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Advanced Aviation Technology Ltd.
 
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Galileo - European Satellite Navigation System

Kim O'Neil
Advanced Aviation Technology Ltd.
September 2001

Abstract

Europe is moving closer to the launch of its satellite navigation system Galileo. This will lead to a fully civilian controlled global satellite navigation system, with much improved navigation services and a certified positioning service. It will be fully compliant with ICAO's requirements for satellite navigation systems. The overall benefits include redundancy and integrity to meet the safety requirements of civil aviation and help the full introduction of satellite navigation for all phases of flight.

Whilst the battle with GPS is likely to be bitter, in the end these two systems will benefit each other and massively extend the role of satellite navigation.

1. Introduction

Galileo is an initiative of the European Union, in collaboration with the European Space Agency and European Industry, to launch a European financed global satellite navigation system under civilian control. The satellite navigation market in Europe is rapidly expanding - growing from just under a Billion Euro in 1999 to over 8 Billion Euro by 2005 alone. Accordingly, following ratification by the European Transport ministers, ESA will begin launching Galileo satellites in 2004 with a full constellation ready to begin operational service in 2007. Current work aims to develop the architecture and design required to provide high precision navigation, position, timing and integrity information to meet both user needs and public obligations, such as safety for all transport modes.

Galileo is proposed as a Public Private Partnership formed between the European Union, ESA and a consortium of private companies. The PPP partners include Astrium, Alcatel Space, Alenia Spazio and Thales. Galileo is, naturally enough, still a subject of intense negotiation and debate between the EU and its commercial partners, with the EU Council of Ministers pressing for a single and efficient management structure.

Galileo is also a part of the EU's wider strategic plan for space exploitation, which includes its programme for Global Monitoring, Environment and Security (GMES) - where 'security' also embraces safety - and is part of a joint strategy developed with ESA.

Although largely a European programme, Galileo will also involve much international cooperation e.g. with the Russian Federation (on frequency sharing and validation). The total cost of Galileo is expected to be around 3 Billion Euros - shared equally between the private consortium partners and the EU.

The calculated benefits and the direct and indirect revenues from Galileo are expected to be substantial, fully justifying Europe's commitment. Galileo is very much a commercial initiative aimed at capturing a significant share of the satellite navigation market. It is not a flag waving exercise. The commercial, technical and market benefits have been carefully studied and laid out in very detailed market studies. As a result, civil aviation will be a major beneficiary of Galileo, although aviation is still only a very small percentage (around 1%) of the satellite navigation market.

In July 1999, the European Union set out the definition phase of Galileo. This included a cost benefit analysis to address the:

  • Potential sources of revenue;
  • Public Private Partnership arrangements;
  • Feasibility, design, capability, structure, reliability, control and costs;
  • Development, validation, deployment and operation of Galileo
  • Detailed analysis of costs and finance;
  • Integration of user and service provider needs;
  • Optimise integration of EGNOS;
  • Integrity requirements and other requirements at high latitudes;
  • Additional research and development tasks;
  • Frequency allocations via WRC;
  • Security issues;
  • Cooperation possibilities with other countries.

The objectives of this work were to prepare the case for a final decision to launch Galileo.

2. The General Benefits of Galileo

Galileo is a system that will benefit all modes of transport including road, rail, sea and air travel. Galileo will, in particular, result in real and direct benefits to civil aviation. The clearest of these is the fact that satellite navigation will become a fully redundant service for civil aviation users in the event of a satellite or system failure. The number of satellites in view will grow dramatically and become fully independent in the case of failure to either GPS or Galileo. Galileo will work with GPS to provide greatly improved satellite coverage and availability, ensuring that sufficient satellites are always in view to obtain an optimal navigation solution. This has been one of the major impediments of a GPS only system and one stumbling block to the potential wider benefits that satellite navigation could offer civil aviation, but which it has not so far been able to deliver.

Certified services will also be offered, with guaranteed service levels (in terms of accuracy, redundancy, integrity, reliability and availability) and a more robust signal in space. This will enable the global implementation of ICAO's CNS/ATM concept.

