Navigation orbiter systems have its beginnings dated back to the 1970s, in which the Navy Satellite system was the first operational orbiter of its sort. This was called the ‘NAVSTAR GPS ‘ . It was used chiefly for pigboat and ship pilotages but was on occasion used in air pilotage. “ NAVSTAR uses the Doppler displacement of wireless signals transmitted from a orbiter to mensurate the comparative speed between the orbiter and the sailing master. Knowing the orbiter orbit exactly, the sailing master ‘s absolute place can be accurately determined from the clip rate of alteration of scope to the orbiter. ”[ 1 ]The NAVSTAR consisted of 10 ( 10 ) orbiters in orbit and an extra three ( 3 ) spares, but this has since been advanced. The map of executing changeless monitoring and go throughing information updates are carried out be a series of tracking Stationss. It besides consists of receiving systems and necessary power computing machines for the processing of signals. Navigation orbiter systems have its huge utilizations and applications. It is used in avionics and car trailing. This is readily seen in our twenty-four hours to twenty-four hours activities. The pilotage makes usage of personal handheld devices which GPS ( planetary placement Service ) modules imbedded in them. They receive signals from the orbiters and are accurate to ten ( 10 ) metres. Other applications include Time transportation and synchronism. Time transportation refers to the procedure of directing mention clock information to another location, whereby synchronism is the coordination of assorted events to run a system in entire understanding. Synchronism is assisted by the planetary GPS enabled timekeeping systems, therefore why it is used all around the universe. Navigation systems are besides used for ‘Location based services ‘ ( LBS ) . These involve turn uping topographic points like infirmary, clinics, eating houses and even hard currency machines by tourers in a new metropolis. These are all accessible with nomadic devices in concurrence with the nomadic web and doing usage of the ability to observe the geographical place of a device.[ 2 ]Similarly, location of employees, location based advertisement and the receiving of qui vives about traffic updates can be sent to Mobiles with the aid of location based services. Vivid illustrations of LBS can be found in ‘Google Maps ‘ , and the film: ‘Enemy of the State ‘ to advert a few. Navigation systems can besides be used in surveying, which simple put is the technique of finding the dimensions and place of points on the Earth surface. They can besides be used in hunt and deliverance operations every bit good as plus trailing. An illustration of plus trailing will be truck swift company tracking the location of one of its trucks or group of trucks. Other applications include, route pricing and in geophysical scientific disciplines. Assorted types of pilotage orbiter systems are present today. In this paper, we shall discourse a few of them ; these include the NAVSTAR-GPS, GLONASS and GALILEO which is yet to be launched.
GPS is easy said to be the bow smuggler and innovator of the Global Navigation Satellite System. In the early old ages compasses were used for pilotage. It has been a immense development in the history of world which dates back to the 1970s, where the NAVSTAR GPS became operational. This orbiter is owed and managed by the United States Department of Defence. NAVSTAR GPS was the former name, and it was developed by the Pentagon. It consists of a series of orbiters in orbit at about 19,000km revolving above the Earth. This Global Positioning system, GPS can nail a individual ‘s location anyplace on the surface of the Earth. As this system was developed and maintained by the US, section of defense mechanism, it was non made available to the populace until 1995. It was used entirely for military intents. It has been used since the Persian Gulf War to travel military personnels and steer hi-tech arms in Iraq and elsewhere in the universe.[ 3 ]
Figure 1: Satellites description of nailing a location. Retrieved from hypertext transfer protocol: //www.freeflightsystems.com/images/gpsBasics-blue.jpg
