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1. Gps technıque term project

   Group 6 Zeren Şenyıldız-010090609 Özge Kazan- Azize Uyar-010090610 Zehra Koç- Mohsen Feizabadi- 010100910 Mustafa Serkan Işık- Atabak Sadeghinaibin- 010080918

2. Topıc: FeaturesandClassificationsof ArtificialSatellitesforGPS andGNSS:Signal, Lifespan, Orbits, anddetails.

3. What Is a Satellıte? A satellite is a moon, planet or machine that orbits a planet or star. For example, Earth is a satellite because it orbits the sun. Likewise, the moon is a satellite because it orbits Earth. Usually, the word "satellite" refers to a machine that is launched into space and moves around Earth or another body in space. Earth and the moon are examples of natural satellites. Thousands of artificial, or man-made, satellites orbit Earth. Some takenpictures of the planet that help meteorologists predict weather and track hurricanes. Some takenpictures of other planets, the sun, black holes, dark matter or faraway galaxies. These pictures help scientists better understand the solar system and universe.
4. Still other satellites are used mainly for communications, such as beaming TV signals and phone calls around the world. A group of more than 20 satellites make up the Global Positioning System, or GPS. If you have a GPS receiver, these satellites can help figure out your exact location. Satellites vary in size. Some cube satellites are as small as 10 cm. Some communication satellites are about 7 m long and have solar panels that extend another 50 m. The largest artificial satellite is the International Space Station (ISS).(This is a habitable space laboratory. At an altitude of 400 km, the ISS travels at a speed of 28 000 km/h and orbits the Earth once every 92 minutes. Scientists inside the ISS are able to perform many valuable experiments in a microgravity environment.) The main part of this is as big as a large five-bedroom house, but including solar panels, it is as large as a rugby field.
5. Artıfıcal satellıtes An artificial satellite is an object that people have made and launched into orbit using rockets. There are currently over a thousand active satellites orbiting the Earth. The size, altitude and design of a satellite depend on its purpose. Types of Satellite: Navigation satellites: The GPS (global positioning system) is made up of 24 satellites that orbit at an altitude of 20 000 km above the surface of the Earth. The difference in time for signals received from four satellites is used to calculate the exact location of a GPS receiver on Earth. Communication satellites: These are used for television, phone or internet transmissions, for example, the Optus D1 satellite is in a geostationary orbit above the equator and has a coverage footprint to provide signals to all of Australia and New Zealand.
6. Weather satellites: These are used to image clouds and measure temperature and rainfall. Both geostationary and low Earth orbits are used depending on the type of weather satellite. Weather satellites are used to help with more accurate weather forecasting. Earth observation satellites: These are used to photograph and image the Earth. Low Earth orbits are mainly used so that a more detailed image can be produced. Astronomical satellites: These are used to monitor and image space. A satellite such as the Hubble Space Telescope orbits at an altitude of 600 km and provides very sharp images of stars and distant galaxies. Other space telescopes include Spitzer and Chandra.
7. The first artificial satellite was the Soviet Sputnik 1 mission, launched in 1957. Since then, dozens of countries have launched satellites, with more than 3,000 currently operating spacecraft going around the Earth. There are estimated to be more than 8,000 pieces of space junk; dead satellites or pieces of debris going around the Earth as well.
8. WHAT IS GPS ? The Global Positioning System (GPS) is a U.S.owned utility that provides users with positioning, navigation, and timing services. This system consists of three segments: the space segment, the control segment, and the user segment. The U.S. Air Force develops, maintains, and operates the space and control segments. Space Segment: The GPS space segment consists of a constellation of satellites transmitting radio signals to users. The Air Force manages the constellation to ensure the availability of at least 24 GPS satellites, 95% of the time. For the past several years, the Air Force has been flying 31 operational GPS satellites, plus 3-4 decommissioned satellites ("residuals") that can be reactivated if needed.
9. Control Segment: The GPS control segment consists of a global network of ground facilities that track the GPS satellites, monitor their transmissions, perform analyses, and send commands and data to the constellation. The current operational control segment includes a master control station, an alternate master control station, 12 command and control antennas, and 16 monitoring sites.
10. Gps Applications : Agriculture,Environment, Marine, Public safety & Disaster relief, Rail, Recreation, Roads & Highways, Space, Surveying & Mapping, Timing..
