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Main article: "List of Galileo satellites
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Constellation visibility from a location on Earth's surface

As of 2012,[57] the system is scheduled to reach full operation in 2020 with the following specifications:

Ground segment[edit]

The system's orbit and signal accuracy is controlled by a "ground segment consisting of:

Services[edit]

The Galileo system will have five main services:

Open access navigation
This will be available without charge for use by anyone with appropriate mass-market equipment; simple timing, and positioning down to 1 metre.
Commercial navigation (encrypted)
High precision to the centimetre; guaranteed service for which service providers will charge fees.
Safety of life navigation
Open service; for applications where guaranteed precision is essential. Integrity messages will warn of errors.
Public regulated navigation (encrypted)
Continuous availability even if other services are disabled in time of crisis; Government agencies will be main users.
Search and rescue
System will pick up distress beacon locations; feasible to send feedback, e.g. confirming help is on its way.

Other secondary services will also be available.

Concept[edit]

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Space Passive Hydrogen Maser used in Galileo satellites as a master clock for an onboard timing system

Each Galileo satellite has two master passive "hydrogen maser "atomic clocks and two secondary "rubidium atomic clocks which are independent of one other.[58][59] As precise and stable space-qualified atomic clocks are critical components to any satellite-navigation system, the employed quadruple "redundancy keeps Galileo functioning when onboard atomic clocks fail in space. The onboard passive hydrogen maser clocks' precision is four times better than the onboard rubidium atomic clocks and estimated at 1 second per 3 million years (a timing error of a "nanosecond or 1 billionth of a second (10−9 or 1/1,000,000,000 s) translates into a 30 "cm (11.8 "in) positional error on Earth's surface), and will provide an accurate timing signal to allow a receiver to calculate the time that it takes the signal to reach it.[60][61][46] The Galileo satellites are configured to run one hydrogen maser clock in primary mode and a rubidium clock as hot backup. Under normal conditions, the operating hydrogen maser clock produces the reference frequency from which the navigation signal is generated. Should the hydrogen maser encounter any problem, an instantaneous switchover to the rubidium clock would be performed. In case of a failure of the primary hydrogen maser the secondary hydrogen maser could be activated by the ground segment to take over within a period of days as part of the redundant system. A clock monitoring and control unit provides the interface between the four clocks and the navigation signal generator unit (NSU). It passes the signal from the active hydrogen master clock to the NSU and also ensures that the frequencies produced by the master clock and the active spare are in phase, so that the spare can take over instantly should the master clock fail. The NSU information is used to calculate the position of the receiver by "trilaterating the difference in received signals from multiple satellites.

For more information of the concept of global satellite navigation systems, see "GNSS and "GNSS positioning calculation.

Constellation[edit]

List of Galileo satellites
Summary of satellites
Block Launch
Period
Satellite launches Currently in operational orbit
and healthy
Full success Failure Planned
"GIOVE 2005–2008 2 0 0 0
IOV 2011–2012 4 0 0 3
FOC From 2014 12 2* 16 12
Total 18 2* 16 15
* One partial launch failure resulting in 2 satellites orbiting in a degraded orbit

(Last update: 18 November 2016)
For a more complete list, see "list of Galileo satellites

Galileo satellite test beds: GIOVE[edit]

GIOVE
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"GIOVE-A was successfully launched 28 December 2005

In 2004 the Galileo System Test Bed Version 1 (GSTB-V1) project validated the on-ground algorithms for Orbit Determination and Time Synchronisation (OD&TS). This project, led by ESA and "European Satellite Navigation Industries, has provided industry with fundamental knowledge to develop the mission segment of the Galileo positioning system.[62]

A third satellite, "GIOVE-A2, was originally planned to be built by "SSTL for launch in the second half of 2008.[63] Construction of "GIOVE-A2 was terminated due to the successful launch and in-orbit operation of "GIOVE-B.

The "GIOVE Mission[64][65] segment operated by "European Satellite Navigation Industries used the "GIOVE-A/B satellites to provide experimental results based on real data to be used for risk mitigation for the IOV satellites that followed on from the testbeds. "ESA organised the global network of ground stations to collect the measurements of "GIOVE-A/B with the use of the GETR receivers for further systematic study. GETR receivers are supplied by "Septentrio as well as the first Galileo navigation receivers to be used to test the functioning of the system at further stages of its deployment. Signal analysis of "GIOVE-A/B data confirmed successful operation of all the Galileo signals with the tracking performance as expected.

In-Orbit Validation (IOV) satellites[edit]

These testbed satellites were followed by four IOV Galileo satellites that are much closer to the final Galileo satellite design. The Search & Rescue feature is also installed.[66] The first two satellites were launched on 21 October 2011 from "Guiana Space Centre using a "Soyuz launcher,[67] the other two on 12 October 2012.[68] This enables key validation tests, since earth-based receivers such as those in cars and phones need to "see" a minimum of four satellites in order to calculate their position in three dimensions.[68] Those 4 IOV Galileo satellites were constructed by Astrium GmbH and Thales Alenia Space. On 12 March 2013, a first fix was performed using those four IOV satellites.[69] Once this In-Orbit Validation (IOV) phase has been completed, the remaining satellites will be installed to reach the Full Operational Capability.

Full Operational Capability (FOC) satellites[edit]

List of Galileo satellites

On 7 January 2010, it was announced that the contract to build the first 14 FOC satellites was awarded to "OHB System and "Surrey Satellite Technology Limited (SSTL). Fourteen satellites will be built at a cost of €566M (£510M; $811M).[70] "Arianespace will launch the satellites for a cost of €397M (£358M; $569M). The European Commission also announced that the €85 million contract for system support covering industrial services required by "ESA for integration and validation of the Galileo system had been awarded to "Thales Alenia Space. Thales Alenia Space subcontract performances to "Astrium GmbH and security to "Thales Communications.