As mentioned earlier, there is a web of 20 four ( 24 ) orbiters with four ( 4 ) spares revolving the Earth at 20,200Km at least twice a twenty-four hours at approximately 11hours 58minutes each. Their orbit is in the Medium Earth Orbit ( MEO ) . They are spaced at 60 grades which are in six orbits and are inclined at 55 grades with regard to the equatorial plane. Hence with this, a user is in contact with between five to eight orbiters on any point on the surface of the Earth. This figure provides coverage over the full universe invariably. Atomic redstem storksbills which are all set exactly to the same clip and powerful wireless senders are located on the orbiter. These orbiters are recurrently conveying information about their place in infinite. The GPS units on the land which comprise of an aerial, a computing machine and a wireless receiving system are able to obtain the signals which are beamed from the orbiters. To guarantee exact location of the GPS unit, it must be locked to a lower limit of three ( 3 ) orbiters and obtain their signals, but to find the height in add-on to the longitude and latitude, it must be locked on to a lower limit of four ( 4 ) orbiters. An algorithm in the GPS unit step the clip it takes for a signal to go from the orbiter to the land in order to cipher the distance. With that information, the GPS computing machine calculates a conjectural domain around each orbiter with the radius equal to the distance from the GPS receiving system. The topographic point where four orbiter distance domains intersect is the receiving system ‘s location on the Earth. Due to the computation, the GPS can find its latitude, longitude and lift. The device passes the deliberate consequences onto local street maps, which are already loaded onto the unit. This helps to find the exact location and show it on the street maps on the device. For the GPS unit, the computing machine compares the consequences to the pre-selected finish, and determines the best path and displays it.[ 4 ]In drumhead, it operates on the footing that wireless signals which include the exact clip, passed by the atomic clock, are received by receiving systems on Earth and as such the locations are triangulated at a point for finding the exact location.
The NAVSTAR GPS system, which is a national military system is widely used today both commercially and internationally. The system consists of chiefly three sections, the Space section, Control section and the User section. The infinite section consists of all the orbiters revolving the Earth. The diagram below is an illustration of the infinite section. Satellites use atomic redstem storksbills to keep synchronised signals which are transmitted over the same frequence of 1575.45 MHz ; the minimal strength signal received on Earth is about -158dBw to -160dBw.[ 5 ]Since early 2008, the GPS configuration has been increased to 31 orbiters with the two older 1s working as spares. [ update ] With the extra orbiters being put up in topographic point, the GPS receiving system computations have been increased, therefore bettering the preciseness. This helps to convey about redundancy and dependability of the system. With this, the original configuration was changed to a no-uniform agreement and the sums of orbiters that can be seen from the land at any point in clip have been at approximately eight ( 8 ) .[ 6 ]
Figure 2: Configuration of a NAVSTAR GPS system. Retrieved from hypertext transfer protocol: //media.obsessable.com/media/2009/01/21/24satellite-gps.jpg
The Control section consists of all the land Stationss involved in supervising the full system which are located all around the universe. These include the Master Control Station, an Alternate Master Control Station, the Ground aerials and the Monitor Stationss. The maestro control station is located on Falcon air force base, Colorado, USA. Each of the proctor Stationss has the functionality of measuring. They perform measurings of the signals from the orbiters which are included as a portion into the orbital theoretical account of each orbiter. These orbital theoretical accounts calculate the orbital informations and orbiter clock rectification for each orbiter. The maestro control station so uploads this derived orbital and clock informations to the orbiter which in bend sends the information to the GPS receiving systems through wireless signals. The user section as mentioned earlier consists of the GPS users, both military and commercial. These GPS receiving systems convert the signals in infinite to speed, clip and place estimations. This is why it is said that four orbiters are needed to happen the X, Y, Z and clip co-ordinates. Many receiving systems can be used at the same time, because they are inactive. Many of the applications of GPS have been mentioned earlier. These include location based services, tracking, pilotage etc.