These benefits will bring satellite navigation forward as a realistic replacement for conventional navigation aids in civil aviation. Despite the fact that satellite navigation has been with us for some time and that airlines have made significant investments, there has been, so far, relatively little return in terms of improved navigation services to airlines. Galileo looks set to change this and accelerate the introduction and benefits of satellite navigation for civil aviation Users.

Galileo also complies with the need for civil aviation services to be free and unfettered, a fundamental requirement enshrined in the ICAO convention.

The Users

Four basic services have been defined from User studies:

  • Position, Velocity and Time service (PVT)
    A basic service aimed at mass-market applications, free of charge.
  • Accuracy and Integrity service (AI)
    High accuracy and availability for less demanding safety of life users and professional markets - a subscriber service.
  • Ranging and Timing service (RT)
    Very precise ranging, positioning and timing signals for the professional and technical markets - a subscriber service.
  • High Integrity service (HI)
    Provides the highest integrity, availability, continuity and resistance to signal interference for safety of life markets. Restricted to trusted subscribers.

The relationship between Risk and Integrity is mapped in diagram X

(Insert Risk/Integrity Diagram here)

3. Galileo Programme Schedule

The definition phase of Galileo is already complete. The current phase is concerned with the detailed design and development of the full Galileo system. The schedule for Galileo will gather pace with a Galileo Test-Bed to be launched (in 2003) as piggyback payload on a next generation GLONASS satellite. Following this, the 'In-Orbit Validation' phase will begin, deploying a small constellation of satellites in 2004. An initial operational capability, consisting of twelve satellites, is planned for 2006. The full system will be finally deployed by the end of 2007 and become fully operational in 2008.

There is a definite "window of opportunity" for Galileo and it is believed that any delay in launching Galileo will lead to significant damage to Europe's entry into the mass navigation market. Hence there are strong incentives for the launch of Galileo to be brought forward.

4. The Design of Galileo

Galileo will consist of a constellation of 30 satellites in Medium Earth Orbit (MEO) only. The 30 Galileo satellites will be 3 orbital planes inclined at 54° and at an altitude of around 23,000 km. This is the simplest system to launch, operate and maintain and one that provides the greatest reliability for an operational service. Galileo satellites will weigh around 650 kg when in orbit and will generate approximately 1,500 watts of electrical power. The satellite geometry has been designed for the launch of multiple satellites with an Ariane launcher. Smaller launchers are envisaged for the replacement of individual satellites. A lot of sophisticated technology will go into Galileo, including highly advanced atomic clocks - giving greater accuracy and stability and being light weight with low power requirements. Sophisticated (next generation) electronics and the latest high performance antennas will be incorporated into the satellite, to generate the signal-in-space.

5. Galileo Ground Control System

The proposed architecture of the Galileo system includes:

  • Navigation System Control Centre,
  • A network of stations monitoring Galileo satellite orbits and synchronisation
  • Several tracking, telemetry and command ground stations

The integrity monitoring ground stations may also be co-located with the main ground control system and with the remote ground control and satellite monitoring stations.

The Galileo Navigation System Control Centre will collect the raw data from the ground stations that are monitoring the orbits of individual satellites and calculate the ephemeris data and timing offset for each satellite. This will then be up-linked to the satellite and broadcast as part of the data message for the Galileo signal-in-space.

Galileo System Time, is maintained by a Precision Timing Station, which consists of a number of high performance atomic clocks.

6. Galileo Integrity

Galileo will offer the required level of integrity required for the provision of service guarantees and for safety-of-life applications. Integrity will be provided by broadcasted alerts to the users (via Galileo satellites themselves). These will indicate when Galileo signals are outside their specification (e.g. in case of satellite clock drift). The receiver can then reject signals from these satellites or use RAIM (Receiver Autonomous Integrity Monitoring), to reduce the effect on the calculated position.

As noted above, integrity will be monitored by a network of ground stations. Integrity data will be up-linked to the Galileo satellites and then broadcast to users, superimposed on the navigation signal. A time-to-alert of six seconds has been set as a design requirement, this will ensure that civil aviation requirements are fully met. Galileo is also designed to guarantee that users will always receive integrity data through at least two satellites, each with a minimum elevation of 25°.

