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Galileo Ground Segment: Difference between revisions
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==Ground Control Segment== | ==Ground Control Segment== | ||
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The Ground Control Segment (GCS) is responsible for satellite constellation control and management of Galileo satellites. It provides the telemetry, telecommand and control function for the whole Galileo satellite constellation. Its functional elements are deployed within the Galileo Control Centers (GCC) and the five globally distributed Telemetry Tracking and Control (TT&C) stations. To manage this, the GCS will use a global network of nominally five TTC stations to communicate with each satellite on a scheme combining regular, scheduled contacts, long-term test campaigns and contingency contacts. | The Ground Control Segment (GCS) is responsible for satellite constellation control and management of Galileo satellites. It provides the telemetry, telecommand and control function for the whole Galileo satellite constellation. Its functional elements are deployed within the Galileo Control Centers (GCC) and the five globally distributed Telemetry Tracking and Control (TT&C) stations. To manage this, the GCS will use a global network of nominally five TTC stations to communicate with each satellite on a scheme combining regular, scheduled contacts, long-term test campaigns and contingency contacts. | ||
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==Ground Mission Segment== | ==Ground Mission Segment== | ||
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The Galileo Mission Segment (GMS) will use a global network of nominally thirty Galileo Sensor Stations (GSS) to monitor the navigation signals of all satellites on a continuous basis, through a comprehensive communications network using commercial satellites as well as cable connections in which each link will be duplicated for redundancy. The prime element of the GSS is the Reference Receiver. | The Galileo Mission Segment (GMS) will use a global network of nominally thirty Galileo Sensor Stations (GSS) to monitor the navigation signals of all satellites on a continuous basis, through a comprehensive communications network using commercial satellites as well as cable connections in which each link will be duplicated for redundancy. The prime element of the GSS is the Reference Receiver. | ||
Revision as of 13:58, 11 April 2011
| GALILEO | |
|---|---|
| Title | Galileo Ground Segment |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
The GALILEO Space Segment will be complemented by the GALILEO Ground Segment, which will comprise a pair of control centres and a global network of transmitting and receiving stations.
The core of the GALILEO ground segment will be the two control centres (GCC). Each control centre will manage 'control' functions supported by a dedicated Ground Control Segment (GCS) and 'mission' functions, supported by a dedicated Ground Mission Segment (GMS). The GCS will handle spacecraft housekeeping and constellation maintenance while the GMS will handle navigation system control.[1]
Ground Control Segment
The Ground Control Segment (GCS) is responsible for satellite constellation control and management of Galileo satellites. It provides the telemetry, telecommand and control function for the whole Galileo satellite constellation. Its functional elements are deployed within the Galileo Control Centers (GCC) and the five globally distributed Telemetry Tracking and Control (TT&C) stations. To manage this, the GCS will use a global network of nominally five TTC stations to communicate with each satellite on a scheme combining regular, scheduled contacts, long-term test campaigns and contingency contacts.
The TTC Stations will be large, with 13-metre antennas operating in the 2 GHz Space Operations frequency bands. During normal operations, spread-spectrum modulation, similar to that used for Tracking and Data Relay Satellite System (TDRSS) and ARTEMIS data relay applications, will be used, to provide robust, interference free operation. However, when the navigation system of a satellite is not in operation (during launch and early orbit operations or during a contingency) use of the common standard TTC modulation will allow non-ESA TTC stations to be used.
Ground Mission Segment
The Galileo Mission Segment (GMS) will use a global network of nominally thirty Galileo Sensor Stations (GSS) to monitor the navigation signals of all satellites on a continuous basis, through a comprehensive communications network using commercial satellites as well as cable connections in which each link will be duplicated for redundancy. The prime element of the GSS is the Reference Receiver.
The GMS communicates with the Galileo satellites through a global network of Mission Up-Link Stations (ULS), installed at five sites, each of which will host a number of 3-metre antennas. ULSs will operate in the 5 GHz Radionavigation Satellite (Earth-to-space) band.
