Galileo navigation program FOC
Galileo navigation program: FOC (Full Operational Capability)
Galileo is a joint initiative of the European Commission (EC) and the European Space Agency (ESA). Galileo will be Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It will be inter-operable with GPS and GLONASS, the two other GNSS (Global Navigation Satellite Systems). The complete system consists of:
• A space segment of 30 MEO satellites in 3 planes inclined at 56º
• A launch segment to place the satellites into their operational orbits
• A control ground segment for monitoring and control of the satellites
• A mission ground segment managing all mission specific data
• A user ground segment of equipment capable of receiving and using Galileo signals
The Galileo program has been structured into two phases:
1) IOV (In-Orbit Validation) phase: IOV consists of tests and the operation of four satellites and their related ground infrastructure. The first two IOV satellites were launched on Oct. 21, 2011. The second pair of IOV satellites, IOV-3 and IOV-4, were launched on Oct. 12, 2012.
2) FOC (Full Operational Capability) phase: FOC consists of the deployment of the remaining ground and space infrastructure. It includes an initial operational capability phase of 18 operational satellites. The full system will consist of 30 satellites, control centers located in Europe and a network of sensor stations and uplink stations installed around the globe.
Contract kick-off with OHB as the prime of the FOC space segment WP1 (Work Package 1) took place in late January 2010; two years later, again after highly competitive bidding and based on the performance in WP1, OHB was also able win the space segment Work Order 2 contract, thus increasing the total number of satellites to be built to 22. The Galileo FOC project is characterized by an extremely challenging schedule, which foresees a delivery of a finalized satellite every six weeks. 4)
Development of the Galileo Satellites
• July 19, 2021: The first Galileo Second Generation hardware has begun testing, with test versions of the satellites’ navigation payloads undergoing evaluation by Airbus Defence and Space at their Ottobrunn facility in Germany and by Thales Alenia Space at ESA’s ESTEC technical centre in the Netherlands. 5)
- These testbed versions of these new navigation payloads designed by the two companies are undergoing testing of their respective navigation antennas to check whether they meet the ambitious performance levels set for the coming generation of Europe’s satellite navigation system.
- Known as the GPLTBs (Galileo Payload Testbeds), these are development models of the navigation payloads intended for the Galileo Second Generation (G2) satellites.
Figure 2: The GPLTBs are development models of the navigation payloads intended for the Galileo Second Generation (G2) satellites. This is a diagram of the Thales Alenia Space GPLTB, with Airbus Defence and Space producing their own equivalent (image credit: ESA)
- The main difference is that instead of being assembled from space-ready components like an actual satellite payload, the GPLTBs are built up from ‘breadboard’ electronic parts placed in test racks, with a proof-of-concept version of a navigation antenna attached.
- “The goal with these test campaigns are to prove their design concept early, and anticipate any technical issues that might arise as early as possible,” explains Cédric Magueur, ESA’s Payload Manager for the Thales G2 satellites.
- “These campaigns also allow to develop and validate new performance measurements concepts for these new generation of complex navigation payloads,” adds Dirk Hannes, ESA’s Payload Manager for the Airbus G2 satellites. “This will allow us to optimize the production efficiency of the Flight Model series.”
- Cédric adds: “Results from the testing will feed into the up-coming Preliminary Design Review for the new satellites, backing up the analyses by the companies with solid measurements. Such early testing also supports the ambitious timescale for the development and construction of G2 satellites, with the first satellites planned to reach orbit by the middle of this decade.”
- Galileo is Europe’s civil global satellite navigation constellation, currently the world’s most precise satnav system, offering meter-scale accuracy to more than 2 billion users around the globe. There are 26 Galileo satellites in orbit, scheduled to be joined by other 12 satellites starting to be deployed by the end of this year.
- Next will come the first 12 G2 satellites, featuring enhanced navigation signals and fully digital payloads. This new generation will be made up of two independent families of satellites meeting the same performance requirements, produced by Thales Alenia Space in Italy and Airbus Defence and Space in Germany.
- Airbus Defence and Space’s GPLTB is currently undergoing radiated testing at the company’s Ottobrunn facility, inside a Compact Antenna Test Range (CATR). Meanwhile the Thales Alenia Space GPLTB is about to start testing inside ESTEC’s own Hybrid European Radio Frequency and Antenna Test Zone (Hertz) chamber.
- These are metal-walled chambers kept isolated from external radio interference, whose inner walls are studded with foam pyramids to minimize radio frequency signal reflections, mimicking the void of space.
- “Up until now all GPLTB testing has taken place by plugging them into test boards,” adds Cédric. “These test campaigns mark the first time that their performances will be confirmed in terms of radiating signals.”
- Radio-frequency radiation forming of the navigation signals takes place through a combination of digital processing and interaction with the antenna, so practical radio frequency testing is essential to check the true payload performance.
- Cédric explains: “In our first phase we will perform near-field measurements directly around the antenna to measure all the characteristics of the signal shape, to check it matches previous conductance tests. Then via computation we can derive its far-field performance.
- “In the second test phase the actual far-field measurements will be performed, using another feature of the chambers. Thanks to a pair of specially-shaped paraboloid reflectors, the signal from the testbed can be reshaped as if it has travelled the very long distance that actual Galileo signals need to stretch, all the way from an altitude of 23,222 km down to Earth’s surface.”
- Dirk comments:“On the Airbus side the methodology is substantially the same, except the far-field measurement are currently being performed, to be followed by the near-field.
Figure 3: Airbus Galileo Second Generation satellites. Galileo Second Generation will be made up of two independent families of satellites meeting the same performance requirements, produced by Thales Alenia Space in Italy and Airbus Defence and Space in Germany (image credit: Airbus Defence and Space)
Figure 4: Thales Galileo Second Generation satellites (image credit: Thales Alenia Space)
• June 3, 2021: Europe’s Galileo satellite navigation constellation is set to grow. Later this year the first two out of 12 ‘Batch 3’ Galileo satellites will be launched by Soyuz from French Guiana. Their last step on the way to launch is situated beside sand dunes on the Dutch coast: the ESTEC Test Centre, which is Europe’s largest satellite test facility. 6)
- All but two of the 26 Galileo satellites already in orbit underwent pre-flight testing at this 3000 m2 environmentally-controlled complex, hosting test equipment to simulate all aspects of spaceflight. The Test Centre is operated and managed by European Test Services for ESA.
- All 12 Batch 3 satellites – functionally similar to the Full Operational Capability satellites already in orbit – are scheduled to come here from OHB in Germany to assess their readiness for space, before heading on to French Guiana.
- The first pair of these satellites were already at ESTEC when the COVID-19 pandemic began last year. Testing was briefly interrupted as the Test Centre was closed, but resumed once safety measures were put in place.
- Testing of this first pair was completed in April, and they are now in storage on site. Two more Galileo satellites have since arrived with another due to join them this month.
- Newly-arrived satellites begin by undergoing a two-week immersion in vacuum and temperature extremes that mimic the conditions it faces in space. This ‘thermal–vacuum’ test takes place inside a 4.5 m-diameter stainless steel vacuum chamber called Phenix. An inner box called the ‘thermal tent’ has sides that are heated to simulate the Sun’s radiation or cooled down by liquid nitrogen to create the chill of Sunless space.
- Another test involves switching on all satellite systems within the Maxwell Test Chamber, which is fitted with shielded walls blocking out all external electrical signals and spiky, radio-absorbing ‘anechoic’ material that line the chamber to prevent signal reflections. Kept isolated in this way as though floating in infinite space allows ‘electromagnetic compatibility’ testing. Each satellite is switched on to check all its systems can operate together without harmful interference.
- Then, once the satellites’ solar wings are fitted, which come from Airbus Netherlands in nearby Leiden, they can undergo ‘mass properties testing’. This involves measuring to check their centre of gravity and mass are aligned within design specifications. The more precisely these are known, the more efficiently each satellite’s orientation can be controlled with thruster firings in orbit, potentially elongating its working life by conserving propellant.
- Each satellite also undergoes acoustic testing in the LEAF (Large European Acoustic Facility), effectively the largest sound system in Europe.
- A quartet of noise horns are embedded in one wall of this 11 m-wide, 9 m-deep and 16.4 m-high chamber, generating sound by passing nitrogen gas through the horns, surpassing 140 decibels in all. Accelerometers placed within the satellite checked for potentially hazardous internal vibration during this trial by sound.
- Once each satellite’s test campaign is over, they are shipped to Europe’s Spaceport in French Guiana and prepared for launch. The two tested spacecraft will leave to Kourou in October, to be launched at the end of the year.
- Summer 2020 saw the start of construction of a new 350 m2 cleanroom for the ESTEC Test Centre. Most of the time the ESTEC Test Centre has several other test items as well as Galileo satellites within its walls simultaneously.
- Complex planning and traffic management are necessary to ensure every project get access to the facility they need at the time they need it. So sufficient room is required to accommodate the different customers and allow their movement between test facilities.
Figure 5: Galileo Batch 3 satellites at OHB in Bremen (image credit: OHB)
• May 28, 2021: Acting on behalf of the European Commission, ESA has signed two contracts for an overall amount of €1.47 billion, to design and build the first batch of the second generation of Europe’s Galileo navigation satellites. 7)
- Following an intense process of open competition, these contracts have been awarded to Thales Alenia Space (Italy) and Airbus Defence & Space (Germany) to create two independent families of satellites amounting to 12 Galileo Second Generation satellites in total.
- “Galileo is a major success for Europe, and these contracts ensure that it is going to be around for a long time to come,” comments Paul Verhoef, ESA Director of Navigation. “The Galileo Second Generation will represent a further step forward with the use of many innovative technologies to guarantee unprecedented precision, robustness and flexibility of the system for the benefit of users worldwide.”
- Galileo is Europe’s civil global satellite navigation constellation, currently the world’s most precise satnav system, offering meter-scale accuracy to more than 2 billion users around the globe. With improved accuracy, the new generation should be able to offer decimeter-scale precision positioning to all.
- These Galileo Second Generation (G2) satellites will revolutionize the Galileo fleet, joining the 26 first generation Galileo satellites in orbit today plus the 12 ‘Batch 3’ satellites currently in production and testing. The first launch of these Batch 3 satellites will take place later this year.
- The new G2 satellites will be constructed in a short time scale with their first launch expected in less than four years, allowing them to commence operations in space as soon as possible. The G2 satellites will gradually join the existing constellation, but will be much larger than existing satellites. Using electric propulsion for the first time, and hosting an enhanced navigation antenna, their fully digital payloads are being designed to be easily reconfigured in orbit, enabling them to actively respond to the evolving needs of users with novel signals and services.
- New on-board technologies include electric propulsion to propel the satellites from the orbit in which they will be launched to the final operational orbits, allowing two satellites to be launched at once despite their increased mass. Inter-satellite links between the satellites will let them routinely cross-check their performance and reduce their dependency on the availability of ground installations.
- The satellites will also feature a more powerful navigation antenna, more precise onboard atomic clocks, as well as advanced jamming and spoofing protection mechanisms to safeguard Galileo signals.
- Thanks to G2, it will be possible for navigation devices such as smartphones to acquire the signal faster and access services more quickly upon switching on their devices, with lower power consumption. This will open up new perspectives for many new devices to offer positioning capabilities, a true revolution for emerging self-driving cars, autonomous drones and the whole ‘Internet of things’.
- G2 will also offer enhanced services for search and rescue, including two-way communications to the person in trouble. And a new emergency communications capability will enable authorities to warn users in affected regions of imminent dangers such as tsunamis or earthquakes. Such warnings could be sent anywhere on Earth, independently of telecommunication providers, by using Galileo navigation signals as a one-way messaging service.
- Overall, the G2 satellites will incorporate numerous technology upgrades, developed through EU and ESA research and development programs. But the Galileo G2 system will result from a series of seamless upgrades and changes to the G1 system currently in place, without interruption to any of its services.
- The Galileo system will be operated by the EU Agency for the Space Program, EUSPA, based in Prague. ESA and EUSPA are partnering on the development and operations of Galileo.
- ESA is in charge of the design, development, procurement, qualification of Galileo satellites and the associated ground infrastructure on behalf of the European Union, the system owner.
Figure 6: Galileo Second Generation. Galileo is Europe’s civil global satellite navigation constellation, currently the world’s most precise satnav system, offering meter-scale accuracy to more than 2 billion users around the globe. With improved accuracy, the new generation should be able to offer decimeter-scale precision positioning to all (image credit: ESA)
• January 20, 2021: Today the EC (European Commission) awarded two contracts for 12 Satellites (6 satellites each) for a total of EUR €1.47 billion, to Thales Alenia Space (Italy) and Airbus Defence & Space (Germany) following an open competition. 8)
- With this, the Commission is initiating the launch of the 2nd Generation of Galileo, the European satellite positioning system. The aim is to keep Galileo ahead of the technological curve compared to global competition and maintaining it as one of the best performing satellite positioning infrastructures in the world while strengthening it as a key asset for Europe’s strategic autonomy.