11. GLONASS GLObalnayaNAvigatsionnayaSputnikovayaSistema
12. GLONASS GLONASSis a space-basedsatellitenavigationsystemoperatedbythe Russian AerospaceDefenceForces. It is designed to provide instantaneous, high precision location and speed information to users throughout most of the world. Deployed in nearly circular orbits at an altitude of 19,100 km by Proton boosters. GLONASS positional accuracies (95% confidence) are claimed to be 100 m on the surface of the Earth, 150 m in altitude, and 15 cm/s in velocity. GLONASS is a dual-use system. A fullyoperationalconstellationwith global coverageconsists of 24 satellites, while 18 satellitesarenecessaryforcoveringtheterritory of Russia. Toget a positionfixthereceivermust be in therange of at leastfoursatellites.
13. Deployment of the GLONASS constellation Beginningon 12 October 1982, numerousrocketlaunchesaddedsatellitestothesystemuntiltheconstellationwascompleted in 1995. When completed, the GLONASS constellation was designed to provide 100 meters accuracy with its "standard precision" C/A signals, which are deliberately degraded, and 10-20 meter accuracy with its P "high-precision" signals, originally available exclusively to the military. Thisbroughttheprecision of GLONASS on-par withtheAmericanGPSsystem, whichhad achievedfulloperationalcapability а yearearlier. Afterthefullcomplementwasachieved in December1995, therewerenofurtherlaunchesuntilDecember1999, becauseof financiallydifficultperiod.
14. GLONASS deployment milestones: 18 satellites in constellation – 2007 24 satellites in constellation – 2009
15. At the end of 2004, the head of the Federal Space Agency, FKA, called the separation between military and civilian frequencies in the GLONASS system, "awkward" and promised to provide the access to the high-precision navigation data to all users. GLONASS signal is free (available in latitude, longitude and altitude).Overthethreedecades of development, thesatellitedesignshavegonethroughnumerousimprovements, and can be dividedintothreegenerations: - Theoriginal GLONASS (since 1982), - GLONASS-M (since 2003) and- GLONASS-K (since 2011). 
16. GLONASS (Uragan) The GLONASS (also called Uragan) satellite features a three-axis stabilization system, which points it in nadir during the operational flight. Two solar arrays provide power supply. Onboard cesium clocks provide time accuracy to 1,000 nanoseconds. Thefirstgeneration GLONASS satelliteswere 7.8 m tall, had a width of 7.2 m, measuredacrosstheir solar panels, and a mass of 1,260 kg. (Scale model of the Uragansatellite.)
17. GLONASS-M Glonass-M weredevelopedbeginning in 1990 andfirstlaunched in 2003, launches of GLONASS-M satellites were expected to continue until 2012. The GLONASS-M version of the satellite featured improved antennas, extended lifetime and the introduction of a separate transmission frequency dedicated to civilian users, known as L2. The satellite also sported an increased clock stability, more accurate solar array orientation and better maneuverability. It had a slightlylargermassthanthebaseline GLONASS, standing at 1,415 kg, but it had doubletheoriginal'slifetime, decreasingtherequiredreplacement rate by50%. Thenewsatellitealso had betteraccuracyandabilitytobroadcasttwoextraciviliansignals.
18. GLONASS-K Thefirst GLONASS-K satellitewassuccessfullylaunched on 26 February 2011. The GLONASS-K version featured lighter, standardized unpressurized bus. It has an operationallifetime of 10 years, comparedtothe 7-year lifetime of thesecondgeneration GLONASS-M.Itwilltransmitmorenavigationsignalstoimprovethesystem'saccuracy.GLONASS-K2A revised version of GLONASS-K satellite, known as GLONASS-K2 was originally promised as early as 2013, however by 2012, it was not expected to enter service until 2015. Group launch by SOYUZ
19. GLONASS MODERNİZATİON
20. Interaction with American GPS Russia discussed various issues related to the development and use of GLONASS in parallel with American GPS and European Galileo systems. According to the head of Federal Space Agency, in December 2004 Russia and the US discussed the ways of preventing the use of satellite navigation systems by terrorists.
21. GPS = GLONASS ? The fundamental difference between the GLONASS and GPS navigators are the signal itself and its structure. - GPS system uses code-division channeling. GLONASS uses frequency-division channeling. - The structure of the signal also differs.- Also the satellites motion is described using fundamentally different mathematical models. In GLONASS differential model of motion is used. And GPS uses a model based on osculating elements. - GLONASS time and GPS time are not the same. (Leap seconds are an issue) - GLONASS uses a different geocentric datum.(PZ-90)
22. Participation in Europe's Galileo network Russia also was in talks with the European Space Agency on the possible cooperation on the Galileo navigation network. Details beyond the possibility of launching Galileo satellites onboard Soyuz rockets were not specified. Cooperation with ChinaNumber of contacts between Russian and Chinese space officials included discussions of the GLONASS network. According to the Russian media, China considered the development of its own satellite navigation system, which could involve purchases of the Russian technology.
