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. |
