I write at an especially exciting moment for the Galileo satellite navigation system, as two flagship European programmes combine for the very first time.
Mid-November will see the very first Galileo launch using an Ariane 5 launcher from Europe’s Spaceport in French Guiana, in place of the Soyuz that has served the constellation up until now. Four instead of two Galileo satellites will be launched at a time: The number of satellites girding the globe will rise at a single stroke from 14 to 18.
Meanwhile, the European Union is set to declare Galileo operational for initial services at the end of this year, bringing the system to the point where it can finally start serving users.
When Galileo Meets Ariane
November’s launch has been years in the making, employing a specially customized variant of Europe’s heavy-lift workhorse rocket called the Ariane 5 ES (Evolution Storable) Galileo. It has more powerful lower stages and a reignitable upper stage, first used in 2008 to supply the low-Earth orbiting International Space Station.
This new launcher design, adapted beginning in 2012 for Galileo, will carry a lower mass payload — four fully-fuelled 738-kg Galileo satellites plus their supporting dispenser — but must haul it to the much higher altitude of medium-Earth orbit, 23,522 km.
This precisely targeted orbit actually lies 300 km above the Galileo constellation’s final working altitude, leaving Ariane’s upper stage in a stable graveyard orbit, while the quartet of satellites maneuver themselves down to their final height.
Satellites. The satellites continue unchanged from those preceding them: Galileo full operational-capability (FOC) satellites with platforms from OHB in Germany and navigation payloads from Surrey Satellite Technology Ltd in the UK.
All 14 FOC satellites follow the first four in-orbit validation (IOV) satellites launched in 2011 and 2012; these four validated overall Galileo system design with the first wholly European navigation fix in March 2013.
Carrier. The four-satellite dispenser, the interface between the satellites and its launcher, is a wholly new design by Airbus Defence and Space. Its first role is to hold the satellites safely in position during their orbital flight and then to gently release them in separate directions. Its structure has been specially tuned to prevent harmful oscillations being triggered by the vibration and noise of launch. Its design was validated using complex finite-element modeling software, followed by practical testing of the dispenser together with dummy satellites.
Launcher. Ariane’s interstage Vehicle Equipment Bay, hosting the rocket’s avionic brain, underwent a redesign to reduce mass. Engineers also had to take into account this Ariane ES version’s flight time, much longer than any of its predecessors, more than four hours in all.
This involved a reworking of the launcher’s electronics and thermal subsystems, to ensure it maintains an optimal operational environment throughout a ballistic coast phase of more than three hours, between two firings of its EPS storable propellant upper stage. Two further Ariane 5 SE Galileo flights are planned to follow, one each for the remaining orbital planes.
Ground Control. This launch will mark the first time that ESA carries out launch and early operations (LEOP) for four satellites simultaneously. Usually, simply shepherding a spacecraft through the first critical days in orbit is a demanding enough task. A combined team from ESA and France’s CNES space agency based in Toulouse will make contact, establish control, and then see the four satellites through their initial critical activities. Within the combined team, each position is paired with a counterpart from the other agency to provide three mixed shifts around the clock for these first crucial days. This same team has conducted all Galileo early operations to date alternately from Toulouse or ESA’s ESOC control center in Germany.
The work starts with an initial check of on-board health and attitude, progressing to ensure each satellite’s pair of 1 x 5-meter solar wings are deployed and tracking the Sun, and then to point their antennas back towards Earth. Next comes a series of thruster firings to set the satellites onto a drift course into their final orbit, at which point they can be handed over to the Galileo Control Centre in Oberpfaffenhofen, Germany, for routine operations, and to ESA’s Redu Centre in Belgium to commence a few months of detailed payload testing.
Galileo at Your Service
Around the same time as this key launch, GSAT-210 and GSAT-211, the two previous satellites launched in May of this year, will have completed their in-orbit testing, allowing them to be formally certified as operational members of the constellation. The four new satellites should follow them into operational status by mid-2017. However, the Galileo system will reach initial operational status without these latest six satellites. The European Commission on behalf of the European Union expects to declare the system operational and ready to offer initial services before the end of this year.
