Directions 2021: Galileo expands and modernizes global PNT

Authors Javier Benedicto (ESA), left, and Rodrigo da Costa (GSA). (Image: ESA)

Throughout 2020, the Galileo Programme under the responsibility of the European Commission, the European GNSS Agency (GSA) and the European Space Agency (ESA), has been delivering continuous and reliable global PNT and Search and Rescue (SAR) services, developed improvements to Galileo First Generation ground and space system infrastructure for increased robustness and new service capabilities, and launched a full modernization program aiming in the future at Galileo Second Generation.

The GNSS User Technology Report 2020 has just been released by GSA, providing a complete overview of the current status and trends of the GNSS worldwide market with focus on user technology and in particular European GNSS (Galileo and EGNOS) applications and services.

In addition to providing a high quality open service based on innovative signals in the E1 and E5 bands, Galileo is also the first GNSS constellation to comprise a SAR capability, including the provision of a return link to users in distress. Galileo also features unique capabilities, such as the provision of Navigation Message Authentication (OS-NMA) and of an encrypted navigation signal on E6, the Commercial Authentication Service (CAS). These functions will offer the first protection against spoofing available to civilian GNSS users.

Finally, Galileo will provide free access to a High Accuracy Service (HAS) through the use of an open data channel used to broadcast high-accuracy augmentation messages.

Performance Meeting Expectations

The Galileo constellation consists today of 22 operational spacecraft (24 satellites are available for the Search and Rescue service). Two additional satellites (GSAT0201/E18 and GSAT0202/E14) are currently under testing with regard to potential operational as auxiliary usage in the near future.

The long-term evolution of performance parameters reveals that the Galileo system is continuously improving. In particular, an excellent quality of the navigation message in terms of ranging accuracy can be observed. Since the Initial Service declaration in 2016, ranging accuracy has steadily improved reaching a level of ~25 cm (95%) by mid of 2020, see Figure 1.

FIGURE 1. F/NAV SISE as observed by user receivers (constellation average, 30 days moving average). (Image: ESA)

The timing accuracy benefits from the larger number of satellites in service. Figures 2 and 3 present the evolution of the UTC dissemination accuracy and GGTO accuracy performance better than 2.5 nsec and 4.2 nsec (95%) respectively, which are largely within Galileo service commitments.

Figure 2. UTC dissemination accuracy. (Image: ESA)

Figure 3. GGTO accuracy. (Image: ESA)

Probably the most significant discriminator of Galileo versus other GNSS is its capability to broadcast multi-frequency (E1, E6, E5) signal components on all operational satellites. In the high-end and mid-range smartphone chipset market, dual frequency is becoming the norm. All large players have released dual-frequency chipsets, and the first dual-frequency chipsets targeting the budget device market are now becoming available. Dual-frequency receivers offer improved accuracy and robustness, and potential access to high-accuracy techniques. Multi-constellation is now standard for high-volume chipsets and Galileo with its multi-frequency capability is one of the largest GNSS contributors to this emerging dual-frequency PNT market.

Expanding Galileo Services Portfolio

Galileo offers the Galileo Open service (OS) for positioning and timing services, and Europe’s Search and Rescue (SAR) service contribution to COSPAS-SARSAT, equipped with its unique Return Link Message (RLM) declared operational in January 2020. Furthermore, the Galileo system is expanding its infrastructure capabilities such that, once fully operational, it will offer additional high-performance services worldwide.

Public Regulated Service (PRS) is restricted to government-authorized users for sensitive applications that require a high level of service continuity.

Open Service INAV message improvements on Galileo E1-B are under implementation, namely robust symbol level synchronization patterns, additional insertion of clock and ephemeris data with flexible outer encoding and frequent provision of shortened clock and ephemeris for improved robustness in terms of navigation data retrieval in challenging environments, in addition to facilitating a reduced time to first six (TTFF); these improvements ensure backwards compatibility with previously released OS SIS ICDs.

Open Service Navigation Message Authentication (OS-NMA) providing the free authentication of the Galileo Open Service (OS) for geolocation information through the Navigation Message (I/NAV) broadcast on the E1-B signal component.

Commercial Authentication Service (CAS), complementing the OS, providing a ranging authentication function implemented by encrypting the spreading code of the E6C (pilot) channel with a secret key. To ensure backward compatibility, CAS is based on the only civilian signal including cryptographic features (E6). When using both OS-NMA and CAS, users will benefit from data (navigation message) and range authentication, allowing PVT authentication worldwide.

Galileo Batch 3 satellite under test at ESA’s ESTEC facility in the Netherlands. (Photo: ESA)

High Accuracy Service (HAS) complementing the OS by delivering free access high accuracy data and providing better ranging accuracy, enabling users to achieve sub-meter level positioning accuracy.