- The first satellites of this second generation will be placed in orbit by the end of 2024. With their new capabilities relying on high innovative technologies (digitally configurable antennas, inter- satellites links, new atomic clocks technologies, use of full electric propulsion systems), these satellites will improve the accuracy of Galileo as well as the robustness and resilience of its signal, which will be key for the upcoming digital decade as well as more security & military usage.
- With the Galileo satellite navigation system, Europe operates a state-of-the-art system in positioning, timing and navigation that is recognized worldwide as the most performant of this kind. In operation since 2016, Galileo provides signal services to 2 billion users around the globe. 26 satellites are currently in orbit, with 2 additional satellites due for launch in Q3 2021.
- In May 2018, the Commission launched the tender procedure to procure a first batch of 12 second-generation satellites through a competitive dialog, with the objective of signing two contracts (double source) of 6 satellites each. The tender procedure was run by the European Space Agency (ESA) by delegation. After 2 months of detailed technical and financial evaluation of the industrial offers, ESA recommended to the Commission to proceed with TAS (Thales Alenia Space) and Airbus Defence & Space that represent the best technical and financial offers. The three industrial bidders were notified yesterday.
• 2010: For the Galileo FOC development phase, OHB System of Bremen, Germany teamed with SSTL (Surrey Satellite Technology Ltd.), UK. Within this team, OHB-System is the prime contractor and is responsible for the development of the 22 spacecraft. SSTL is fully responsible for the satellite payloads. The system level activities will be led by OHB-System, making use of the experience gained by SSTL through its GIOVE-A activities. 9)
ESA is already procuring 4 satellites from Astrium through its IOV (In-Orbit Validation) program which brings the number of operational Galileo satellites now under contract to 18.
Spacecraft of the FOC series:
The production of the spacecraft series, with a delivery schedule of each pair of satellites in periods of 3 months, requires an assembly line production technique to meet the time table. This can only be achieved by implementing a modular satellite design.
The FOC satellites, 22 in total, provide the same operational services as their predecessors, but they are built by a new industrial team: OHB in Bremen, Germany build the satellites with Surrey Satellite Technology Ltd in Guildford, UK contributing the navigation payloads.
Legend to Figure 8: The navigation satellite’s pair of 1 m x 5 m solar wings, carrying more than 2500 state-of-the-art gallium arsenide solar cells, will power the satellite during its 12 year working life. 10)
The design of the 22 Galileo FOC satellites is quite different with respect to that of their four Galileo IOV (In-orbit Verification) counterparts. For technical and cost reasons, only half of the units aboard were re-used from IOV. Part of the rationale are also more demanding requirements for FOC compared with IOV, e.g. an increased RF signal output power level, tougher radiation requirements, and harsher launch load requirements to name a few. Hence, qualification on subsystem and system level had to be done from scratch (Ref. 4).
Fulfilment of ESA's FOC satellite requirements was achieved through a simple and robust design, leading to a satellite of ~720 kg with a provided power production of 1.9 kW (end of life), which provides navigation signals in L1, E5, and E6 bands, as well as Search-and-Rescue services. The FOC satellite design is depicted in Figure 9.
A lot of OHB's development work went into optimizing the design for series production. It was identified that in order to meet the production cadence requirement of six weeks, parallelization of work on each satellite would have to be achieved. As this is very hard to achieve at late stages of integration and testing of a satellite, the focus was put in particular on the early stages of MAIT (Manufacturing, Assembly, Integration, and Testing).
The satellites are integrated in seven modules, depicted also in Figure 10:
• the propulsion module (integrated at the propulsion supplier, Moog Inc.)
• the solar generator module (integrated at the solar generator supplier)
• clock, antenna, and payload core module (integrated at SSTL, OHB's co-prime, responsible for the payload, located in Guildford, UK)
• the center and the platform core modules (integrated at OHB's premises in Bremen, Germany).
Work on these seven modules can be executed independently from each other and in parallel to each other. A good example for that is the propulsion module. While in most satellites, the propulsion system is distributed over the entire spacecraft, the modularity intended for Galileo FOC let OHB designers to mount all the propulsion-related systems on one panel, which can be integrated and replaced also late in the MAIT process (as depicted in Figure 9). The big access panel in the launch dispenser-facing side of the satellite increases the ease of access into the satellite, also at late stages of the assembly.
In the next step of integration after module integration, the seven modules form the platform and the payload (see Figure 2), which also can be treated independently from each other and in parallel to each other (payload at SSTL, platform at OHB). Final integration of payload and platform and system level tests are then also carried out at OHB. Subsequently, the integrated and tested satellites are shipped to ETS (European Test Services) in Noordwijk, The Netherlands, for the environmental test campaigns.
Development work was based on early availability of functional models of the board computers. These were used in subsystem breadboards to facilitate software development with hardware in the loop as early on as possible. Further development work was carried out in two thermal development models that focussed on the two thermally critical areas: firstly, the clock panel, where clock temperature stability was demonstrated, and secondly the area of the travelling wave tubes, where sufficient high dissipation on limited radiator area was validated.
On system level, a flat-sat engineering model was employed to check out inter-subsystem compatibility and interaction. A further payload-only engineering model was employed by SSTL at their premises for payload-level development work.
MAIT (Manufacturing, Assembly, Integration, and Testing): The MAIT approach picks up on the design of the satellite and focuses on the series production and the production cadence as well. The production is based on an island mode, while the check-out equipment and ground support equipment stays in place, it is the satellites that move from station to station. The activities that are executed at a given station are trimmed to give all stations more or less the same stay duration. After that duration, all satellites move forward one station. Primary goal is to keep the flow of satellites going, meaning to avoid “clogging” the production pipeline, as this would have impact on all previous islands, which cannot turn to the next satellite in line, whereas all succeeding islands or stations would “run dry”. Hence margin for trouble shouting must be taken into account. For larger issues in the production pipeline, there is a so-called “recovery island” foreseen, which is equipped with all types of ground support equipment which can handle problems that take several days or even weeks to resolve while the rest of the pipeline continues normally.
Table 2: Key parameters of the Galileo spacecraft 11)
Figure 11: The main antenna of the FM2 satellite is being inspected at ESTEC prior to mass property testing in August 2013 (image credit: ESA, Anneke Le Floc'h) 12)
Nominal orbit of the Galileo constellation: The Galileo constellation is composed of a total of 30 MEO (Medium Earth Orbit) satellites, of which 6 are spares (Figure 1). Each satellite will broadcast precise time signals, ephemeris and other data. The Galileo satellite constellation has been optimized to the following nominal constellation specifications:
- Circular orbits (satellite altitude of 23,222 km), orbital inclination of 56°, three equally spaced orbital planes.
- Eight operational satellites, equally spaced in each plane, two spare satellite (also transmitting) in each plane.
Launch: On August 22, 2014, the first two Galileo FOC satellites,FOC-1 (FM1) and FOC-2 (FM2), were launched from Kourou on the Soyuz ST-B vehicle (flight VS09), operated by Arianespace. 13)
Unfortunately, the orbit injection of the FOC spacecraft didn't occur as planned and the satellites did not reach their intended orbital position.
The liftoff and first part of the mission proceeded nominally, leading to the release of the satellites according to the planned timetable, and reception of signals from the satellites. It was only a certain time after the separation of the satellites that the ongoing analysis of the data provided by the telemetry stations, operated by ESA and the French space agency, CNES, showed that the satellites were not in the expected orbit.
The targeted orbit was circular, inclined at 56º with a semi major axis of 29,900 km. The satellites are now in an elliptical orbit, with an eccentricity of 0.23, a semi major axis of 26,200 km and inclined at 49.8º.
According to the initial analyses, an anomaly is thought to have occurred during the flight phase involving the Fregat upper stage, causing the satellites to be injected into a noncompliant orbit.
Figure 12: Photo of the Galileo FOC-3 and FOC-4 satellites fitted onto dispenser (image credit: ESA/CNES/ARIANESPACE-Service Optique CSG) 14)
Figure 13: Illustration of satellite configurations in various mission phases (image credit: OHB System)
Launch: The seventh and eighth Galileo satellites (FOC-3 and FOC-4) were successfully launched together on March 27, 2015 (21:46:18 UTC) atop a Soyuz-STB/Fregat vehicle (VS11) from Europe's Spaceport (Kourou, ELS) in French Guiana. 15) 16)
All the Soyuz stages performed as planned, with the Fregat upper stage releasing the satellites into their target orbit close to 23, 500 km altitude, around 3 hours 48 minutes after liftoff. Shortly thereafter, the two satellites sent their first signals from orbit, which were received by the CNES control center in Toulouse. 17)
Following initial checks, run jointly by ESA and France’s CNES space agency from the CNES Toulouse center, the two satellites will be handed over to the Galileo Control Center in Oberpfaffenhofen, Germany and the Galileo in-orbit testing facility in Redu, Belgium for testing before they are commissioned for operational service. This is expected in mid-year.
Figure 14: Artist's view of the protective launcher fairing which jettisoned at 3 min 29 sec after launch, revealing the two Galileo satellites attached to their dispenser atop the Fregat upper stage (image credit: Arianespace, ESA)
All the Soyuz stages performed as planned, with the Fregat upper stage releasing the satellites into their target orbit close to 23,500 km altitude, around 3 hours and 48 minutes after liftoff. Shortly thereafter, they sent their first “sign of life” to ESOC (European Space Operation Center) in Darmstadt, Germany. Over the next few days, the two satellites will also be undergoing preliminary function testing.
Two further Galileo satellites are still scheduled for launch by end of 2015. These satellites have completed testing at ESA/ESTEC in Noordwijk, the Netherlands, with the next two satellites also undergoing their own test campaigns.
Next year the deployment of the Galileo system will be boosted by the entry into operation of a specially customized Ariane 5 launcher that can double, from two to four, the number of satellites that can be inserted into orbit with a single launch.
Launch: The Galileo-11 and -12 satellites (FOC-7 and FOC-8) were launched atop a Soyuz STB/Fregat rocket at 11:51:56 GMT on December 17, 2015 from Kourou, Europe’s Spaceport in French Guiana. 21)
Launch: The Galileo-13 and -14 satellites (FOC-9 and FOC-10) lifted off together at 08:48 GMT on May 24, 2016 atop a Soyuz rocket from French Guiana. The twin Galileo spacecraft were deployed into orbit close to 23,522 km altitude, at 3 hours and 48 minutes after liftoff. The coming days will see a careful sequence of orbital fine-tuning to bring them to their final working orbit, followed by a testing phase so that they can join the working constellation later this year. 22)
- “Today’s launch brings Europe’s Galileo constellation halfway to completion, in terms of numbers,” remarked Paul Verhoef, ESA’s Director of the Galileo Program and Navigation-related Activities. “It is also significant as Galileo’s last flight by Soyuz this year before the first launch using a customized Ariane 5 to carry four rather than two satellites each time – which is set to occur this autumn.”
- Known by their nicknames Danielè and Alizée, another two Galileo FOC satellites developed and built by OHB System AG, have been successfully launched on board a Soyuz launcher, which lifted off from the Kourou Space Center in French Guiana. 23)
Launch: On November 17, 2016 (13:06 :48 UTC), a quartet of Galileo satellites (Galileo 15-18), each with a mass between 715 kg and 717 kg, and a combined liftoff mass of 2,865 kg, was launched and deployed by Ariane 5 into a circular orbit during a mission lasting just under four hours. The Ariane 5 launch, designated Flight VA233 in Arianespace’s numbering system, was from the Kourou Spaceport in French Guiana. 24) 25)
Flight VA233 marked Arianespace’s first use of its heavy-lift Ariane 5 to loft Galileo satellites, following seven previous missions with the company’s medium-lift Soyuz. The Soyuz vehicles carried a pair of Galileo spacecraft on each flight, delivering a total of 14 navigation satellites into orbit since 2011.
The Galileo satellites are at their target altitude, after a flawless release from the new dispenser designed to handle four satellites. Over the next few days, engineers will nudge the satellites into their final working orbits and begin tests to ensure they are ready to join the constellation. This is expected to take six months or so. This mission brings the Galileo system to 18 satellites.
Figure 15: Above Earth's atmosphere, Ariane’s aerodynamic fairing is jettisoned and the four Galileo satellites ‘see’ space for the first time (image credit: ESA, P. Caril) 26)
Launch: On December 12, 2017, a quartet of Galileo satellites (Galileo 19-22), each with a mass between 715 kg and 717 kg, were launched on Ariane-5 ES in Kourou at 18:36 GMT (flight VA240). The first pair of satellites was released almost 3 hours 36 minutes after liftoff, while the second pair separated 20 minutes later. 27) 28)
- The satellites were released into their target 22,922 km altitude orbit by the dispenser atop the Ariane-5 upper stage. In the coming days, this quartet will be steered into their final working orbits. There, they will begin around six months of tests – performed by the European Global Navigation Satellite System Agency (GSA) – to check they are ready to join the working Galileo constellation.