This will mark a major milestone in the programme, awaited by many citizens in Europe and around the globe. Everyone with a Galileo-enabled receiver will be able to benefit from improved positioning, supplementing the already operational GPS constellation. ESA and the European GNSS Agency (GSA) have been working with European manufacturers of mass-market satnav chips and receivers to ensure that their products are Galileo-ready, offering detailed laboratory testing to close the loop between Galileo and industry.
Transition. In parallel to the declaration of initial services, there will also be an institutional change, as the GSA takes up its role overseeing the exploitation of Galileo. At the start of 2017, the formal handover of Galileo infrastructure will be initiated, targeted to conclude by the middle of the year. This mission includes not only the Galileo satellites in space but also the far-flung ground stations located on every continent, essential to the continued high-performance operations of the Galileo system. It also includes the two European Galileo control centers, with the signals overseen from Fucino in Italy and the platforms monitored from Oberpfaffenhofen, plus the communication infrastructure connecting them all together.
In the history of ESA, a research and development agency, this kind of handover to an operational body is not unprecedented; the agency handed Europe’s Meteosat weather satellites over to the newly created Eumetsat organisation, and pioneering telecommunication satellites came under the control of Eutelsat and Inmarsat. However, the Galileo ground segment will hold a special place in ESA history as one of the most complicated developments it has ever undertaken, serving to maintain the signals from the satellites to a nanosecond-scale of performance.
ESA will maintain its role of system design authority and system procurement agent, continuing to support system exploitation as it prepares for the follow-on Galileo Second Generation (G2G) design, supported through the EU’s Horizon 2020 programme. For example, the current contract of Galileo’s ground support operator will end next year, so ESA is supporting the GSA in initiating the contractual process to select a replacement operator. This contract covers all the interaction between the ground segment elements which are vital to the system as a whole. Maintaining continuity of service with transition to the new operator will certainly present a big challenge to the entire team, but one we are confident of meeting.
Upgrade. In parallel, 2017 will see the upgrade of various elements of the Galileo Ground Segment to reinforce its robustness, including updated releases to the Galileo Control Segment overseeing the satellites and the Galileo Mission Segment, overseeing the navigation signals. A new release of elements of the Galileo Security Facility, for security monitoring of the system, as well as the secure Public Regulated Service, will be deployed at the two Galileo Security Monitoring Centres.
The Galileo Ground Segment will gain a sixth tracking telemetry and control facility, for monitoring the satellite platforms in Papeete, Tahiti, and additional processing chains for increased redundancy will be deployed across the Uplink Stations in Kourou, Reunion and Noumea used to update the navigation message information. Similar redundant chains will be finalized for all 15 current Galileo Sensor Stations, which perform continuous collection of Galileo signals to identify the tiniest clock error or satellite drift.
New Satellites. The production of the satellites themselves continues to maintain a steady rhythm, with a production line stretching from suppliers across Europe to OHB and SSTL and then to ESA’s ESTEC Test Centre in the Netherlands for acceptance testing, based on a wide range of simulated space tests. The acceptance of the next satellites to launch is scheduled for this year’s end. Along with the two more Ariane 5 launches to come — one in the second half of 2017 and another in 2018 — the current plan is to commission further launch services as well as additional satellites in order to have Galileo fully operational by 2020. For these launches, Galileo may be the first customer of the new Ariane-6 launch vehicle.
EGNOS. Along with the progress of Galileo, contracts are planned to cater for the further development of the ESA-designed European Geostationary Navigation Overlay Service, Europe’s first navigation system. EGNOS was certified for safety-of-life aviation use in 2011, and is managed by the European Commission through a contract with operator the European Satellite Services Provider, based in France. ESA will support the technical evolution of EGNOS version 3, intended as multi-constellation in nature, again through the Horizon 2020 framework.
Finally, ESA is also addressing the challenges of satellite navigation beyond Galileo through the creation of the Navigation Innovation and Support Programme (NAVISP), which will be proposed to Europe’s space ministers for approval in December. Applying ESA’s expertise from Galileo and EGNOS, the optional NAVISP will undertake research work in support of ESA Member States’ national objectives and industrial competitiveness in the upstream and downstream navigation sector, including the fusion of satellite navigation with various disruptive technologies and complementary positioning techniques.