meters (95%, global average; Figure 1). This has been achieved through a combination of several factors, including the increased number of operational satellites, enhanced versions of the Ground Mission Segment, and higher uplink rate of the navigation message (lower age of data). This performance is well within Galileo’s initial service accuracy commitments, as defined in the public Open Service – Service Definition Document (OS SDD).
Figure 1. Long-term historical SISE plot over a 30-day sliding window, constellation averaged. (Image: ESA)
Figures 2 and 3 (see page 40) show Galileo’s timing performance as broadcast UTC offset and GGTO accuracy. The evaluation was performed with calibrated GPS/Galileo timing receivers operated in UTC(k) laboratory (PTB, INRIM). Again, the initial timing service commitments have been fully met.
Figure 2. Galileo Broadcast UTC offset accuracy performance. (Image: ESA)
Figure 3. Galileo GGTO offset accuracy performance. (Image: ESA)
Probably the most significant discriminator of Galileo compared to other GNSS is its capability to broadcast multi-frequency (E1, E6, E5) signal components on all operational satellites. The position performance of a dual-frequency user receiver on-ground is shown in Figure 4. This measurement from June 2019 demonstrates a Galileo position accuracy well below 2 m (95%).
Figure 4. Galileo position accuracy performance, dual-frequency, June 2019. (Image: ESA)
With the aim of further improving the Open Service (OS) performance, three newly introduced I/NAV message improvements on Galileo E1-B are under implementation, namely FEC2 Reed-Solomon Clock and Ephemeris (CED), Reduced CED, and Secondary Synchronization Pattern (SSP). Galileo Open Service (OS) users will benefit from improved robustness in terms of navigation data retrieval in challenging environments, in addition to facilitating a reduced time to first fix. Those I/NAV improvements on Galileo E1-B are backwards compatible with previously released OS SIS ICDs.
In addition, Galileo infrastructure is currently being upgraded to provide means for OS authentication. The protocol proposed uses the E1B External Data Broadcast Service (EDBS) to provide authentication data to the user. The OS Navigation Message Authentication (NMA) is based on an adaptation of the Timed Efficient Stream Loss-tolerant Authentication (TESLA) protocol.
Beyond the OS, the Galileo system has been designed to allow for the dissemination of value-added data, such as high accuracy and authentication, in the E6B signal component. The component has been designed to broadcast the Galileo High Accuracy Service based on the provision of accurate satellite data (clocks, orbits and biases) and atmospheric data (mainly ionospheric corrections) to enable multi-frequency multi-constellation PPP with correction data transmitted through an open format in the Galileo E6B signal.
The introduction in early 2020 of the automatic acknowledgment of the SAR/Galileo Return Link Message (RLM) as part of the Cospas-Sarsat system will enable space assets to be used for search and rescue — persons in distress will get swift acknowledgement that their alert has been detected and located. The Return Link is the means to interact with a SAR beacon, improving the effectiveness of SAR operations. Extensive testing has demonstrated that the median latency for the reception of a return link message on the ground is 14.2 seconds, while 99% of messages are received within 57 seconds, after the request for the RLM transmission is delivered to Galileo (from Cospas-Sarsat to the RLSP). At the same time, the measured rate of reception was 100%, considering line-of-sight availability, thanks to the very robust Galileo navigation data link. This performance has been demonstrated to be uniform across the globe, as shown in Figure 5.
Figure 5. Beacon activation map and RLM delivery latency through the Galileo system. (Image: ESA)
Following the re-profiling of the Galileo Safety-of-Life (SoL) service, Galileo is meant to be exploited through dual-frequency multi-constellation (DFMC) SBAS and will support the provision of integrity through the concept of Horizontal Advanced Receiver Autonomous Integrity Monitoring (H-ARAIM). To allow the exploitation of Galileo for these SoL applications, a thorough analysis of the actual signal-in-space (SiS) performance and of potential feared events critical for SoL users is key. In this context, the Galileo Integrity Failure Mode and Effect Analysis (IFMEA) process is implemented through measurements and review of the system design, including feared-events characterization.