7. Spectrum Issues

One of the major concerns over GPS is the lack of spectrum protection. In order to ensure that a particular part of the spectrum can be used for safety of life applications - especially for global operations - adequate arrangements must be put in place to protect the spectrum. These arrangements must be sufficient for the application. This entails gaining agreement not only on the use of a particular part of the spectrum, but ensuring that services and users in adjacent parts of the spectrum do not radiate interfering signals into the radio navigation band and degrade the navigation service. GPS does not have this protection, as it was planned as a US military application and is not afforded the protection provided to the civil Aeronautical Radio Navigation (ARNS) band - protection that has been negotiated over many years.

Hence, protecting frequencies is vital for the safety of a radio navigation service. Satellite navigation also requires several frequencies (to cope with interference and compensate for atmospheric and other effects. Spectrum needs to be found and steps taken to protect each of these frequencies. This is not so easy to do, due to the intense competition for frequencies (which have a very high commercial value) and the sometimes incompatible nature of the applications that share the radio spectrum.

In fact, both GPS and Galileo will be competing for spectrum not only with each other, but also with other civil aviation services such as DME, Radar and MLS. In addition, Satellite navigation not only requires frequencies for broadcasting navigation signals but also to uplink and downlink communications to and from the satellite constellation itself. To add to this, both narrowband and broadband navigation services are envisaged. Frequencies for narrow band services are easier to obtain, but more difficult to protect. Conversely, spectrum for broadband services are difficult to obtain but easier to protect. The resulting demands on the spectrum can sometimes appear bewildering.

Currently, it looks as if these spectrum issues can be resolved and that additional services for both GPS and Galileo can be provided without adverse affects on each. Even the most pessimistic studies indicate that both systems will be compatible with each other. This greatly enhances the value and benefits of satellite navigation - especially to civil aviation Users.

8. The Politics of Galileo

The major issues surrounding Galileo are to do with its management and control. The Public Private Partnership (PPP) also raises issues about the objectives of an essentially commercial project that involves significant public money. Both the public and private partners want assurances from the other side. Until these assurances are given, the full funding will not be released. Yet few in Europe really doubt the 'knock on' commercial benefits of Galileo. A final decision on Galileo may be deferred until the end of 2001. GPS is, of course, funded entirely from military budgets.

In the meantime, around £100M ECU will be made available by the EU, to be followed by a further 450M ECU following the final decision of the EU Transport Council. ESA has also released funds. A Memorandum of Understanding (MOU) has been signed between the EC and the 10 European PPP companies (who include Astrium, Alcatel space, Alenia Spazio and Thales) and this should lead to the formal decision of the EU Transport Council and the formation of a PPP vehicle company for the Galileo programme in due course.

Naturally enough, there is opposition to Galileo. Unsurprisingly, the loudest opposing voices are from those who want GPS to be the sole satellite navigation system (although not everyone in the US thinks this way). The US may continue to make carefully timed announcements about GPS in an attempt to stall or derail Galileo, but these are unlikely to have any real effect. Most participants understand that the exploitation of satellite navigation is still in its infancy. There are so many products (many yet undreamed of) that can incorporate satellite navigation that there is simply no question about the fact that this market is BIG! As an example, navigation receivers will shortly be introduced into mobile phones.

One of the most sensitive issues, is the fact that Galileo will be a purely civil navigation service and will not be controlled by the military. Although this aspect is often played down by the US, it has certainly delayed the exploitation of GPS in civil aviation. Conversely, there is much muttering about the military applications of satellite navigation (guided weapons etc.) and the need to inhibit satellite navigation in time of war. Consequently, there will be a great deal of public (and not so public) debate about both Galileo and GPS for many years hence.

9. Summary

The implementation of Galileo will be a welcome improvement to navigation services. Galileo will vastly improve the accuracy, redundancy, integrity, reliability and availability of satellite navigation. It will provide certified services and a level of integrity not achievable with GPS. More than anything else, it will enable the full exploitation of satellite navigation for the benefit of civil aviation and hasten the implementation of ICAO's CNS/ATM concept. This will lead to genuine improvements for all phases of flight and a significant safety benefits.

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Advanced Aviation Technology Ltd.
The Old Post Office,
The Street, Compton,
Surrey GU3 1ED. ENGLAND.
Tel. +44 1483 811 311.

Email: kim.oneil@aatl.net

 
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