In February 2012, an additional order of eight satellites was awarded to OHB Systems for €250M ($327M), after outbidding EADS Astrium tender offer. Thus bringing the total to 22 FOC satellites.[71]

On 7 May 2014, the first two FOC satellites landed in Guyana for their joint launch planned in summer[72] Originally planned for launch during 2013, problems tooling and establishing the production line for assembly led to a delay of a year in serial production of Galileo satellites. These two satellites (Galileo satellites GSAT-201 and GSAT-202) were launched on 22 August 2014.[73] The names of these satellites are Doresa and Milena named after European children who had previously won a drawing contest.[74] On 23 August 2014, launch service provider Arianespace announced that the "flight VS09 experienced anomaly and satellites were injected into an incorrect orbit.[75]

Satellites GSAT-203 and GSAT-204 were launched successfully on 27 March 2015 from Guiana Space Centre using a Soyuz four stage launcher.[76][77] Using the same Soyuz launcher and launchpad, satellites GSAT-205 and GSAT-206 were launched successfully on 11 September 2015.[78]

Satellites GSAT-208 and GSAT-209 were successfully launched from Kourou, French Guiana, using the Soyuz launcher on December 17, 2015.[79][80][81][82]

Satellites GSAT-210 and GSAT-211 were launched on 24 May 2016 and are being commissioned.[83][84]

Starting in November 2016, deployment of the last twelve satellites will use a modified Ariane 5 launcher, named Ariane 5 ES, capable of placing four Galileo satellites into orbit per launch.[85]

Satellites GSAT-207, GSAT-212, GSAT-213, GSAT-214 were successfully launched from Kourou, French Guiana, on 17 November 2016 on an Ariane 5 ES.[86][87]

On 15 December 2016, Galileo started offering Initial Operational Capability (IOC). The services currently offered are Open Service, Public Regulated Service and Search and Rescue Service.[1]

Future evolution[edit]

As of 2014, ESA and its industry partners have begun studies on Galileo Second Generation (G2G) satellites, which will be presented to the EC for the 2020s launch period.[88] One idea is to employ "electric propulsion, which would eliminate the need for an upper stage during launch and allow satellites from a single batch to be inserted into more than one orbital plane.

Applications and impact[edit]

Science projects using Galileo[edit]

In July 2006 an international consortium of universities and research institutions embarked on a study of potential scientific applications of the Galileo constellation. This project, named GEO6,[89] is a broad study oriented to the general scientific community, aiming to define and implement new applications of Galileo.

Among the various GNSS users identified by the Galileo Joint Undertaking,[90] the GEO6,[89] project addresses the Scientific User Community (UC).

The GEO6[89] project aims at fostering possible novel applications within the scientific UC of GNSS signals, and particularly of Galileo.

The AGILE[91] project is an EU-funded project devoted to the study of the technical and commercial aspects of "location-based services (LBS). It includes technical analysis of the benefits brought by Galileo (and EGNOS) and studies the hybridisation of Galileo with other positioning technologies (network-based, WLAN, etc.). Within these project, some pilot prototypes were implemented and demonstrated.

On the basis of the potential number of users, potential revenues for Galileo Operating Company or Concessionaire (GOC), international relevance, and level of innovation, a set of Priority Applications (PA) will be selected by the consortium and developed within the time-frame of the same project.

These applications will help to increase and optimise the use of the "EGNOS services and the opportunities offered by the Galileo Signal Test-Bed (GSTB-V2) and the Galileo (IOV) phase.

Coins[edit]

The European Satellite Navigation project was selected as the main motif of a very high-value collectors' coin: the Austrian "European Satellite Navigation commemorative coin, minted on 1 March 2006. The coin has a silver ring and gold-brown "niobium "pill". In the reverse, the niobium portion depicts navigation satellites orbiting the Earth. The ring shows different modes of transport, for which satellite navigation was developed: an airplane, a car, a lorry, a train and a container ship.

Receivers[edit]

A number of devices are compatible with Galileo.[92][93]

See also[edit]

Notes[edit]

  1. ^ Orbital periods and speeds are calculated using the relations 4π²R³ = T²GM and V²R = GM, where R = radius of orbit in metres, T = orbital period in seconds, V = orbital speed in m/s, G = gravitational constant ≈ 6.673×1011 Nm²/kg², M = mass of Earth ≈ 5.98×1024 kg.
  2. ^ Approximately 8.6 times (in radius and length) when the moon is nearest (363 104 km ÷ 42 164 km) to 9.6 times when the moon is farthest (405 696 km ÷ 42 164 km).

References[edit]

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Bibliography[edit]

Further reading[edit]

  • Psiaki, M. L., "Block Acquisition of weak GPS signals in a software receiver", Proceedings of ION GPS 2001, the 14th International Technical Meeting of the Satellite Division of the Institute of Navigation, Salt Lake City, Utah, 11–14 September 2001, pp. 2838–2850.
  • Bandemer, B., Denks, H., Hornbostel, A., Konovaltsev, A., "Performance of acquisition methods for Galileo SW receivers", European Journal of Navigation, Vol.4, No. 3, pp 17–9, July 2006
  • Van Der Jagt, Culver W. Galileo : The Declaration of European Independence : a dissertation (2002). CALL #JZ1254 .V36 2002, Description xxv, 850 p. : ill. ; 30 cm. + 1 CD-ROM

External links[edit]

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