- This mission brings the Galileo system to 22 satellites. Initial Services of the constellation began almost a year ago, on 15 December 2016.
- “Today’s launch is another great achievement, taking us within one step of completing the constellation,” remarked Jan Wörner, ESA’s Director General. “It is a great achievement of our industrial partners OHB (DE) and SSTL (GB) for the satellites, as well as Thales Alenia Space (FR, IT) and Airbus Defense and Space (GB, FR) for the ground segment and all their subcontractors throughout Europe, that Europe now has a formidable global satellite navigation system with remarkable performance.”
- Paul Verhoef, ESA’s Director of Navigation, said: “ESA is the design agent, system engineer and procurement agent of Galileo on behalf of the European Commission. Galileo is now an operating reality, so, in July 2017, operational oversight of the system was passed to the GSA. Accordingly, GSA took control of these satellites as soon as they separated from their launcher, with ESA maintaining an advisory role. This productive partnership will continue with the next Galileo launch, by Ariane-5 in mid-2018.”
- “Meanwhile, ESA is also working with the European Commission and GSA on dedicated research and development efforts and system design to begin the procurement of the Galileo Second Generation, along with other future navigation technologies.”
- Next year’s launch of another quartet will bring the 24-satellite Galileo constellation to the point of completion, plus two orbital spares.
Launch: On 25 July 2018 (11:25:01 UTC), a quartet of Galileo satellites (23-26, Galileo FOC 19-22) was launched on an Ariane-5 ES vehicle (Flight VA244) of Arianespace from Kourou. The first pair of 715 kg satellites was released almost 3 hours 36 minutes after liftoff, while the second pair separated 20 minutes later. 29) 30)
They were released into their target 22 922 km-altitude orbit ( MEO, 56º inclination) by the dispenser atop the Ariane-5 upper stage. In the coming days, this quartet will be steered into their final working orbits by the French space agency CNES, under contract to the Galileo operator SpaceOpal for the European Global Navigation Satellite System Agency (GSA). There, they will begin around six months of tests by SpaceOpal to verify their operational readiness so they can join the working Galileo constellation.
In July 2017, ESA officially transferred the supervision of Galileo in-orbit operations to the European Global Navigation Satellite Systems Agency (GSA), on behalf of the European Union. After the VA244 launch, the GSA will be responsible for operating the satellites as soon as they are separated from the launcher. These operations of setting up and operating the system will be done in collaboration with ESA.
The constellation will count 24 operational satellites plus in-orbit spares, of which 22 already have been put into orbit by Arianespace.
Figure 16: Completing the constellation. On 25 July 4 Europe’s next four Galileo satellites will be launched into orbit by Ariane 5 from Europe’s Spaceport in French Guiana. With this launch the Galileo constellation will reach 26 satellites in space, completing the constellation in overall numbers although further launches are needed to place back-up satellites in orbit. The launch comes at a time when Galileo is into its second year of Initial Operations, with a signal that is better than expected and that is now usable in all new mobile phones. This video looks at Galileo’s story so far and the way forward, interviewing Paul Verhoef, ESA Director of Navigation, and Valter Alpe, Galileo’s Satellite Production and Launch Campaign Manager (video credit: ESA, Published on 24 July 2018)
• September 8, 2021: An experimental satellite navigation receiver station high atop Spain’s Mallorca island has opened up a novel view of the ever-changing face of the sea. By picking up satnav signals from the far horizon as they bounce off ocean waves, the receivers are able to measure sea surface height down to a scale of centimeters. 31)
Figure 17: Test campaign setup. A pair of satnav receivers atop Mallorca picked up slant angle signals from GNSS satellites to perform reflectometry. Because of the shallow angle, the signals were more likely to maintain coherence than standard near-vertical-angle reflectometry, allowing carrier phase processing to reach an accuracy down to a scale of centimeters. The results were compared to Sentinel-3 altimetry data and an in-situ oceanography buoy (image credit: Institute for Space Studies of Catalonia)
- “We set up a pair of satnav receivers in a near-horizontal orientation, 1400 m above sea level atop Mallorca’s highest peak, 4 km from the coast,” comments Estel Cardellach of the Institute for Space Studies of Catalonia.
- “Our aim was to receive signals from Galileo, GPS and other Global Navigation Satellite Systems (GNSS) in a way that isn’t possible using standard commercial receivers. We pick up satnav signals that have reflected off the sea surface at very slanted, nearly horizontal geometries, then use these results to derive sea surface height and shape.”
- “The basic idea behind GNSS ‘reflectometry’ is not new,” explains ESA microwave engineer Manuel Martín-Neira, who first devised the technique in the early 1990s.
- The concept grew out of the well-established practice of radar altimetry, where radar pulses get bounced down from satellites in orbit to measure the precise contours of Earth’s surface. The Copernicus Sentinel-3 pair are the latest contributors to a global altimetry dataset that extends back three decades.
Figure 18: This localization buoy was placed in the sea off Mallorca to help validate results from the GNSS reflectometry test campaign. The satnav receivers can be seen atop the Mallorca skyline (image credit: Institute for Space Studies of Catalonia)
- Manuel had the idea that the satnav signals continuously raining down on Earth from multiple GNSS satellite constellations could be made use of in a comparable manner: comparing original and reflected satnav signals could yield altitude along with additional environmental information. Since then multiple space missions have proven the method.
- He notes: “Standard GNSS reflectometry works like radar altimetry, with orbital satellites receiving reflected signals from straight down, on a nearly vertical orientation. Instead this test campaign has employed a slant geometry, making use of shallow-angle reflected signals from GNSS satellites low on the far horizon.
Figure 19: An experimental satellite navigation receiver station high atop Spain’s Mallorca island has opened up a novel view of the ever-changing face of the sea. By picking up satnav signals from the far horizon as they bounce off ocean waves, the receivers are able to measure sea surface height down to a scale of centimeters. A pair of satnav receivers was positioned in a near-horizontal orientation, 1400 m above sea level atop Mallorca’s highest peak, 4 km from the coast, seen here with grazing sheep (image credit: Institute for Space Studies of Catalonia)
- “Why do this? Because while a vertical geometry gives a very rough sea surface, at shallow geometries the sea appears more like a mirror – think of the way Venetian blinds can seem variously open or closed depending on how you look at them. This surface smoothness means the reflected signals remain more coherent in turn, potentially allowing us to obtain much higher precision distance measurements.”
- This approach is borrowed from a traditional satnav method to boost precision: instead of processing the pseudo-random codes embedded in satnav signals, so-called ‘carrier phase’ processing utilizes the much higher-frequency satnav signals themselves, potentially increasing the resulting accuracy from a scale of several meters down to centimeters – although in practice atmospheric effects still need accounting for.
- Estel says: “Our test campaign was supported through ESA’s Open Space Innovation Platform to help prepare for a new small reflectometry mission called PRETTY (Passive REflecTomeTry and dosimetry), which will use the same slant geometry in orbit. This miniature ESA CubeSat is being developed by RUAG in Austria and the University of Graz.”
Figure 20: The PRETTY CubeSat will perform slant geometry GNSS reflectometry from in orbit. This miniature ESA CubeSat is being developed by RUAG-Austria and the University of Graz. PRETTY is scheduled to launch in the second half of 2022 (image credit: ESA)
- Results from the reflectometry testing will be checked against Sentinel-3 altimetry data of the offshore test areas, along with an oceanographic buoy deployed specially to provide ‘ground-truth’ results.
- The Institute for Space Studies of Catalonia’s Institute of Space Science unit (IEEC/ICE-CSIC) led the campaign, with the Mediterranean Institute of Advanced Studies (IMEDEA-CSIC/UIB) and Balearic Islands Coastal Observing and Forecasting System (SOCIB) working on the buoy deployment, data recovery, archiving, dissemination and analysis. The German Aerospace Center’s Institute for Solar-Terrestrial Physics (DLR-SO) is overseeing analysis of tropospheric and ionospheric interference.
- The receiver station was set up within the military zone of the 7th Aerial Surveillance Squadron of the Spanish Air Force, who also provided electrical power and logistical support.
- “Our test campaign is now over, having run from April to July,” adds Estel. “The main reason we aren’t observing for longer still is simply the sheer amount of raw data gathered by our receivers: 320 MB per second, adding up to more than a terabyte per hour. While our preliminary indications look promising, it is still going to take several months for us to properly process this gargantuan dataset.”
- The testing has already had one significant outcome, explains Manuel: “The main goal of this campaign was to test out how to process data from the PRETTY mission. As we did so, using dual satnav frequencies, we realized the longer-wavelength L5 gives increased coherence compared to L1. So we have proposed switching the working frequency of the single-frequency PRETTY from L1 to L5. Such a change, subject to final technical approval, should greatly enhance the mission’s performance.”
Figure 21: An experimental satellite navigation receiver station high atop Spain’s Mallorca island has opened up a novel view of the ever-changing face of the sea. By picking up satnav signals from the far horizon as they bounce off ocean waves, the receivers are able to measure sea surface height down to a scale of centimeters. A pair of satnav receivers was positioned in a near-horizontal orientation, 1400 m above sea level atop Mallorca’s highest peak, 4 km from the coast. The aim was to receive signals from Galileo, GPS and other Global Navigation Satellite Systems (GNSS) in a way that isn’t possible using standard commercial receivers. By picking up coherent satnav signals that have reflected off the sea surface at very slanted, nearly horizontal geometries, the campaign can use these results to derive sea surface height and shape to high accuracy (image credit: Institute for Space Studies of Catalonia)
• June 24, 2021: Under the Advanced Shipborne Galileo Receiver Double Frequency (ASGARD) project the technology multinational GMV is collaborating with the defence and security company Saab, to develop a new civil, legislation-compliant, Galileo-signal-using maritime receiver. 32)
- Co-funded by EUSPA (former GSA), ASGARD aims to boost Galileo take up in maritime transport by developing shipborne e-GNSS (European GNSS) data-processing receivers. Ships operating under the International Convention for the Safety of Life at Sea (SOLAS) have to be fitted with a maritime GNSS receiver compliant to the international standards of the International Maritime Organization (IMO).
- GNSS technology is widely used both for ship navigation and positioning applications (traffic surveillance and management, search and rescue, control of fishery vessels, port operations or marine engineering). GNSS's higher capabilities in comparison with traditional maritime navigation methods have made it the preferred navigation resource in many maritime applications.
- In the transport sector as a whole a growing number of regulations enforce GNSS use. Maritime transport is no exception; it is now bound to fit a Positioning, Navigation and Timing (PNT) system that is interoperable in any part of the world. PNT systems are now an obligation in many maritime activities; countries are therefore bound to provide this service for the community and maritime traffic, as a navigation aid in keeping with international recommendations and regulations.
- Satellite navigation can therefore boost the efficiency, safety, and optimization of maritime transport. Galileo and EGNOS, the European Union satellite systems, are making priceless inputs here, with applications taking in all the following: port operations and navigation, localization of spills, improved control of maritime traffic, localization of catastrophes, maritime rescue, ship tracking, improved logistics, ship port approaches, automation, and more efficient port dredging.
- The development of shipborne multi-system radio-navigation receivers (MSR) is now taking a new approach, aiming to provide resilient PNT to improve safety and navigation efficiency. The MSR covers all the shipborne navigation systems and equipment that apply or provide PNT and associated integrity and state information. It calls for support of at least two independent radio-navigation systems; this offers a chance to encourage the use and take-up of e-GNSS (both Galileo and EGNOS) in maritime equipment.
- In this context GMV and Saab will be developing a double frequency multi-constellation maritime receiver navigation system (capable of receiving signals simultaneously from Galileo and other satellite positioning systems) complying with European and international legislation, with the unique ability to provide an additional layer of system safety using Galileo's Open Service-Network Message Authentication (OS-NMA).
- Galileo OS-NMA provides digital signatures of the Galileo Open Service Navigation Messages. It gives the mean for Galileo OS-MNA capable receivers to verify Galileo navigation data received is coming from a Galileo satellite and has not been falsified/spoofed. This verification method provides the Galileo constellation with strong protection, turning it into a more secure and solid GNSS.
- The new maritime receiver represents a new generation of GMV's Galileo receivers and will be integrated into a Saab navigation system in a format that is already well known by the maritime industry. The receiver will be tested according to the requirements of the European Maritime Equipment Directive for GNSS receivers.
- It will additionally be exposed to sophisticated spoofing tests, before being put through a shipborne field test campaign. In addition to coordinating the project GMV will also be responsible for the analysis and consolidation of ASGARD equipment requirements for maritime navigation and its design, implementation, and validation.