The GPS orbiter transmits two microwave bearer signals viz. L1 and L2 at 1575.42 MHz and 1227.70 MHz severally. The Course codification ( C/A codification ) which is available for private usage is broadcast at L1 and this is called Standard placement service ( SPS ) . The Precise Code ( P-Code ) is for military or authorised use merely. This is broadcast at both L1 and L2 ; hence the truth of this is better. Consequently the section of defense mechanism, by utilizing Selective handiness, have unnaturally degraded the truth of the standard placement service. This is done as a consequence of the service being available to everyone, hence it will deny hostile forces the tactical advantage of GPS positioning. The clock and orbital informations are falsified by the upholder of the system, therefore selective handiness is the most of import factor for all beginnings of mistake.[ 7 ]
GLONASS is the Russian opposite number of the US NAVSTAR GPS. It stands for Globaluaya Navigatsionnaya Sputnikovaya Sistema, ( Global Navigation Satellite System ) . GLONASS was developed by the former Soviet Union, and is now managed for the Russian Federation Government by the Russian Space Forces. The system is operated by the Coordination Scientific Information Centre ( KNITs ) of the Ministry of Defence of the Russian Federation. The development of this system began in 1976 and they aimed at doing it be available for planetary coverage by 1991. In 1983, the first orbiters were launched. This was a trial sequence and the configuration had four to six orbiters. Between 1986 and 1993, there were 12s ( 12 ) orbital orbiters and the flight trial had been completed. By1995, the configuration of 20 four ( 24 ) orbiters was completes and full operation began. The GLONASS system consists of the Orbital Constellation of GLONASS Satellites, The Ground Control Segment, the Rocket-Space Complex and the Users. The diagram below is a dislocation of the sections. The Ground Control section provides GLONASS with all the necessary orbiter control. In this section, there is the system control station, telemetry, tracking and control Stationss which are all distributed all over the Russian Federation. The assorted maps performed by the Ground Control Segment include the supervising the normal operation of the orbital configuration, uninterrupted accommodation of orbiters orbital parametric quantities, and the coevals of control bids and particular information to be uploaded. In order for optimum operation to be in the pilotage system, synchronism of all procedure during system operation must be achieved. As a consequence of this demand, the synchronism system contains a Central synchroscope – “ a stationary ultra-stable H frequence criterion, which is used as the footing for GLONASS clip graduated table coevals ” .[ 8 ]All the on board clip graduated tables are synchronized with the system clip graduated table and the cardinal synchroscope is synchronized with the province clip and frequence. The deployment and care of the orbital configuration is provided by two infinite systems based on two launchers viz. “ Proton ” and “ Soyuz ” . Each infinite system includes launcher, supporter and satellite systems.
Figure 3: GLONASS System Architecture. Retrieved from Russian Aerospace Agency, Schepkina 42, Moscow 129090, Russia, from “ The Global Navigation Satellite System GlONASS: Development and Usage in the twenty-first Century hypertext transfer protocol: //tycho.usno.navy.mil/ptti/ptti2002/paper13.pdf
Similar to the GPS, it was developed entirely for military intents, but is now used for commercial intents. It has really many of its features similar to the NAVSTAR GPS system. It has twenty one ( 21 ) orbiters in orbit with an extra three ( 3 ) spares. Unlike the NAVSTAR GPS which has six ( 6 ) orbital planes, it has three ( 3 ) . These planes are separated at angles of 120 grades and the orbiters within the same orbit stage at 45 grades. Its planes are inclined at 64.8 grades with regard to the equatorial plane. The configuration of orbiters is in the orbit of 19,100Km and revolve the Earth about 11hours 15minutes a twenty-four hours. With this configuration agreement, at least five ( 5 ) orbiters are seeable from the Earth at any one point in clip. Again, it transmits signals in the L-band. It besides offers two degrees of service, which are the Channel of Standard Accuracy ( CSA ) and the Channel of High Accuracy ( CHA ) . The former is available for civil usage and provides really good truth, while the ulterior that provides even better truth is merely available for authorized usage. As earlier mentioned, each orbiter transmits two codifications, C/A and P-Code on two frequences. The expression can be used to find the frequence that they transmit at. The L1 set is determined by 1602MHz + thousand * ( 9/16 ) MHz and the L2 set is calculate by 1246MHz + thousand * ( 7/16 ) MHz. K is given by the frequence channel of the orbiter n consideration.[ 9 ]The major difference between the GPS and GLONASS is the type of geographic mention systems in which the co-ordinates are delivered. The GPS outputs informations in the World Geodetic System 1987 ( WGS84 ) format, while the GLONASS end products in the PZ-90 System which is the Russian parametric quantity of Earth 1990. Second, there is the clip system difference. GPS uses the Universal Coordinated Time and the USNO ( US Naval Observatory ) clip while the GLONASS uses the UTC in Moscow clip. Yet another important difference as can be seen in this paper is in the signal construction and handling of these two systems. The GPS use the same frequences but are different in the single codifications, while the GLONASS use the same codification but differ in frequences.[ 10 ]
