The Galilean Alternative

The base Open Service is to be available without charge to anyone with a Galileo-compatible receiver , with an encrypted higher-bandwidth improved-precision Commercial Service available at a cost. Initially GPS reserved the highest quality signal for military use, and the signal available for civilian use was intentionally degraded Selective Availability.

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This changed with President Bill Clinton signing a policy directive in to turn off Selective Availability. Since May the same precision signal has been provided to both civilians and the military. Since Galileo was designed to provide the highest possible precision greater than GPS to anyone, the US was concerned that an enemy could use Galileo signals in military strikes against the US and its allies some weapons like missiles use GNSSs for guidance.

The frequency initially chosen for Galileo would have made it impossible for the US to block the Galileo signals without also interfering with its own GPS signals. Some US officials became especially concerned when Chinese interest in Galileo was reported.

An anonymous EU official claimed that the US officials implied that they might consider shooting down Galileo satellites in the event of a major conflict in which Galileo was used in attacks against American forces. At first, EU officials did not want to change their original plans for Galileo, but have since reached the compromise that Galileo is to use a different frequency.

This allowed the blocking or jamming of either GNSS without affecting the other.

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One of the reasons given for developing Galileo as an independent system was that position information from GPS can be made significantly inaccurate by the deliberate application of universal Selective Availability SA by the US military. GPS is widely used worldwide for civilian applications; Galileo's proponents argued that civil infrastructure, including airplane navigation and landing, should not rely solely upon a system with this vulnerability.

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On 2 May , SA was disabled by the President of the United States, Bill Clinton ; in late the entity managing the GPS confirmed that they did not intend to enable selective availability ever again. The European Union also agreed to address the "mutual concerns related to the protection of allied and US national security capabilities. On 30 November the 27 EU transport ministers involved reached an agreement that Galileo should be operational by , [27] but later press releases suggest it was delayed to In early the EU had yet to decide how to pay for the system and the project was said to be "in deep crisis" due to lack of more public funds.

European Union research and development projects could be scrapped to overcome a funding shortfall. In November , it was agreed to reallocate funds from the EU's agriculture and administration budgets [32] and to soften the tendering process in order to invite more EU companies. In June , the European Court of Auditors published a report, pointing out governance issues, substantial delays and budget overruns that led to project stalling in , leading to further delays and failures. In October , the European Commission cut the number of satellites definitively planned from 28 to 22, with plans to order the remaining six at a later time.

The launch of the first four in-orbit validation IOV satellites was planned for the second half of , and the launch of full operational capability FOC satellites was planned to start in late The first four pairs of satellites were launched on 22 August , 27 March , 11 September and 17 December In January , news agencies reported that six of the passive hydrogen maser and three of the rubidium atomic clocks had failed.

Four of the full operational satellites have each lost at least one clock; but no satellite has lost more than two. The operation of the constellation has not been affected as each satellite is launched with three spare clocks. The possibility of a systemic flaw is being considered. Additionally some refurbishment is required for the rubidium atomic clocks that still have to be launched.

For the passive hydrogen masers operational measures are being studied to reduce the risk of failure. In September , China joined the Galileo project. On 3 June the EU and Ukraine signed an agreement for Ukraine to join the project, as noted in a press release. As of November , Morocco also joined the programme. In November , China opted instead to upgrade BeiDou navigation system , its then-regional satellite navigation system.

On 30 November , the 27 member states of the European Union unanimously agreed to move forward with the project, with plans for bases in Germany and Italy. Spain did not approve during the initial vote, but approved it later that day.

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This greatly improved the viability of the Galileo project: As a member of ESA , it already collaborated in the development of the Galileo satellites, contributing the state-of-the-art hydrogen-maser clocks. Switzerland's financial commitment for the period — will be calculated in accordance with the standard formula applied for the Swiss participation in the EU research Framework Programme.

As of , [72] the system is scheduled to reach full operation in with the following specifications:.

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The system's orbit and signal accuracy is controlled by a ground segment consisting of:. The system transmits three signals: Each Galileo satellite has two master passive hydrogen maser atomic clocks and two secondary rubidium atomic clocks which are independent of one other. 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.

The onboard passive hydrogen maser and rubidium clocks are very stable over a few hours. If they were left to run indefinitely, though, their timekeeping would drift, so they need to be synchronized regularly with a network of even more stable ground-based reference clocks. These include active hydrogen maser clocks and clocks based on the caesium frequency standard, which show a far better medium and long-term stability than rubidium or passive hydrogen maser clocks. These clocks on the ground are gathered together within the parallel functioning Precise Timing Facilities in the Fucino and Oberpfaffhofen Galileo Control Centres.

The ground based clocks also generate a worldwide time reference called Galileo System Time GST , the standard for the Galileo system and are routinely compared to the local realizations of UTC, the UTC k of the European frequency and time laboratories. Satellites will be equipped with a transponder which will relay distress signals from emergency beacons to the Rescue coordination centre , which will then initiate a rescue operation. At the same time, the system is projected to provide a signal, the Return Link Message RLM , to the emergency beacon, informing them that their situation has been detected and help is on the way.

This latter feature is new and is considered a major upgrade compared to the existing Cospas-Sarsat system , which does not provide feedback to the user.

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. 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. These testbed satellites were followed by four IOV Galileo satellites that are much closer to the final Galileo satellite design. On 12 March , a first fix was performed using those four IOV satellites.

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Thus bringing the total to 22 FOC satellites. On 7 May , the first two FOC satellites landed in Guyana for their joint launch planned in summer [91] Originally planned for launch during , problems tooling and establishing the production line for assembly led to a delay of a year in serial production of Galileo satellites. Starting in November , 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.

As of , ESA and its industry partners have begun studies on Galileo Second Generation satellites, which will be presented to the EC for the late s launch period. In July an international consortium of universities and research institutions embarked on a study of potential scientific applications of the Galileo constellation. This project, named GEO6, [] is a broad study oriented to the general scientific community, aiming to define and implement new applications of Galileo.

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.

The European Satellite Navigation project was selected as the main motif of a very high-value collectors' coin: 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: A number of devices are compatible with Galileo.

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Until late , GNSS was not authorized for use in the United States, and as such, only variably worked on devices that could receive Galileo signals, within United States territory. From Wikipedia, the free encyclopedia. Geodesy Geodynamics Geomatics History. List of Galileo satellites. Retrieved 15 December Retrieved 28 April Retrieved 12 January Retrieved 13 October Retrieved 21 June Retrieved 23 September Retrieved 30 December Retrieved on 29 October Information References 19 Citations Files Plots.

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