- “As with all ESA’s main GNSS scientific test campaigns, ESA will archive this precious data at the GNSS Science Support Centre based at ESAC in Spain, a facility of ESA’s Navigation Science Office,” comments Javier Ventura-Traveset, Head of the Office. This will enable long-term dataset preservation in support of future GNSS reflectometry missions.”
Open Space Innovation Platform: opening ESA to new ideas
- Leopold Summerer, heading ESA’s Advanced Concepts and Studies Office adds: “This project is a good example of OSIP’s core concept: that we receive good ideas from smart people outside ESA, then take rapid action. In this case the idea for the experiment was submitted last year, was quickly matured and judged excellent, then implemented in record time – in the service of one of our future missions.”
• June 10, 2021: GMV has been awarded by the European Union Agency for the Space Program (EUSPA) with the contract for the implementation of the Galileo High Accuracy Data Generator (HADG), which will be the facility in charge of generating the high-accuracy corrections data to enable the provision of the Galileo High Accuracy Initial Service (HAS). 33)
- The objective of the HADG is to ensure the continuous provision of HAS data with a proper rate, accuracy, availability, continuity and latency. The data will encompass orbit and clock corrections, biases, quality indicators and service parameters.
- The HADG contract addresses a key infrastructure development under the Galileo program. The Galileo HAS, after all, together with the Open Service Authentication (OSNMA) and the Commercial Authentication Service (CAS), is one of Galileo’s standout services, setting it apart from other GNSSs like GPS or GLONASS.
- As defined by the Galileo HAS Implementation Decision published by the European Commission, and further detailed in the HAS Information Note recently published by EUSPA, the HAS will be an open access service based on the provision of high accuracy corrections transmitted in the Galileo E6-B signal (E6, data component), at a rate of 448 bit/s per Galileo satellite connected to an uplink station. The data retrieved by the user from the different satellites offering the HAS will be reconstructed allowing the user to achieve an improved positioning performance.
- GMV, as leader of the project will be responsible for core project activities such as the provision of the algorithms for the computation of the high-accuracy corrections, which rely on GMV’s MagicPPP SW suite for Precise Point Positioning. GMV is supported by SIDERTIA in the area of cybersecurity.
- The specification-, design- and development-phases have already been completed and the project is progressing towards the qualification of the system that will enable the execution of the necessary validation activities prior to the HAS initial service declaration (expected in 2022 according to the HAS information note published by EUSPA). This will be a significant accomplishment for Galileo and a new era for the provision of advanced GNSS services in Europe.
- GMV’s leading role of in the Galileo High-Accuracy Service is the culmination of a long race and the result of R&D investment made by GMV in pursuit of cutting-edge GNSS high-accuracy solutions. GMV presented the first version of MagicGNSS in 2008, and it is now the core element selected to leverage Galileo HAS to the most advanced position within the public GNSS systems.
• May 12, 2021: Space is essential to the way we live, work and play. The core mission of EUSPA (European Union Agency for the Space Program) is to implement the EU Space Program and to provide reliable, safe and secure space-related services, maximizing their socio-economic benefits for European society and business. By fostering the development of innovative and competitive upstream and downstream sectors and engaging with the entire EU Space community, EUSPA is driving innovation-based growth in the European economy and contributing to the safety of EU citizens and the security of the Union and its Member States, while at the same time reinforcing the EU’s strategic autonomy. 34)
EUSPA Mission Statement
The mission of EUSPA is defined by the EU Space Program Regulation. EUSPA’s mission is to be the user-oriented operational Agency of the EU Space Program, contributing to sustainable growth, security and safety of the European Union.
Its goal is to:
- Provide long-term, state-of-the-art safe and secure Galileo and EGNOS positioning, navigation and timing services and cost-effective satellite communications services for GOVSATCOM, while ensuring service continuity and robustness;
- Communicate, promote, and develop the market for data, information and services offered by Galileo, EGNOS, Copernicus and GOVSATCOM;
- Provide space-based tools and services to enhance the safety of the Union and its Member States. In particular, to support PRS (Public Regulated Service) usage across the EU;
- Implement and monitor the security of the EU Space Program and to assist in and be the reference for the use of the secured services, enhancing the security of the Union and its Member States;
- Contribute to fostering a competitive European industry for Galileo, EGNOS, and GOVSATCOM, reinforcing the autonomy, including technological autonomy, of the Union and its Member States;
- Contribute to maximizing the socio-economic benefits of the EU Space Programme by fostering the development of a competitive and innovative downstream industry for Galileo, EGNOS, and Copernicus, leveraging also Horizon Europe, other EU funding mechanisms and innovative procurement mechanisms;
- Contribute to fostering the development of a wider European space ecosystem, with a particular focus on innovation, entrepreneurship and start-ups, and reinforcing know-how in Member States and Union regions.
- EUSPA is the operational European Union Agency for the Space Program. It adopts a user-oriented approach to promote sustainable growth and to improve the security and safety of the European Union.
- Over the past twenty years, the European Union has been committed to creating an EU Space Program and infrastructure that is competitive, innovative, and that delivers real benefits to citizens and business alike. Building on these foundations, the European Space Programme has made great leaps forward in recent years, delivering unique services in satellite navigation, Earth observation, and telecommunications, and strengthening both the upstream and downstream sectors.
- As a result, space technology, data and services are indispensable to the daily lives of Europeans. They also play an essential role in supporting the strategic interests of the Union. Space-based services are ubiquitous - we all use them when we use our mobile phones. In addition, a growing number of industries and entrepreneurs look to space to develop solutions to the challenges we face in society. Nevertheless, at EUSPA we believe that we have just scratched the surface of the benefits that space can deliver. We see a future that is very close, where business and society will increasingly look to space as the resource of the future.
- As the link between space and users, EUSPA’s ambition is to become the reference point for all space-related needs in the EU. EUSPA brings all space stakeholders together, allowing them to leverage the synergies of the Space Program’s individual components to deliver the greatest possible benefits to European citizens and business. EUSPA plays a leading role in the EU Space Programme implementation. It promotes space-based scientific and technical progress and supports the competitiveness and innovative capacity of space sector industries within the Union, with a particular focus on small and medium-sized enterprises (SMEs) and start-ups.
- The EU Space Program and the services and applications that it supports, help to advance the European Union’s objectives and to achieve its key policy goals and priorities.
Our values serve as a compass for all our actions and guide how we interact with the world.
- We care about each other and the people we work with; we believe in European values and take our corporate social responsibility seriously.
- We are respectful and diverse. We value and respect people, the environment, the EU institutions and their roles; we encourage diversity and provide equal opportunities for all.
- We are professional. We continuously develop and improve our knowledge, processes, skills and competencies to deliver high quality, cost effective services with integrity and high ethical standards.
- We are innovative. We continuously search for ways to stimulate innovation in our work and the work of our partners to improve our performance and excel in our mission.
- We are reliable. Together, as one team, we are trusted partners to our colleagues across the Agency and to our stakeholders.
- We are accountable. We take responsibility for our work and reach decisions based on due diligence.
- In 2021, in line with the new EU Space Regulation and the growing role of space in supporting EU priorities in terms of growth, competitiveness, sustainability, and security, the EU decided to expand the scope of the former European GNSS Agency (GSA) to include new responsibilities. This resulted in the creation of the EUSPA, which was officially launched on 12 May 2021.
- EUSPA builds on the proven track record of the GSA. In taking on responsibility for various new Space Programme components, EUSPA leverages the GSA’s technical expertise, market intelligence, security know-how, and the extensive EU space-based community that it has built, to create synergies that will take EU space services and applications to a new level both in Europe and around the world.
- The EUSPA story begins with the Galileo Joint Undertaking (GJU) set up in May 2002 by the European Community and the European Space Agency to manage the development phase of the Galileo Program.
- Two years later, the European GNSS Supervisory Authority (GSA) - the GSA's predecessor - was initially established as a Community Agency on 12 July 2004, by Council Regulation (EC) 1321/2004, status amended in 2006 by Council Regulation (EC) No 1942/2006. The European Council took this important step because it recognized the strategic value of Europe having its own independent satellite positioning and navigation program, namely EGNOS and Galileo, and the need to ensure that essential public interests in this field are adequately defended and represented.
- The GSA officially took over all tasks previously assigned to the GJU on 1 January 2007.
- With Regulation (EU) No. 912/2010, which entered into force on 9 November 2010, and subsequently amended by Regulation (EU) No. 512/2014 of 16 April 2014, the GSA was restructured into an agency of the European Union named the European GNSS Agency (GSA).
The Regulatory Framework of the GSA
- The main legal framework currently applicable to the Agency is available in the Register of documents, which you can find here.
• May 01, 2021: Satellites provide crucial data on climate and environmental changes every day. The European Global Navigation Satellite System Agency GSA has now commissioned RUAG Space to conduct a study to increase the accuracy of real-time satellite navigation. 35)
- Satellites provide crucial data on climate and environmental changes every day. The European Global Navigation Satellite System Agency GSA has now commissioned RUAG Space to conduct a study to increase the accuracy of real-time satellite navigation.
- For climate and environmental research, satellites provide extremely important data every day, such as how high sea levels are rising or what effects global warming is having on glacier ice shrinkage in the Alps.
- A new study aims to further increase the accuracy of this space data from climate and environmental satellites. To make this possible, the Prague-based European Global Navigation Satellite System Agency (GSA) awarded a one-million-euro research contract to RUAG Space earlier this year. Headquartered in Zürich, the leading aerospace supplier in Europe is also one of Austria's largest space technology companies, with its headquarters in Vienna.
- To provide precise Earth observation data from space, the satellite's position in space must be known as accurately as possible. To determine the exact position of satellites, RUAG Space's navigation receivers today use the signals from the 22 European Galileo navigation satellites.
- "Currently, there is still untapped potential in the Galileo satellites. They transmit several signals. On one of these signals, a new service, the High Accuracy Service (HAS), will support significantly improved positioning from 2022," explains Martin Auer, who is leading the study at RUAG Space.
- "When this new service goes into operational use, it will need equipment that can do something with it. That's what we're working on." By the end of 2022, RUAG Space will develop a new product in Vienna that will be able to use the new Galileo HAS service.
- Quantum leap: five times more accurate positioning thanks to software update However, navigation receivers from RUAG Space that process Galileo signals already ensure precise positioning. These include the Sentinel-6 environmental satellite, which has been in space since November 2020. It measures the amount of sea level change and provides crucial data on coastal areas at risk from sea level rise.
- "The more accurate the satellite's position can be determined, the more precise the environmental data it collects and provides. With the more accurate data, for example, the danger to coastal cities such as Venice can be predicted more effectively" declared Fiammetta Diani, Head of Market Development at GSA.
- RUAG Space is developing a software update for navigation receivers of the current PODRIX receiver generation already in space, such as those used for Sentinel-6. This will enable these receivers to increase the accuracy of satellite positioning from the current level of about one meter to 20 centimeters. "This is a dramatic improvement - a quantum leap - in accurate satellite positioning that will contribute to much better climate and environmental data," says Heinz Reichinger, the product manager responsible at RUAG Space.
• April 28, 2021: The Agency welcomes the European Parliament's position expressed today, confirming the political agreement on the Space Regulation reached in December 2020 and the creation of the European Union Agency for the Space Program (EUSPA). The EU Space Program, with the largest budget ever for Space - €14.88 billion, encompasses all EU space activities under one roof and will allow for an effective and efficient contribution to the priorities of the European agenda. 36)
- The EU Space Program will ensure the continuity and evolution of the existing flagships Galileo/EGNOS and Copernicus. It will also support new initiatives, in particular the European Union Governmental Satellite Communications (GOVSATCOM), SSA (Space Situational Awareness), and potentially others follow.
- The regulation gives the means to the European Union to maintain its position as a global space power and lay the foundation for EU’s new Space ambition. With the new setup, the European Union will scale up its promotion of innovative downstream applications/technologies, the user and market uptake and the unleash the huge potential of space data and services to develop value-adding applications and services. Moreover, the space data and services provided under the EU Space Programme will support the green and digital transformation, which is the cornerstone for the European recovery initiative.
- Rodrigo da Costa, GSA/EUSPA’s Executive Director, stated: “EUSPA is ready to implement the EU Space Program and join hands with our partners to make the EU space ambitions a reality. We will boost our support to reinforce the dynamic and innovative downstream sector because we want society to benefit even more from space-based services. We will continue delivering and enhancing safe and secure navigation services for the EU citizens and the Member States. We are committed to getting the best out of the EU Space Program components, in particular Galileo, EGNOS, Copernicus and the upcoming GOVSATCOM, and are ready to contribute to new initiatives such as space-based secure connectivity.”
- The EU Agency for the Space Program (EUSPA) replaces and expands on the European Agency for Global Navigation Satellite Systems (GSA) and evolve its mandate.