GALILEO is the European Union ( EU ) and European Space Agency ( ESA ) opposite number to the NAVSTAR GPS and the GLONASS. The European Union decided that they needed to present their ain orbiter called Galileo for assorted grounds. Some of these grounds include, deriving liberty and no longer depending on the USA for pilotages and orbiter services. GALILEO is presently being put into service and visualised through a series of civilian standards and non military as the US opposite number is. Hence it will be a strictly civilian pilotage system. This system is perceived to besides hold a higher preciseness pilotage system. This betterment over its predecessors will be achieved through the usage of Binary off-Set Code Modulation ( BOC ) and multiplexed Binary Off-Set Code Modulation ( MBOC ) . GALILEO promises to offer a new ‘Alarm ‘ characteristic in the current hunt and deliverance maps provided by some organisations and besides ensures to supply increased security through the usage of unity messages. These will immediately inform users of mistakes that develop and besides warrant handiness. Consequently, GALILEO will supply world-wide coverage and offer better response that GPS. This will be possible because of its orbital configuration. Although there are many other grounds why GALILEO is being developed by the EU, it is deserving to observe that GALIELO will supply more services. These services include: Open Service ( OS ) , Commercial Service ( CS ) , Safety of Life service ( SOL ) , Public regulated Service ( PRS ) , Search and Rescue ( SAR ) .
For the Open service, the transmittal frequences are the same with the GALILEO system and the GPS L1 frequence, as a consequence, there will be more signals of clip and place making the receiving system on Earth and this will supply improved response. This service is given for free and is intended for mass market applications. In this service, GALILEO does non accept any liability and does non give any warrant of handiness. As the name implies, Commercial Service will be a fee based service and it is imagined to be for market applications which require higher public presentation as compared to the Open Service. Such applications could include high velocity informations transmittal and exact clip related services. The Safety of Life services is chiefly for conveyance applications. This service will be deployed utilizing the air power communicating channels L1 and E5. The primary difference between this and the Open Service is the high degree of unity information that is provided to services like rail traffic, air power etc. If a pilotage system fails it can take to a life endangering state of affairs, therefore why two channels will be used to direct the SoL service. The Public Regulated Service is one which will be controlled by a civilian bureau, but will supply a changeless, uninterruptable and unafraid service for governmental intents including military intents. The bulk of the users here will include the Police, Border Patrol, fire sections and other jurisprudence enforcement organic structures who protect the safety of persons. This service is confirmed to be protected against intervention and misrepresentation caused by electronic devices, this is necessary because this service may be required during times of crisis.[ 11 ]Finally, the Search and deliverance service is to be used by human-centered hunt and deliverance squads. The usage of exigency senders and orbiter will assist in the location of trades and individuals. The GALILEO hunt and deliverance service is planned to better the bing service ( COSPAS-SARSAT ) which has six ( 6 ) Low Earth Orbit ( LEO ) and five ( 5 ) geostationary ( GEO ) orbiters by supplying instantaneous exigency calls from any topographic point on the Earth and finding the exact location of beacons with more truth. Besides with more orbiters in the medium Earth orbit ( MEO ) being portion of the configuration of GALILEO, it will supplement the bing LEO and GEO orbiters of the COSPAS-SARSAT system and overcome hinderances during suboptimal conditions.[ 12 ]
Figure 4: Configuration of Galileo orbiters
ESA: European Space Agency, ( 2010 ) , Galileo Navigation, retrieved from hypertext transfer protocol: //www.esa.int/esaNA/SEMJQSXEM4E_galileo_0.html on 7th March, 2010.