Support to Safety of Life (SoL) Services through Dual Frequency Multi-Constellation (DFMC) SBAS and supporting the provision of integrity through the concept of Horizontal Advanced Receiver Autonomous Integrity Monitoring (H-ARAIM). In this context, the Galileo Integrity Failure Mode and Effect Analysis (IFMEA) Process is implemented through measurements and review of the system design, including characterization of feared events.

Galileo Batch 3 satellite under test at ESA’s ESTEC facility in the Netherlands. (Photo: ESA)

Infrastructure Modernization

The Galileo System infrastructure is being upgraded and modernized to support the full service portfolio, provide additional robustness and resilience, ensure security and improve operations.

The Galileo Ground Segment is being upgraded implementing ground segment virtualization technologies. This modernized infrastructure will make it possible to easily accommodate technology refresh and will minimize impact to Galileo service operations, under the responsibility of Spaceopal GmbH, during future deployment activities.

Current ground segment upgrades under production by prime contractor Thales Alenia Space in France (in charge of Ground Mission Segment and Security Monitoring) are addressing the deployment of improved robustness of the navigation and precise timing solutions, the full scope of PRS service capabilities, the expansion of the sensor station and up-link ground station networks, and additional security monitoring coverage to protect Galileo ground and space assets.

Ground segment upgrades under production by prime contractor GMV in Spain are addressing the deployment of a new Ground Control Segment providing increased constellation monitoring and control capabilities up to 38 satellites, enhanced operability features, expansion of the TTC network and additional security protection capabilities.

Upgrades of the Galileo Service Facilities are underway as well, notably the evolution of the GNSS Service Center toward the integration of the OS-NMA and HAS capabilities, and the extension of the reference measurement capabilities of the Galileo Reference Centre, by the prime contractor GMV in Spain. The robustness of the SAR service operations, under the prime contractor CNES in France, is also under improvement.

The production of 12 additional Batch 3 Galileo first generation satellites is proceeding, aiming at readiness for launch from mid 2021 onward. Batch 3 satellites are comparable to the 22 FOC satellites launched previously and built by the same prime contractor OHB Systems in Germany. With Batch 3 satellites, Galileo will reach its full constellation capability, including a number of in-orbit spares.

Galileo Batch 3 satellites will be progressively launched with the new Ariane 62 launcher vehicle, the two strap-on solid booster variant of Ariane 6, currently undergoing the final stages of development led by prime contractor ArianeGroup. Meanwhile, France’s space agency CNES is preparing the Ariane 6 launch facilities at Europe’s Spaceport in French Guiana. Ariane 6 is scheduled for its first launch in 2022.

Europe’s new Ariane 6 launch vehicle. (Artist’s concept: ESA)

Toward Galileo Second Generation

The Galileo Programme is fully engaged in the process of developing Galileo 2nd Generation (G2G). Procurement activities for system, satellite and ground segment have been initiated in 2020 with the ambitious goal of starting deployment of the new infrastructure in 2024.

The design of G2G is driven by overarching principles, including backward compatibility, providing an extended portfolio of services and the quality of services, but also the absolute need to meet user demands in a timely and effective manner. The European Commission, in close consultation with EU member states, has converged onto an ambitious set of long term PNT goals for the future European GNSS infrastructures.

G2G Service Portfolio and High-Level Mission Objectives agreed with Programme Stakeholders Service include service evolutions in the areas of signals evolution for increased performance and reduced complexity and power consumption at the user receiver level, time to first-fix, accuracy, authentication and other service attributes, PRS evolutions, advanced timing services, enhanced integration with terrestrial systems (5G/6G), complementarity with external sensors (such as INS, barometer, lidar) and application environments (such as low power devices and internet of things), SAR service evolution, Emergency Warning services, Space Service Volume and Ionosphere Prediction Service.

G2G will build on advanced navigation technology developed over the past 10 years under ESA’s European GNSS Evolution Programme (EGEP) and EU’s Horizon 2020 Programme. This technological leap will allow the early introduction of novel Galileo system features:

• Open service capabilities (reduce power consumption and convergence time)
• High-accuracy evolution (integrity, availability)
• PRS robustness and transmit power
• System and SIS in-orbit flexibility, reconfiguration and time-to-market
• Inter-satellite links (ranging, mission dissemination, command and control)
• SAR second-generation beacons
• Reduce operations and maintenance cost
• Accelerate time-to-market of new services
• Ground technology virtualization and modernization

Acknowledging the changing nature of user requirements, the Galileo second-generation is designed to evolve incrementally and with sufficient flexibility to provide new services or signal features, if and when required, by dynamic reconfiguration of space and ground infrastructure.