- In addition to the exploitation management and operational security of EGNOS and Galileo, EUSPA will be in charge of the security accreditation of all the components of the EU Space Program, and of the coordination of user-related aspects of GOVSATCOM, in close collaboration with Member States and other involved entities such as EU Agencies. The Agency will be responsible for promoting the commercial market uptake of Galileo, EGNOS, and now also Copernicus together with the Entrusted Entities of the European Earth Observation program, with a special focus on the synergies of all components of EU Space.
- The EU Space Program Regulation will provide the backbone for supporting the space industry and will foster Europe’s space technological autonomy and resilience, to compete in the global race. It will also help the economy and society recover from the crisis resulting from the COVID-19 pandemic. Moreover, it will finance programs that leverage space for a stronger and more prosperous Europe in the years and decades to come for the EU citizens and businesses.
- The Regulation will be published in the Official Journal in the coming days, allowing it to enter into force the day of publication marking the first day of EUSPA. The Regulation will retroactively apply from 1 January 2021. Then, the Financial Framework Partnership Agreement (FFPA) and the relevant Contribution Agreements with the European Commission and ESA in order to implement the Regulation will be signed with the European Commission.
• April 18, 2021: Galileo: finding our way. 37)
Figure 22: More than two billion smartphones, with users worldwide are now making use of Europe's Galileo navigation satellite constellation. But how do satellites thousands of kilometers away in space manage to tell you where you are and where you're going? Simply being so far away is part of the answer - learn the details of the world's most precise navigation system in this new video (video credit: ESA)
• April 6, 2021: Today is 406 Day – the annual campaigning day to spread awareness of the importance of emergency beacons, and the satellites that pick up their signals, including Europe’s Galileo constellation. As well as letting people across the world find their way, Galileo also serves to detect SOS messages and relay them to authorities, contributing to saving many lives. 38)
- Such detections can happen anytime, but one recent high-profile incident happened in the midst of the Vendée Globe solo round-the-world yacht race. Skipper Kevin Escoffier had his boat smashed to pieces by fierce waves in the Southern Ocean.
Figure 23: Stranded sailors in liftraft use an emergency position-indicating radiobeacon (EPIRB) to call for help (image credit: GSA)
- He took to his life raft. As it hit the water it automatically activated his rescue beacon, transmitting a 406 MHz SOS signal for automatic pickup by participating satellites, courtesy of the Cospas-Sarsat satellite-based emergency detecting and locating system. The signal allowed the race authorities to localize Kevin’s position within a matter of minutes and send nearby boats to the rescue.
- The only system that can independently locate a beacon anywhere on Earth’s surface, Cospas-Sarsat has helped save thousands of people since it was first established in 1982. Originally the system operated through transponders hosted aboard either low-Earth orbit or geostationary satellites.
- In the last decade Galileo joined Cospas-Sarsat – supported by the European Commission, the system’s owner – driving a significant increase in performance. Because they have such a high orbital altitude, at 23,222 km up, while still moving steadily through the sky, Galileo satellites combine broad views of Earth with the ability to facilitate quick determination of the position of a distress signal through a combination of time-based and Doppler ranging.
- International 406 Day – taking its name from the radio frequency used by Cospas-Sarsat beacons, and the US order of today’s date – seeks to remind beacon users to take care to check their batteries and functionality. Such beacons are used aboard boats and ships, also aboard aircraft and are also carried by hikers in the wilderness – anywhere beyond the reach of standard phone-based emergency services.
Figure 24: For three decades the Cospas–Sarsat system has used relays on satellites such as Europe’s MSG and MetOp to pick up distress calls from ships and aircraft (image credit: Cospas-Sarsat)
- All the same, an SOS signal can reach the authorities surprisingly swiftly, within a few minutes. First the signal from the beacon is detected automatically by the search and rescue payload aboard participating satellites – often more than one at once – then pinpoints its source on Earth’s surface.
- Next, this information is relayed – via a set of stations on the corners of Europe, in the case of Galileo-detected signals – then passed to the nearest national rescue center, at which point the rescue can begin.
- The beacons themselves are surprisingly compact in size, typically the size of a medium-sized flashlight. But the search and rescue payloads carried aboard the Galileo satellites in orbit are similarly modest. At only 8 kg in mass, these life-saving payloads consume just 3% of onboard power, with their receive-transmit repeater housed next to the main navigation antenna.
Figure 25: Galileo satellites are placed in medium orbits, at 23,222 km altitude along three orbital planes so that a minimum of four satellites are visible to user receivers at any point on Earth. The satellites continuously broadcast navigation messages, allowing receivers to pinpoint their position. They also relay search and rescue messages received worldwide (image credit: ESA)
- All but the first two of the 26 Galileo satellites in orbit carry these payloads, with two more satellites scheduled to add to their number later this year.
- Galileo’s Search and Rescue service is Europe’s contribution to Cospas-Sarsat, operated by the European Global Navigation Satellite System Agency, GSA, and designed and developed at ESA.
- The Cospas-Sarsat satellite repeaters are supplemented by a trio of ground stations at the corners of Europe, known as Medium-Earth Orbit Local User Terminals (MEOLUTs), based in Norway’s Spitsbergen Islands, Cyprus and Spain’s Canary Islands and coordinated from a control centre in Toulouse, France.
- This trio is soon to become a quartet, with a fourth station on France's La Reunion Island in the Indian Ocean.
- Galileo’s participation in Cospas-Sarsat has led in turn to a service innovation – from last year, Galileo has been replying to SOS signals with ‘return link messages’, assuring those in peril that their signals have been received and help is on the way.
• March 10, 2021: In a first for any satellite navigation system, Galileo has achieved a positioning fix based on open-service navigation signals carrying authenticated data. Intended as a way to combat malicious ‘spoofing’ of satnav signals, this authentication testing began at ESA’s Navigation Laboratory – the same site where the very first Galileo positioning fix took place back in 2013. 39)
Figure 26: Signal testing. Satellites of all kinds have one central characteristic in common. They all have to reach out either to receive commands, transmit scientific findings, relay telecommunications, perform remote sensing or, increasingly, deliver precision navigation and timing data – relying on radio frequencies (RFs) to do so. ESA’s Radio Frequency Systems, Payload and Technology Laboratories perform RF research for both the space and ground segments. The main Lab is made up of five facilities: the General Microwave Lab, Radio Navigation Lab, Telecom Lab, Remote Sensing Lab and RF High-Power Lab (external), image credit: ESA
- These historic first authenticated signal ‘position, velocity, timing’ fixes were made using a total of eight Galileo satellites for around two hours on 18 November 2020. The tests represent a first proof of concept for an eventual operational service offering positioning with authenticated data to users.
- Spoofing has, for instance, been demonstrated as a means of forcing down drones or redirecting ships, while some high security locations – as well as disrupted international borders – have become notorious for spoofing signals that prevent the reliable use of satnav in their vicinity.
- “When a receiver picks up a navigation signal from a satellite, up until now it has no way of confirming that was indeed its source,” comments navigation engineer Stefano Binda, overseeing the project for ESA.
- “This can result in ‘spoofing’ – malicious people and organisations using false signals to mislead users about their actual position. This authentication service offers a way to prevent such deception.”
Figure 27: Satnav spoofing. Counterfeit satellite navigation signals can mislead user receivers on the ground, causing them to misidentify their position with potentially serious consequences. A new software suite called SimSAFE, developed by an Italian company called Qascom with ESA backing, allows prototype receivers to be tested and tuned against simulated spoofing attempts (image credit: Qascom)
- Stefano notes: “In recent years this problem has become sufficiently pronounced as a weak point that the European Commission, ESA and European GNSS Agency (GSA) decided to develop signal authentication as a differentiator for Galileo.”
- An ESA Navigation Directorate team at the Agency’s ESTEC technical centre in the Netherlands worked with their GSA counterparts at the twin Galileo Control Centers (GCCs) in Italy and Germany and the Galileo Service Centre (GSC) in Spain.
- “In everyday authentication you might send a document that has been digitally signed, where both sender and recipient use compatible cryptographic keys to validate the document’s source of origin,” adds Stefano.
Figure 28: Drones can be downed by spoofing. INVOLI drone. ESA BIC Switzerland start-up INVOLI provides a solution to increase air traffic awareness on existing drone systems, without modifying the drone’s hardware. Meet INVOLI at the 10th ESA Investment Forum in ESOC 31 January 2019 (image credit: INVOLI)
- “In everyday authentication you might send a document that has been digitally signed, where both sender and recipient use compatible cryptographic keys to validate the document’s source of origin,” adds Stefano.
- “In this case we were working with a constrained amount of bandwidth within the navigation signal, so instead opted for a ‘delayed key’ approach. This means the initial data come along together a short tag which, within a short stretch of time usually not exceeding 30 seconds, is followed by a key, which is able to validate the tag and authenticate the data associated with it.”
- During the test campaign, the Galileo Control Centers send the navigation signal to the GSC for the addition of the authentication code, which is then returned for uplink to the satellites, to be received and authenticated by the test receivers at ESTEC’s Navigation Lab and elsewhere in Europe, in participating laboratories.
- To enable the authentication test campaign, Thales Alenia Space in France served as prime contractor to upgrade of the ‘Galileo Mission Segment’ – the world-spanning system that determines and create the navigation messages broadcast by Galileo satellites. Thales Alenia Space in Italy was responsible for the system level integration. No modification of onboard satellite systems has been required to support Open Service Navigation Message Authentication (OS NMA), as spare bandwidth was made use of.
- “We used our standard laboratory Septentrio test user receivers with a software add-on,” comments Stefano. “The beauty of this approach is that receivers will be able to make use of the future authenticated service without needing any new hardware, only software updates – apart from additional measures that might be mandated for operation in practice.”
- ESA and GSA are continuing their authentication testing, with a view to introducing an operational Open Service Navigation Message Authentication service for users in the near future.
Figure 29: Open Service Navigation Message Authentication (image credit: ESA)
• January 11, 2021: The end of 2020 marked a notable milestone for Europe’s Galileo First Generation, as the program chalked up its 500th ESA Engineering Board. 40)
Figure 30: Circular L-band (navigation) and hexagonal (SAR) antenna (image credit: Galileo GNSS)
- Since the first such ‘G1’ Engineering Board in 2008 a total of 26 Galileo satellites have been built, tested and flown, with a further 12 ‘Batch 3’ satellites set to join them in orbit during the coming decade – these satellites are currently being finalized at OHB Systems in Bremen, Germany, then tested at ESA’s ESTEC Test Centre in the Netherlands.
- The Galileo system’s globe-spanning ground system has also been put in place and made operational. Galileo began initial operations in December 2016 and is today the world’s single most accurate satellite navigation system, serving more than 1.5 billion smartphones and devices. But all that effort owes its origins to the regular sequence of G1 Engineering Boards.
- Much like a modern version of the Agora public square of ancient Greece, Galileo’s ESA Engineering Board is the forum where technical experts regularly meet with a clear objective: maintaining, reviewing and updating the Galileo Project technical baseline, the STRB (System Technical Requirements Baseline).
- This STRB drives the implementation of the Galileo System and its infrastructure, namely the space and ground segments, along with associated interfaces and operations. All in all, the G1 system technical specification under ESA responsibility adds up to more than 22,000 separate requirements – both unclassified and classified in nature, with considerable interdependencies which all need to be controlled in configuration.
- The Galileo G1 Engineering Board is chaired by ESA in accordance with its role as Galileo System Design Authority, assigned to it by the European Commission.
- For more than 12 years now, ESA and industry engineers from all relevant disciplines – covering system, satellite, ground, signal, radio-navigation, RAMS (reliability, availability, maintainability and safety), security and infrastructure – have put their best skills at the disposal of this Board. It continues to be a crucial enabler for further robustness improvements and new service evolutions.
- The G1 Engineering Board meetings will continue into the future, complemented with the Engineering Boards for the new Galileo Second Generation (G2 satellites are planned for later this decade) which are already well underway.
• August 14, 2020: With 26 satellites now in orbit and over 1.5 billion smartphones and devices worldwide receiving highly accurate navigation signals, Europe’s Galileo navigation system will soon become even better, ensuring quality services over the next decades. 41)
- Following the European Commission’s decision to accelerate development of Galileo Next Generation, ESA has asked European satellite manufacturers to submit bids for the first batch of the Galileo Second Generation (G2) satellites. The new spacecraft are expected to be launched in about four years.
- The next-generation satellites will provide all the services and capabilities of the current first generation, together with a substantial number of improvements as well as new services and capabilities.
- “We want an ultra-flexible and mostly digital design,” says Paul Verhoef, ESA Director of Navigation.
- “Developing the second generation is challenging for both industry and for ESA. In 2024, we need to launch the first satellites for this new state-of-the-art constellation.”
Industry steps up
- Following almost 24 months of a competitive dialog procedure with the three large system integrators involved, ESA issued a so-called ‘Best and Final Offer’ invitation to tender on 11 August to Airbus, OHB System AG and Thales Alenia Space.