We have discussed the motive behind the development of the GALILEO system, its assorted services and now we shall discourse the engineering and the construction behind GALILEO. GALILEO ‘s configuration consists of 30 ( 30 ) orbiters of which three ( 3 ) of them are spares. They will be placed at orbits of 23,222Km above the Earth ‘s surface and revolve the Earth at periods of 14 hours 5 proceedingss. These orbiters are inclined at an angle of 56 grade with regard to the equatorial plane.[ 13 ]Each of the Galileo orbiters are expected to hold a lifetime of 15 ( 15 ) old ages and their needed power of 1500W will be generated by big solar panels. Each of these orbiters will direct wireless signals to the land section at intervals of 100 proceedingss. At any given clip, there are ever two control centres that will be in connexion to the orbiter and a telemetry and tele-command station that will supervise the wellness of the orbiters. ” There are besides 30 ( 30 ) detector Stationss for finding, satellite clock synchronism, and unity monitoring. ”[ 14 ]
Figure 5: Galileo Architecture. Retrieved from Wilfried Bornemann ( 2004 ) , Acta Astronica, Navigation Satellite Systems Galileo, issue 54, pp 821-823
The land station like any other land station consists of a series of control Centres. They perform assorted undertakings such as supervising signal unity and coordination or deliverance service to advert a few. As earlier mentioned, there are different services that will be available with GALILEO. As a consequence of this, there are different frequences, transition formats and informations transmittal rates that will be used. The primary transition formats are BPSK and BOC. An understanding has been signed with the US and EU on the GPS and GALILEO systems to guarantee interoperability between the two systems so as to guarantee its purposes and aims are attained. The end of the GALILEO undertaking has been defined and experimental orbiters have been deployed. They are in good operation and they are proving the difficult conditions in infinite and the atomic redstem storksbills. Currently it is expected that the GALILEO system will to the full operational by the twelvemonth 2014.
In this paper, we have discussed fundamentally three types of pilotage systems, but there is a Chinese opposite number who has four ( 4 ) geostationary orbiters in orbit and they transmit over China. The system is known as the Beidou system. The full system is yet to be launched and made operations in 2013, but this is non ascertained yet. This is known as the Beidou 2 or Compass system ( Compass Navigation Satellite System ) . It will hold five GEO orbiters and 30 ( 30 ) MEO satellites in its configuration.[ 15 ]It is planned to offer two services, unfastened and authorized services.
In decision, the three systems, viz. , GALILEO, GPS and GLONASS work together to jointly do up what is called Global Navigation Satellite System ( GNSS ) . Together they will offer truth, unity and handiness. In this paper all the differences of the 3s systems including their similarities have been pointed out. The start of the development of GPS and GLONASS were in 1973 and 1972 severally while GALILEO ‘s development began in 2001. GPS foremost orbiter was launched on 22 February, 1978, GLONASS on 12 October 1982 and GALILEO on 28 December 2005. The figure of orbiter in their several configurations are 24 orbiters with 4 spares for GPS, the GLONASS is planned to hold 24 operational orbiters with 3 spare and the GALILEO is planned to hold 27 orbiters with 3 spares every bit good. The GPS has 6 orbital ‘s with an disposition of 55 grades to the equator and an height of 20, 180KM. GLONASS has 3 orbital ‘s with an disposition of 64.8 grade and an height of 19,100Km while the GALILEO has 3 Orbital ‘s at an disposition of 56 grades to the equator and is at an height of 23,222Km. Each of them has different orbital periods of 11 hours 58 proceedingss, 11 hours 16minutes and 14 hours 5 proceedingss severally. They all vary in the clip system they use, which are GPS-Time, GLONASS-Time and GST ( Galileo system clip ) . GPS and GALILEO both operate on CDMA while GLONASS operates on FDMA. As it is known, GPS and GLONASS have services shared for both military and civilian, and is controlled by the US section of Defence and the Russian Defence ministry severally, while GALILEO has assorted service totaling up to 5 chiefly for civilians and is controlled by the civilian authorities of the EU. Can it therefore be deduced which system is best? In my sentiment a combination of the systems to work in concurrence will be an optimal system.