Ground Segment Brings Robustness
Galileo telemetry and telecommand ground station. (Photo: ESA)
Galileo’s Ground Segment is being upgraded to fully redundant control centers. These include processing and storage, monitoring and control facilities, and security monitoring centers. A worldwide network of Galileo Sensor Stations (GSS) allows monitoring and measuring of satellite signals; uplink stations allow dissemination of the navigation message to users through Galileo satellites; and telemetry, tracking and control (TTC) stations allow monitoring and control of the satellites.
Ground segment upgrades under production by Thales Alenia Space France (in charge of the ground mission segment and security monitoring) and GMV Spain (in charge of the ground control segment) are addressing increased service robustness, through the introduction of a more flexible infrastructure with a significant technology refresh, improved security, service continuity, enhanced service performances, and enhanced operability features.
One important objective of the ongoing upgrades is to implement a modern infrastructure, based on leading virtualization technologies. This modernized infrastructure will make it possible to easily accommodate hardware and software changes without requiring significant redesign or requalification, and will minimize the impact to Galileo service operations — under responsibility of Spaceopal GmbH — during future deployment activities.
Batch 3, Ariane 6 Under Production
Ariane 6 on the launchpad. (Artist’s concept: ESA)
The production of Batch 3 of 12 additional Galileo FOC satellites is proceeding, aiming at readiness for launch by the end of 2020 onward. The satellite design includes a selected number of improvements compared to the 22 FOC satellites launched previously and built by the same satellite manufacturer OHB Systems.
The different stages of assembly, integration and initial test phase in the OHB production plant in Bremen have already started, before shipment to ESA-ESTEC in the Netherlands for the environmental test campaign consisting of thermal vacuum, mechanical tests, interface verification with the launcher and system end-to-end performance tests with the elements of the Galileo ground segment.
Following the phasing out of the Ariane 5 SE launcher, the third batch of Galileo satellites will be progressively launched with the new Ariane 62 launcher vehicle, the two solid-booster variant of Ariane 6 now in the final stages of development.
Evolution to Meet User Needs
The Galileo Second Generation roadmap has achieved maturity in 2019 and is now entering the preliminary design and implementation phase. Based on the EU’s H2020 Galileo Second Generation activities managed by ESA, and the GSA prospective market analysis, the European Commission, in close consultation with EU member states, has agreed on an ambitious set of long-term PNT goals for the future European GNSS infrastructures.
Technology pre-developments, critical engineering activities and synergic design activities between space and ground infrastructure are being conducted. This will translate into the progressive deployment of a complete set of space/ground infrastructure that is tailored to satisfy the diversified user needs in four main dimensions:
- Satellite and ground segment infrastructure with capabilities that can dynamically adapt to current and future user needs. Key drivers are flexibility and robustness, ensuring fast time to market to meet user needs.
- Full synergy between GNSS and SBAS systems infrastructure, to complement and enhance the service portfolio. This will allow segmentation and complementarity of safety-critical services and extension to all new PNT services available today, including high-accuracy positioning integrity.
- Enhanced integration with terrestrial systems — 5G/6G, signals of opportunity (SOOP), terrestrial beacon systems (TBS). ESA and GSA have been actively leading the 5G positioning standardization worldwide in collaboration with public and private institutions inside 3GPP and will soon move toward the start of standardization of 6G terrestrial positioning and GNSS interconnection technologies.
- Full complementarity with external sensors (such as INS, barometer and lidar) and application environments (low-power devices and internet of things) so that the Galileo Second Generation Infrastructure enhances and complements the capabilities provided by these external means.
A key pillar for this long-term strategy is the Galileo transition satellites. The competitive procurement procedure for the first batch of transition satellites is coming in 2020. The flexibility and robustness of these satellites will allow the European PNT infrastructure to satisfy all the different user needs in the next decade. This procurement — together with others at system, ground segment and technology level — will enable the start of the in-orbit validation of second-generation capabilities from 2025 onward.
Additional ground and test infrastructure are in early engineering analysis, design and technology development, in order to proceed with additional procurements for experimental and operational usage, starting early in the 2020s.