- ESA is implementing a dual-sourcing approach, and two parallel contracts are expected to be signed around the end of 2020 amongst the current three bidders. Under the plan, each of the two selectees will build two satellites for development purposes, with options for up to 12 satellites in total.
- The first satellites of the new constellation are foreseen for launch before the end of 2024, together with updated ground systems to support the new satellites.
New, improved and revolutionary
- In addition to being more powerful, the second-generation Galileo satellites will be more flexible, able to be reconfigured in orbit in order to satisfy the expected evolution in end-user needs.
- A number of challenges exist for the bidders, as the goal of a digital and fully flexible design represents the cutting edge of industrial capability. Furthermore, the required navigation antennas, the ones that transmit the actual navigation signals to smartphones and other receivers on ground, have a very advanced design, and quite a lot of research and development work by ESA has been done and remains for industry.
- ESA has already built such an antenna as a proof of concept at the Agency’s ESTEC technology center in the Netherlands to ensure feasibility, and the know-how has been shared with the three bidders.
- “Each bidder must determine how they can best manufacture the navigation antenna, and we’ll have to see how each proposes to do it. Also, requiring a fully flexible payload is quite a challenge. No such navigation spacecraft of that type have flown yet,” says Verhoef.
Transitioning into the future
- The European Commission has decided that what was previously going to be called the ‘transition batch’ of new satellites will now become, in fact, the Galileo Second Generation satellites. The European Commission and EU Member States have already made clear that they want to be very ambitious and further increase the technical capabilities of the Galileo system. The change of name recognizes the reality of how the current batch are actually shaping up.
- The transition satellites were initially foreseen as interim upgrades, to cater for the potential risk of late delivery of the later, completely new and very advanced G2 satellites.
- Based on constant measurements of the performance of the current satellites in orbit, their predicted lifetime has increased. So, together with a slight spreading out the launches of the so-called 'Batch 3' satellites, which are currently under construction by OHB and in testing at ESTEC, this will ensure service continuity before the new, advanced capabilities of Galileo come into operation.
- These second generation satellites will gradually take over from the current first generation satellites in the provision of Galileo services, and will therefore at a future date constitute a complete constellation plus the necessary in-orbit spares.
- ESA serves as the design, development and procurement agent for Galileo satellites on behalf of the European Commission, which funds the system overall.
GIDAS (GNSS Interference Detection and Analysis System)
• July 20, 2020: A new monitoring system developed through an ESA-backed project works like a ‘bodyguard’ for satellite navigation in use at strategic or safety-critical sites. Known as GIDAS, the scalable system immediately detects, identifies and pinpoints satnav interference sources in its vicinity. 42)
It is estimated that there are currently the same number of satnav receivers on Earth as there are people. Positioning, navigation and timing signals from space-based constellations such as Galileo and GPS form an invisible, essential infrastructure, underpinning numerous modern aspects of modern life: communications, power and transportation.
Satellite navigation helps guide a growing number of aircraft, boats, trains and autonomous vehicles. Meanwhile satnav-based time-stamps authentic multi-billion euro financial transactions, and coordinate the synchronized running of power grids. Satellite navigation is always on, available everywhere on Earth, so it is easy to take its availability for granted. But as crucial as these signals from space are, they are also vulnerable to ground-based interference.
“It’s simply a matter of output power,” says Andreas Lesch of Austria-based OHB Digital Solutions. “A navigation signal on the ground is equivalent to the light from a 60 watt lamp aboard a satellite, some 23,222 km in altitude away in space in the case of Galileo. So these faint signals can be jammed by more powerful local radio signals, either accidentally or deliberately, or even misleading fake navigation signals, known as ‘spoofing’.
“The company initiated the project through NAVISP’s second element, focused on strengthening European competitiveness in the navigation arena, proceeding on a co-funded basis,”says engineer Thomas Burger, overseeing GIDAS project for ESA. “The plan was to enable a commercially attractive business to get started, and I’m happy to say we made it.”
Figure 31: Surveying using satnav with EGNOS and Galileo satellites [image credit: GSA (GNSS Supervisory Agency), Europe]
Our new GIDAS (GNSS Interference Detection and Analysis System) is designed to safeguard critical infrastructure against jamming or spoofing, by performing continuous monitoring of key signal bands. By doing so, GIDAS can raise the alarm in realtime, identify the type of interference then pinpoint the location of these dangerous portable devices causing the interference so the authorities can take immediate remedial action.”
GIDAS can provide interference detection and directionality with a single reporting station, although a minimum of three stations are required for pinpointing interference sources, linked to an overall monitoring center. Monitoring centers can also be connected together, making the GIDAS system easily scalable, from safeguarding an individual harbor, airport or system critical site up to an entire city or region.
Figure 32: Safeguarding satnav (image credit: OHB Digital Solutions)
“People are only now catching up to the seriousness of this problem,” adds Andreas. “Surveys of the highest-density parts of Europe surveys report around three to four jammers hourly.
Figure 33: GIDAS reporting station. GIDAS can provide interference detection and directionality with a single reporting station, although a minimum of three stations are required for pinpointing interference sources, linked to an overall monitoring center (image credit: OHB Digital Solutions)
“These small devices are technically illegal but are easily available online for a few hundred euros or less, often marketed as ‘personal privacy devices’. Jammers are sold as having a range of only a few meters, but can turn out to have a practical range of dozens of meters or more – leading to unintentionally widespread interference, like the famous jammer-equipped US truck driver who shut down Newark Airport navigation systems whenever he drove past.
Figure 34: Jamming devices are technically illegal but are easily available online for a few hundred euros or less, often marketed as ‘personal privacy devices’. Jammers are sold as having a range of only a few meters, but can turn out to have a practical range of dozens of meters or more – leading to unintentionally widespread interference (image credit: OHB Digital Solutions)
“Spoofing is more serious still, with a strong criminal element, where false satellite navigation signals replace real ones, to mislead receivers about their position, employed in the past to down put drones or divert boats.
“Working in this field for eight to nine years, we have seen a strong growth in interference, even as GNSS becomes ever more crucial. With our passion for GNSS and signal processing, we decided to something practical to combat this development, delivering rapid detection, classification and localization of interference to our customers.”
GIDAS was developed by OHB Digital Solutions and Joanneum University through ESA’s Navigation Innovation and Support Program (NAVISP), working with European industry and academia to develop innovative navigation technology.
“The company initiated the project through NAVISP’s second element, focused on strengthening European competitiveness in the navigation arena, proceeding on a co-funded basis,”says engineer Thomas Burger, overseeing GIDAS project for ESA. “The plan was to enable a commercially attractive business to get started, and I’m happy to say we made it.”
“Considering the budget, the project had a wide scope, including the development of a multi-constellation GNSS receiver with all processing stages, an extended digital front end for jamming and spoofing detection, processing blocks transferred to a parallel processor based on a customized fully programmable gate array.
Figure 35: GIDAS dashboard. The new GIDAS is designed to safeguard satnav-reliant critical infrastructure against jamming or spoofing, by performing continuous monitoring of key signal bands. By doing so, GIDAS can raise the alarm in realtime, identify the type of interference then pinpoint the location of these dangerous portable devices causing the interference so the authorities can take immediate remedial action (image credit: OHB Digital Solutions)
“And that was only one ingredient of the overall GIDAS system, also including the actual interference detection machinery, the interference locating subsystem, and all the communication, database, and graphical user interface elements needed to create a distributed, human-usable system – which is able to go on working autonomously, only asking for human involvement when events are detected.”
Following the conclusion of the two-year NAVISP project, GIDAS is now in the process of being rolled out to several Europe-based governmental and private sector customers.
Figure 36: Pinpointing interference (image credit: OHB Digital Solutions)
Figure 37: OHB Digital Solutions GmbH develops systems for monitoring the GNSS frequency bands as well as detection, classification and localization of intentional or unintentional interference sources (video credit: OHB Digital Solutions GmbH)
• April 29, 2020: As European governments plan their phased recoveries from the lockdown states triggered by the COVID-19 pandemic, the positioning delivered through satellite navigation is becoming more important than ever before. Location is a key requirement when attempting to monitor and map the spread of a disease and satnav is one of the main tools supporting this. 43)
- Since the outbreak of the coronavirus earlier this year, many apps have been developed that use satnav-based location data to monitor the global spread of the virus and to map outbreaks of the COVID-19 disease. Satnav based apps are also proving their usefulness by helping people to implement social distancing in queues and other public spaces.
- The Romanian company RISE has developed an app called CovTrack, which monitors people in your vicinity made identifiable via Bluetooth connections to your mobile phone and stores the identification data of these devices.
- By pressing a button you can access the database in which the unique identifiers of the mobile phones are registered (without having access to any personal data of these mobile phone users), to verify whether the persons with whom you came in contact have subsequently been confirmed with COVID-19. If you have identified a potential contact, you can refer to the relevant authorities whether that contact requires your inclusion among the monitored persons, or even testing for COVID-19.
Figure 38: CovTrack Infographic - HD. CovTrack, developed on a pro-bono basis, is a spin-off from the existing AGORA project for festival management, supported through ESA’s Navigation Innovation and Support Program (NAVISP), focused on future navigation technologies (video credit: ESA)
- ESA’s partner agency the GSA, European Global Navigation Satellite System Agency, working with the assistance of the European Commission, has put together a repository of such apps, available here.
- This list, based on apps that are already working and available in app stores, includes practical apps that facilitate the daily lives of citizens, such as by helping them to manage queues in supermarkets, pharmacies and public spaces or by facilitating the logistics of goods, which has become more complicated in the current situation.
- Europe’s Galileo, currently embedded in over 1.3 billion smartphones and devices worldwide, is helping to increase satnav accuracy and availability, especially in urban areas. Is your own smartphone or device making use of Galileo, the most accurate satnav system? You can check here.
- The GSA is also developing its own Galileo-enabled application, Galileo for Green Lane, to monitor and ease the circulation of goods between EU Member States while identifying potential congestion at Green Lane border crossings, and thus ensuring that EU citizens can access the needed supplies of critical goods.
• February 14, 2020: Eutelsat Communications has informed all that the GEO-3 payload of the European Geostationary Navigation Overlay System (EGNOS), a hosted payload aboard the company's EUTELSAT 5 West B satellite, has successfully entered into service. 44)
- EUTELSAT 5 West B is hosting the Eutelsat-procured EGNOS payload under a 15-year agreement that was signed in 2017 with the European Global Navigation Satellite Systems Agency (GSA). The contract also includes technical services and a European ground infrastructure, including two gateways installed at Eutelsat’s Rambouillet and Cagliari teleports.
- Yohann Leroy, Eutelsat’s Deputy CEO and Chief Technical Officer, said that the firm is proud of the collaboration with customer GSA, its partners including the European Space Agency (ESA), and its suppliers, culminating in the entry into service of this next generation technology of EGNOS on EUTELSAT 5 West B. Eutelsat is delighted to host this payload, which will significantly enhance the performance of global navigation satellite systems across Europe, notably Galileo, in the coming years.
- Pascal Claudel, GSA Acting Executive Director and COO, added that with this new payload in service, EGNOS is moving toward the transition to its new generation. This has been done thanks to the constructive collaboration with Eutelsat. Delivery and continuity of satellite services are part of the company's mission as delegated by the European Commission. It is essential that the GSA ensures these services to support economic growth and that the European Union’s citizens and companies can benefit from the latest GNSS technology.
• January 23, 2020: As well as providing global navigation services, Europe’s Galileo satellite constellation is contributing to saving more than 2000 lives annually by relaying SOS messages to first responders. And from now on the satellites will reply to these messages, assuring people in danger that help is on the way. 45)
- This ESA-design ‘return link’ system, unique to Galileo, was declared operational this week, during the 12th European Space Conference in Belgium. The delivery time for the return link acknowledgement messages from initial emergency beacon activation is expected to be a couple of minutes in the majority of cases, up to 30 minutes maximum, depending primarily on the time it takes to detect and locate the alert.
- “Anyone in trouble will now receive solid confirmation, through an indication on their activated beacon, informing them that search and rescue services have been informed of their alert and location,” explains ESA’s Galileo principal search and rescue engineer Igor Stojkovic. “For anyone in a tough situation, such knowledge could make a big difference.”
- All but the first two out of 26 Galileo satellites carry a Cospas-Sarsat search and rescue package. At only 8 kg in mass, these life-saving payloads consume just 3% of onboard power, with their receive-transmit repeater housed next to the main navigation antenna.
- Founded by Canada, France, Russia and the US in 1979, Cospas-Sarsat began with payloads on LEO (Low Earth Orbiting) satellites, whose rapid orbital motion allows Doppler ranging of distress signals, to pinpoint their location. The drawback is these fly so close to Earth that their field of view is comparatively small.