The GMS will use the GSS network in two independent ways. The first is the Orbitography Determination and Time Synchronisation (OD&TS) function, which will provide batch processing every ten minutes of all the observations of all satellites over an extended period and calculates the precise orbit and clock offset of each satellite, including a forecast of predicted variations (SISA - Signal-in-Space Accuracy) valid for the next hours. The results of these computations for each satellite will be up-loaded into that satellite nominally every 100 minutes using a scheduled contact via a Mission Up-link Station.
The second use of the GSS network is for the Integrity Processing function (IPF), which will provide instantaneous observation by all GSSs of each satellite to verify the integrity of its signal. The results of these computations, for the complete constellation, will be up-loaded into selected satellites and broadcast such that any user will always be able to receive at least two Integrity Messages.
The Integrity messages will comprise two elements. The first is as an “Integrity Flag”, which warns that a satellite signal appears to exceed its tolerance threshold. This flag will be generated, disseminated and broadcast with the utmost urgency, so that the Time-to-Alert, being the period between a fault condition appearing at a user's receiver input and the Integrity Flag appearing there will be no more than six seconds, and will be re-broadcast a number of times. The second element of the Integrity Message comprises Integrity Tables, which will be broadcast regularly to ensure that new users or users who have missed recent signal (for example when travelling through a tunnel) will be able to reconstitute the system status correctly.
The OD&TS operation thus monitors the long-term parameters due to gravitational, thermal, ageing and other degradations, while the IPF monitors short-term effects, due to sudden failure or change.
Launching and phases
ESA will launch the first four operational satellites using two separate launchers. The first two satellites will be placed in the first orbital plane and the second in the second orbital plane. These four satellites, plus part of the ground segment, will then be used to validate the Galileo system as a whole, together with advanced system simulators. Then, the next two satellites will be launched into the third orbital plane. They will be followed by several launches with Ariane-5 or Soyuz from the Europe’s Space Port in French Guyana. The first services will be delivered when the constellation has reached its Initial Orbital Configuration. When the 30 satellites are in space on all its three orbital planes, Galileo will be fully operational, providing its services to a wide variety of users throughout the world.
The assembly of the first four satellites in the future constellation, which will be launched in 2011-2012 as ESA has confirmed, is currently being completed. The creation of the terrestrial element of the infrastructure is continuing in parallel; this involves choosing sites and building a large number of stations spread across a number of countries and regions of the world: Belgium, France, Italy, Germany, Spain, the Netherlands, the United Kingdom, New Caledonia, Réunion, French Guyana, Tahiti, Sweden, Norway, the United States, Antarctica (Troll, Adélie Land), etc.
Work on the deployment phase was launched in 2008 and is proceeding actively. This work has been divided up essentially into six packages, each of which is the subject of a public procurement procedure. Competitive dialogue with the tendering firms is a key element in the procedures which have been launched. As a result, the first four contracts, with a total value of around € 1 250 million, were awarded in 2010; they are for the packages covering system engineering support, satellite construction (with an initial order for 14 satellites), launchers (for the launch of 10 satellites, but with options for additional launches) and operations, respectively. The other two packages, relating to ground infrastructure, will be awarded in 2011. The contracts for additional equipment and facilities will also need to be awarded in the course of 2011.
The public procurement contracts already awarded are enabling the Commission to adjust its approach to meet the deadline of 2014. Accordingly, the development and deployment phases will continue in parallel until 2012, when the development phase will be completed, and the exploitation phase for the first services will start in 2014. A first stage will be the partial commissioning of the infrastructure (initial operational capability, or IOC) as from 2014-2015 and the provision of the open service, the search and rescue service and the PRS. At this stage, however, accuracy and availability will not yet have reached their optimum levels.
The European GNSS has one prime advantage over other systems: it is the only one designed for civilian purposes and under civilian control. It has other potential advantages which should not be disregarded, such as its commercial service, which might make it possible to authenticate signals and further improve the accuracy of the open service. Finally, its open service complements, and is interoperable with, the American GPS, so that the combined use of the two systems will afford a degree of reliability and accuracy which is likely to fulfil most users' needs worldwide in the mass applications market. However, most of these benefits will materialise only after the full infrastructure is complete. Galileo's Full Operational Capability (FOC) should be achieved in 2019-2020. It might change, depending on availability of financing, technical problems and industrial performance.[2]