- GEO (Geostationary Earth Orbiting) satellites went on to host Cospas-Sarsat payloads. These see much more of the planet, but because they are motionless relative to Earth’s surface, Doppler ranging is not possible.
- MEO (Medium Earth Orbiting) satellites such as Galileo – orbiting at 23,222 km altitude – offer the best of both worlds, providing a wide ground view by multiple satellites combined with time-of-arrival and Doppler ranging techniques to localize SOS signals. This improves the maximum signal detection time from four hours to less than five minutes, down to 1 or 2 km (within a formal specification of 5 km within 10 minutes).
- Galileo’s Search and Rescue service is Europe’s contribution to Cospas-Sarsat, operated by the European GSA (Global Navigation Satellite System Agency), and designed and developed at ESA. As the overall Galileo system architect and design authority, ESA has been responsible for the interface between the core Galileo infrastructure to the Return Link Service Provider facility, procured by the European Commission and operated by French space agency CNES.
- The Cospas-Sarsat satellite repeaters are supplemented by a trio of ground stations at the corners of Europe, known as Medium-Earth Orbit Local User Terminals (MEOLUTs), based in Norway’s Spitsbergen Islands, Cyprus and Spain’s Canary Islands and coordinated from a control center in Toulouse, France. This trio is soon to become a quartet, with a fourth station on France's La Reunion Island in the Indian Ocean under development.
- The satellites relay distress messages to these MEOLUTs, which then relay them to local search and rescue authorities.
- The service’s return link message capability was developed as an inherent part of the Galileo system. The messages are relayed to the individual beacons that sent the original distress call by being embedded within Galileo signals broadcast from satellites in their view.
- “The switching on of the return link service was enabled by a thorough test campaign carried out by ESA, with the support of the GSA and CNES,” adds Igor. “We needed to be sure the service remains reliable even with multiple distress calls being replied to at once.”
- A key milestone was a public demonstration of the return link service, performed at the Cospas-Sarsat Joint Committee Meeting in Doha in Qatar last summer.
- “The return link is a joint service of Cospas-Sarsat and Galileo and therefore agreement by Cospas-Sarsat was crucial,” adds Igor.
- “This acceptance was achieved through long discussions led by the European Commission at the Cospas-Sarsat Council last November, supported by plentiful documentation of simulations and test results provided by ESA and CNES.”
Figure 39: GALILEO : Reaching you faster – when every minute matters. Search and Rescue (SAR) operations involve locating and helping people in distress. They can be carried out in a variety of locations including at sea, in mountains or deserts, and in urban areas. With the launch of Initial Services, Galileo will help SAR operators respond to distress signals faster and more effectively while also lowering their own exposure to risk ... (video credit: European Commission)
Note: This 'Mission Status' entry of January 23, 2020 is repeated below at Status of Galileo's SAR (Search & Rescue) Service.
• December 20, 2019: The Galileo satellite navigation system has been providing Initial Services for three years now. Meanwhile Europe’s other satnav system has marked its tenth anniversary: EGNOS has been delivering enhanced positioning to users across our continent, including safety-critical services such as aircraft landings for a growing number of European airports. 46)
- The purpose of EGNOS (European Geostationary Navigation Overlay Service) is to monitor the real-time performance of US GPS satellites, then generate a correction message, containing information on the reliability and accuracy of their positioning data, which are then broadcast via EGNOS’s geostationary satellites to all suitably equipped satnav receivers.
Figure 40: The purpose of EGNOS is to monitor the real-time performance of US GPS satellites, then generate a correction message, containing information on the reliability and accuracy of their positioning data, which are then broadcast via EGNOS’s geostationary satellites to all suitably equipped satnav receivers. EGNOS consists of three geostationary satellites and a Europe-wide ground segment composed of two master control stations, six uplink stations and a network of 40 monitoring stations, all connected and communicating in real time (image credit: ESA)
- The end result is a several-fold increase in positioning accuracy and reliability – which is expressed for aviation users through the notion of its ‘integrity’ – how much can it relied upon at any given time. EGNOS typically allows users in Europe and beyond to determine their position to within 1.5 meters with a very high level of integrity, allowing aircraft to be safely guided down to airport runways.
- EGNOS consists of three geostationary satellites and a Europe-wide ground segment composed of two master control stations, six uplink stations and a network of 40 monitoring stations, all connected and communicating in real time.
- EGNOS was a joint project of ESA, the European Commission and Eurocontrol, the European Organisation for the Safety of Air Navigation. The system’s Open Service began on 1 October 2009, after which EGNOS positioning data became freely available in Europe through satellite signals to anyone equipped with an EGNOS-enabled GPS receiver.
- The system is employed for accuracy and integrity-hungry satnav applications such as precision farming, surveying and transport. EGNOS is, for instance, used within the new eCall system, found in all new cars sold in the EU since March 2018. Whenever a serious accident occurs, eCall automatically passes the incident location to the emergency services, with EGNOS providing added accuracy and integrity.
Figure 41: EGNOS for precision farming. EGNOS is employed for accuracy and integrity-hungry satnav applications such as precision farming, surveying and transport (image credit: GSA)
- But as the European equivalent of the US Wide Area Augmentation System WAAS, EGNOS was primarily designed to serve aviation, specifically for the safety-critical task of guiding down aircraft for landings. This became possible on 2 March 2011, when EGNOS’s ‘Safety-of-Life’ service began to operate.
- Today more than 350 airports - more than half of the total – across Europe employ EGNOS. To do so, they have been certified for what are known as ‘LPV-200 procedures’ allowing pilots to take their aircraft down to 60 m (200 ft) above the ground for a final go/no-go decision on continued landing descent. LPV stands for ‘localizer performance with vertical guidance’.
- This certification allows airports to operate without costly ground-based Instrument Landing System ‘Cat-1’ infrastructure. Major airports hubs such as Paris Charles de Gaulle, Frankfurt and Amsterdam Schiphol employ EGNOS for landing approaches. For smaller regional airports, EGNOS allows them to stay open in all weathers.
Figure 42: Aircraft pilots are making use of EGNOS for what are known as ‘approach with vertical guidance’ procedures at suitably certified European airports. They can provide vertical guidance down to within 60 m altitude of given runways in all weather and conditions, at which point the pilot does the rest (image credit: GSA)
Figure 43: As of April 2018 all new cars will be equipped with eCall technology. In the event of a serious accident, eCall automatically dials 112 - Europe's single emergency number - to provide faster assistance and save lives (video credit: GSA)
- The EGNOS Exploitation Program is managed by the European Global Navigation Satellite System Agency, GSA. ESA retains the role of developing its future System evolution, taking shape as ‘EGNOS V3’ in the coming decade, which will augment signals from both GPS and Galileo satellites for added performance, reliability and extended coverage.
Figure 44: EGNOS augmenting satellite navigation (video credit: ESA)
• July 22, 2019: The Initial Services provided by the European satellite navigation system - Galileo - have been successfully restored. Galileo was affected by a technical incident related to its ground infrastructure. This event led to a temporary interruption of the globally available Galileo navigation and timing services, with the exception of the Galileo Search and Rescue Service. 47)
- The Search and Rescue Service, which is used to locate and assist people in emergency situations, for example, at sea or in remote, mountainous areas, was not affected and remained operational.
- The navigation service impact was caused by a malfunction of some equipment in the Galileo control centers, which generate the system time and calculate orbit predictions; these data are used to produce the navigation messages. The disruption affected various elements at the control centers in Fucino (Italy) and at the DLR site in Oberpfaffenhofen.
- A team of experts from the Galileo Service Operator, led by Spaceopal GmbH, worked as quickly as possible and in close cooperation with the European GNSS Agency (GSA), as well as the industrial ground infrastructure providers together with the European Space Agency (ESA) to rectify the malfunction.
- Due to the high technical complexity of the system and the in-depth analysis of the fault dependencies, these efforts took several days before the resumption of Initial Services on 18 July 2018.
- An independent board of inquiry is now investigating the exact circumstances and root causes that led to the failure. The investigation is being conducted by the EU Commission and the GSA - the authorities that manage the program - in order to continuously improve the system during its initial service phase.
- Galileo has been offering its Initial Service since December 2016. During this initial 'pilot' phase, which precedes the 'full-operational services' phase, Galileo signals are being used also in combination with those from other satellite navigation systems, allowing testing and the detection of potential technical challenges during the commissioning of the system until full deployment and operational capability has been reached.
• July 18, 2019: Galileo Initial Services have now been restored. Commercial users can already see signs of recovery of the Galileo navigation and timing services, although some fluctuations may be experienced until further notice. 48)
- The technical incident originated by an equipment malfunction in the Galileo control centers that calculate time and orbit predictions, and which are used to compute the navigation message. The malfunction affected different elements on both centers.
- A team composed of GSA (Global Navigation Satellite Systems Agency) experts, industry, ESA and Commission, worked together 24/7 to address the incident. The team is monitoring the quality of Galileo services to restore Galileo timing and navigation services at their nominal levels.
- We will set an Independent Inquiry Board to identify the root causes of the major incident. This will allow the Commission, as the program manager, together with the EU Agency GSA to draw lessons for the management of an operational system with several millions of users worldwide.
- Galileo provides ‘initial services’ since December 2016. During this initial ‘pilot’ phase preceding the ‘full operational services’ phase, Galileo signals are used in combination with other satellite navigation systems, which allows for the detection of technical issues before the system becomes fully operational. In the full operational phase, Galileo should function independently of other satellite navigation systems.
• July 17, 2019: A team of experts from the European GNSS Agency, industry, the European Space Agency and the European Commission is currently implementing and monitoring recovery actions for an incident related to the Galileo ground infrastructure that resulted in a temporary interruption of the Galileo Initial Services. The key objective is to restore the Galileo navigation and timing services for users as soon as possible. 49)
- On 12 July, Galileo initial navigation and timing services were interrupted temporarily. The Galileo Search and Rescue service remains operational.
- Galileo is widely used by most of the commercially available receivers. Multi-constellation GNSS receivers will remain unaffected and compute position and timing using other constellations. Galileo-only receivers will not produce any navigation message.
- As soon as the incident was declared, an Anomaly Review Board was convened and urgent recovery procedures were activated in the affected Galileo infrastructures. Operational teams are working on recovery actions 24/7 to restore the Galileo navigation and timing services as soon as possible.
- Based on the results of the troubleshooting activities, several elements of the ground infrastructure were re-initiated. The progress is being closely monitored; it is too early to confirm an exact service recovery date.
A period for testing and perfecting
- The Galileo satellite navigation system launched its Initial Services in December 2016 and since then it has been providing high quality positioning, navigation and timing services to users worldwide. The aim of this Initial Services phase is to allow for the detection of technical issues before the system becomes fully operational.
- It was precisely to deal with issues of this nature that the EU opted for a progressive roll-out of the Galileo system. The evolution and planned upgrade of the ground infrastructure will reinforce redundancy of the system towards reaching the full operations phase.
- As soon as the outage occurred, the users were informed by the Galileo Service Center through technical notices on 11 and 13 July , as well as a news item on the GSA website on 14 July. Users will be regularly updated, including on the navigation and timing service recovery date, through notifications and information.
- The Galileo team would like to assure users that it is working hard to remedy the situation as soon as possible.
• July 14, 2019: Galileo, the EU's satellite navigation system, is currently affected by a technical incident related to its ground infrastructure. The incident has led to a temporary interruption of the Galileo initial navigation and timing services, with the exception of the Galileo Search and Rescue (SAR) service. The SAR service - used for locating and helping people in distress situations for example at sea or mountains - is unaffected and remains operational. 50)
- Galileo provides ‘initial services’ since December 2016. During this initial "pilot" phase preceding the ‘full operational services’ phase, Galileo signals are used in combination with other satellite navigation systems, which allows for the detection of technical issues before the system becomes fully operational.
- Experts are working to restore the situation as soon as possible. An Anomaly Review Board has been immediately set up to analyze the exact root cause and to implement recovery actions.
- As foreseen in case of technical incidents, information Notices to Galileo Users (NAGU) were already published on the Galileo Service Center website:
a) on 11 July 2019: https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2019025
b) and on 13 July 2019 : https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2019026
- Users will be informed regularly, including on the service recovery date.
• June 11, 2019: Europe’s students and young researchers were challenged to design a smartphone app to take advantage of Galileo’s dual-frequency signals. Run by ESA in collaboration with the European Global Navigation Satellite Systems Agency – GSA – plus the European Commission with the support of Google, a total of five teams made it to the final of the Galileo smartphone app competition 2019 which took place at ESA’s ESTEC technical heart in the Netherlands on Thursday 18 April. This event was preceded by testing the performance of the competing apps in static, pedestrian and driving use modes. 51)
Figure 45: We are Europe's gateway to space. Our mission is to shape the development of Europe's space capability and ensure that investment in space continues to deliver benefits to the citizens of Europe and the world (video credit: ESA, Uploaded on 11 June 2019)
• March 4, 2019: Global leader in emergency readiness and response, Orolia, is pleased to announce that its McMurdo FastFind 220 and Kannad SafeLink Solo PLBs (Personal Location Beacons) now operate with the Galileo GNSS system. 52)
- Continuing Orolia's innovation and leadership role in Safety Electronics, the PLBs have been upgraded to include Galileo Global Navigation Satellite System (GNSS), the European Union's global satellite constellation.
Figure 46: These are the world's first PLBs utilizing the Galileo satellites' capabilities and are the first of a series of new solutions coming from the EU-funded Helios project, led by Orolia, which has been set up to leverage the power of the new satellite system (image credit: Orolia)
- The multi-constellation receivers work with a wider range of satellites, offering increased global coverage and supporting accelerated rescue missions.
- Location detection is enhanced and can be more precise due to the beacons receiving coordinates from the Galileo satellite network in addition to the tried and tested GPS network. Signals can even be detected in high sided locations, such as canyons.
- "We are thrilled to be launching our upgraded PLBs in the European and US markets," said Chris Loizou, Vice President of Maritime at Orolia.
- "The combination of both Galileo and GPS GNSS capability means that our customers will benefit from coverage that spans from the North to the South Pole. We work tirelessly to push the boundaries of product innovation and, ultimately, to give people the best chance of being rescued in an emergency situation."
- The McMurdo FastFind and Kannad SafeLink PLBs are part of Orolia's comprehensive search and rescue ecosystem and join the McMurdo SmartFind G8 and Kannad SafePro series EPIRBs (Emergency Position Indicating Radio Beacons) as the first Galileo capable rescue beacons.
- As the world's only provider of an end-to-end search and rescue ecosystem - including distress beacons, satellite ground stations, mission control and rescue coordination systems, and rescue response products - Orolia's McMurdo brand uniquely builds, integrates and tests products as part of a live search and rescue system.
- This ensures greater cohesion between distress signal transmission and reception so that beacon owners can feel confident that their signals will get to search and rescue authorities quickly.
• February 7, 2019: The latest four Galileo satellites, launched on 25 July 2018, have been given the green light to begin working alongside the rest of Europe’s satellite navigation fleet, giving a further boost to worldwide Galileo service quality. 53)
- Galileo has grown to become Europe’s single largest satellite constellation, built up over 10 launches over the course of this decade. The first of seven double-satellite Soyuz launches took place in 2011, with three sets of four-satellite Ariane-5 launches during the last three years. — The latest quartet of Galileo satellites were launched together by Ariane 5 on 25 July, bringing the number of satellites in orbit to 26.
Figure 47: Europe's Galileo navigation satellites orbit 23 222 km above Earth to provide positioning, navigation and timing information all across the globe (image credit: GSA)
• December 17, 2018: Use Europe’s satellite navigation system to seek treasure in virtual mazes or ‘see’ Galileos as they cross the sky above you: two new Android smartphone apps based on Galileo are now available for general download, the results of a competition by ESA trainees. 54)
- With newer Android smartphones you can access the raw signal measurements used to compute position, opening the door to the development of applications where the user can indeed select which satellites to use. So ESA ran an internal competition for its trainees to develop an app capable of making positioning fixes using only Galileo satellites.
- The Callisto – Galileo’s Spaceship app uses Galileo satnav signals to run a virtual maze game based on walking through a real world location.
- Looking down on Earth as if from a spaceship, players use a standard Google map display to traverse a rectangular area filled with randomly generated obstacles and collectibles. You play against the clock to grab prizes, with points deducted for running into virtual barriers.
- “It was fun for us to develop as a team, but one of the main purposes behind it was to spread the message about Galileo,” explains ESA young graduate trainee Peter Vanik, part of the five-person ‘Chocolateam’ that created the app.
- “Users can use signals from the Galileo constellation by itself, GPS by itself or GPS and Galileo in combination to get a sense of the different accuracy levels – the combination of constellations will work best, because that way the most satellites are available for use.”
- The team used online tutorials and YouTube videos to learn how to develop for Android, with their satnav backend derived from GNSSCompare – the winning app from ESA’s internal competition, offering to turn a smartphone in a ‘research lab in your pocket’.
- None of us are satnav specialists, so we played off not knowing all the nitty-gritty as an advantage rather than a weakness, in terms of targeting the general public,” adds Matej Poliaček of the Callisto team.
- “The idea of a game came up early on, with a satnav-based gameplay loop,” says the team’s Cedric Ia. “Then Lionel Garcia, our designer, had the idea of making it spaceship-based, and that was where the design for our user interface came from.”
- “Working together with GNSSCompare was a way to combine the best of both worlds,” explains team member Emilie Udnæs. “They’re stronger on the GNSS side of things while we took a user-centered approach.
- The Callisto app was designed on and for a Galaxy S8 smartphone, but the team is expanding the app to serve as many different phones as possible, to target a general public audience.
- Another app developed through the competition is also available for download from Google Play. GalileoPVT was created by ESA navigation engineer Paola Crosta and electrical engineer Tim Watterton to serve as a benchmark to judge competition entries. The duo went on to finalize and publish it.
- “GalileoPVT allows users to compare position fixes calculated from Galileo and GPS signals, and also to visualize Galileo satellites and signals live in the sky using augmented reality,” explains Tim.
- “The raw signals can be saved for post-processing by users. There’s also a fun hidden game, where the player has to maneuver their Galileo satellite to avoid increasingly bizarre items of space debris, aided by received Galileo signals that boost their satellite’s health.”
- “GalileoPVT can also be installed on devices that do not support Galileo signals. Although the user will not be able to receive the live Galileo signals or calculate a fix with Galileo, they can still see the predicted satellite positions on the augmented reality view, and play the hidden game.”
- A current list of smartphones that support Galileo can be found here.
Figure 48: The GalileoPVT app allows users to compare position fixes calculated from Galileo and GPS signals, and also to visualize Galileo satellites and signals live in the sky using augmented reality. It also features a hidden game (image credit: ESA)
Figure 49: An augmented reality view of a Galileo satellite above Cape Town, South Africa. Space engineer Frank Bagiana took a smartphone equipped with the GalileoPVT app during his holiday to Africa to take some pictures of Europe's navigation satellites. Satellites in green are contributing to the receiver's positioning solution (image credit: ESA)
• December 4, 2018: Galileo satellites measure Einsteinian Time Dilation. Europe’s Galileo satellite navigation system – already serving users globally – has now provided a historic service to the physics community worldwide, enabling the most accurate measurement ever made of how shifts in gravity alter the passing of time, a key element of Einstein’s Theory of General Relativity. 55)
Two European fundamental physics teams working in parallel have independently achieved about a fivefold improvement in measuring accuracy of the gravity-driven time dilation effect known as ‘gravitational redshift’.
The prestigious Physical Review Letters journal has just published the independent results obtained from both consortiums, gathered from more than a thousand days of data obtained from the pair of Galileo satellites in elongated orbits. 56)
Figure 50: The relativistic eccentricity of Galileo satellites 5 and 6 reaches a peak amplitude of approximately 370 nanoseconds (billionths of a second), driven by the shifting altitude, and hence changing gravity levels, of their elliptical orbits around Earth. A periodic modulation of this size is clearly discernible, given the relative frequency stability of the PHM (Passive Hydrogen Maser) atomic clocks aboard the satellites (image credit: ESA)
It is most satisfying for ESA to see that our original expectation that such results might be theoretically possible have now been borne out in practical terms, providing the first reported improvement of the gravitational redshift test for more than 40 years,” comments Javier Ventura-Traveset, Head of ESA’s Galileo Navigation Science Office.
“These extraordinary results have been made possible thanks to the unique features of the Galileo satellites, notably the very high stabilities of their onboard atomic clocks, the accuracies attainable in their orbit determination and the presence of laser-retroreflectors, which allow for the performance of independent and very precise orbit measurements from the ground, key to disentangle clock and orbit errors.”
Figure 51: Galileo satellites 5 and 6 were delivered into faulty elongated orbits by a faulty Soyuz upper stage during their launch in 2014. This left them unable to view the entire Earth disc during the low point or perigee of their orbits, rendering their navigation payloads unusable, because they use an Earth sensor to center their signal beams. Subsequent orbital maneuvers succeeded in making their orbits more circular and their navigation payloads usable because they retained views of the entire Earth disc through each orbit. However their orbits remain elliptical compared to the rest of the Galileo constellation. Bottom view from orbital plane of nominal orbit (in blue) and injected orbit (in green) for the pair (image credit: ESA)
These parallel research activities, known as GREAT (Galileo gravitational Redshift Experiment with eccentric sATellites), were led respectively, by the SYRTE Observatoire de Paris in France and Germany’s ZARM Center of Applied Space Technology and Microgravity in Bremen, coordinated by ESA’s Galileo Navigation Science Office and supported through its Basic Activities.
Welcome results from an unhappy accident
These findings are the happy outcome of an unhappy accident: back in 2014 Galileo satellites 5 and 6 were stranded in incorrect orbits by a malfunctioning Soyuz upper stage, blocking their use for navigation. ESA flight controllers moved into action, performing a daring salvage in space to raise the low points of the satellites’ orbits and make them more circular.
Once the satellites achieved views of the whole Earth disc their antennas could be locked on their homeworld and their navigation payloads could indeed be switched on. The satellites are today in use as part of Galileo search and rescue services while their integration as part of nominal Galileo operations is currently under final assessment by ESA and the European Commission.
However, their orbits remain elliptical, with each satellite climbing and falling some 8500 km twice per day. It was these regular shifts in height, and therefore gravity levels, which made the satellites so valuable to the research teams.
Figure 52: Albert Einstein lecturing in Vienna in 1921 (image credit: Public domain)
Reenacting Einstein’s prediction
Albert Einstein predicted a century ago that time would pass more slowly close to a massive object, a finding that has since been verified experimentally several times – most significantly in 1976 when a hydrogen maser atomic clock on the Gravity Probe-A suborbital rocket was launched 10,000 km into space, confirming Einstein’s prediction to within 140 parts per million.
In fact, atomic clocks aboard navigation satellites must already take into account the fact that they run faster up in orbit than down on the ground – amounting to a few tenths of a microsecond per day, which would result in navigation errors of around 10 km daily, if uncorrected.
Figure 53: The Gravity Probe A payload of 1976, flown in a highly elliptic single orbit to measure the ‘gravitational redshift’ of Einstein’s Theory of General Relativity more accurately than ever before, seen with its designers Robert Vessot and Martin Levine of the Smithsonian Astrophysical Observatory. The experiment compared a hydrogen maser clock on Earth with its replica in space as it ascended to about 10,000 km, and confirmed theoretical expectations to an accuracy of 0.02% (https://einstein.stanford.edu)
Figure 54: Periodic modulation of the gravitational redshift for one day's orbit of the eccentrically-orbiting Galileo satellites (image credit: ESA)
The two teams relied upon the stable timekeeping of the PHM (Passive Hydrogen Maser) clocks aboard each Galileo – stable to one second in three million years – and kept from drifting by the worldwide Galileo ground segment.
“The fact that the Galileo satellites carry passive hydrogen maser clocks, was essential for the attainable accuracy of these tests,” noted Sven Hermann at the University of Bremen’s ZARM Center of Applied Space Technology and Microgravity. “While every Galileo satellite carries two rubidium and two hydrogen maser clocks, only one of them is the active transmission clock. During our period of observation, we focus then on the periods of time when the satellites were transmitting with PHM clocks and assess the quality of these precious data very carefully. Ongoing improvements in the processing and in particular in the modelling of the clocks, might lead to tightened results in the future.”
Refining the results
A key challenge over three years of work was to refine the gravitational redshift measurements by eliminating systematic effects such as clock error and orbital drift due to factors such as Earth’s equatorial bulge, the influence of Earth’s magnetic field, temperature variations and even the subtle but persistent push of sunlight itself, known as ‘solar radiation pressure’.
“Careful and conservative modelling and control of these systematic errors has been essential, with stabilities down to four picoseconds over the 13 hours orbital period of the satellites; this is four millionth of one millionth of a second,” Pacôme Delva of SYRTE Observatoire de Paris. “This required the support of many experts, with notably the expertise of ESA thanks to their knowledge of the Galileo system.”
Figure 55: Passive hydrogen maser atomic clock of the type flown on Galileo, accurate to one second in three million years (image credit: ESA)
Precise satellite tracking was enabled by the International Laser Ranging Service, shining lasers up to the Galileos’ retro-reflectors for centimeter-scale orbital checks.
Major support was also received from the Navigation Support Office based at ESA's ESOC operations center in Germany, whose experts generated the reference stable clock and orbit products for the two Galileo eccentric satellites and also determined the residual errors of the orbits after the laser measurements.
Figure 56: Satellite laser ranging station at Potsdam GFZ in Germany, part of a worldwide network known as the International Laser Ranging Service (image credit: DLR)