23. GLONASS Ground Control Thegroundcontrolsegment of GLONASS is almostentirelylocatedwithinformerSovietUnionterritory, exceptfor a station in Brasilia, Brazil.TheGround Control Center and Time Standards is locatedinMoscowandthetelemetryandtrackingstationsare in Saint Petersburg,Ternopol, Eniseisk, andKomsomolsk-na-Amure.
24. GALILEO The Galileo programmeis Europe's initiative for a state-of-the-art global satellite navigation system, providing a highly accurate, guaranteed global positioning service under civilian control. The system is intended primarily for civilian use, unlike the more military-oriented systems of the United States (GPS), Russia (GLONASS), and China (Beidou-1/2, COMPASS).The fully deployed system will consist of 30 satellites and the associated ground infrastructure. Galileo will be inter-operable with GPS and GLONASS, the two other global satellite navigation systems.
25. The first two operational Galileo satellites were launched from Europe's Spaceport in French Guiana in October 2011. Once the In-Orbit Validation (IOV) phase has been completed, the remaining satellites will be placed in orbit at regular intervals to reach Full Operational Capability.
26. The complete Galileo constellation will comprise satellites spread evenly around three orbital planes inclined at an angle of 56 degrees to the equator. Each satellite will take about 14 hours to orbit the Earth. One satellite in each plane will be a spare, on stand-by should any operational satellite fail.
27. The Galileo IOV satellite Mass                                                        about 700 kgSize with solar wings stowed              3.02 x 1.58 x 1.59mSize with solar wings deployed             2.74 x 14.5 x 1.59 mDesign life                                                more than 12yearsAvailable power                                      1420 W (sunlight) / 1355 W (eclipse) Orbit Altitude                                                         23 222 kmInclination                                                     56°
28. Three initial services will be provided from 2014 onwards: The Open Service: Galileo open and free of user charge signal, The Public Regulated Service: a special Galileo navigation service using encrypted signals set up for better management of critical transport and emergency services, better law enforcement, improved border control and safer peace missions, The Search And Rescue Service, contribution of Europe to COSPAS-SARSAT, an international satellite-based search and rescue distress alert detection system. Another services will be tested as of 2014 and provided as the system reaches full operational capability with the 30 satellites: The Commercial Service that gives access to two additional encrypted signals.
29. Research is under way into future improvements such as expanded augmentation coverage, including how best to support increased navigation in the Arctic region as ice cover recedes, even more precise atomic clocks, and inter-satellite links to reduce Galileo’s dependence on its ground segment for clock correction.
30. COMPASS The BNSS (BeiDou Navigation Satellite System) is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, and a full-scale global navigation system that is currently under construction. The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1,  consists of three satellites and offers limited coverage and applications. It has been offering navigation services, mainly for customers in China and neighboring regions, since 2000. The second generation of the system, officially called the BeiDou Satellite Navigation System (BDS) and also known as COMPASS or BeiDou-2, will be a global satellite navigation system and is under construction as of January 2013. Consisting of 35 satellites, it became operational in China in December 2011, with 10 satellites in use, and began offering services to customers in the Asia-Pacific region in December 2012. For future, it is planned to begin serving global customers upon its completion in 2020.
31. Description BeiDou-2 (formerly known as COMPASS) is not an extension to the older BeiDou-1, but rather supersedes it outright. The new system will be a constellation of:  35 satellites  which include 5 geostationary orbit satellites for backward compatibility with BeiDou-1  30 non-geostationary satellites (27 in medium earth orbit and 3 in inclined geosynchronous orbit), that will offer complete coverage of the globe.
32. Accuracy There are two levels of service provided:  a free service to civilians : has a 10-meter location-tracking accuracy, synchronizes clocks with an accuracy of 10 nanoseconds, and measures speeds to within 0.2 m/s.  licensed service to the Chinese government and military: has a location accuracy of 10 centimetrescan be used for communication, and will supply information about the system status to the user. To date, the military service has been granted only to the People's Liberation Army and to the Military of Pakistan
33. Aims The ranging signals are based on the CDMA principle and have complex structure typical of Galileo or modernized GPS.  Similar to the other GNSS, there will be two levels of positioning service: open and restricted (military). The public service shall be available globally to general users.  When all the currently planned GNSS systems are deployed, the users will benefit from the use of a total constellation of 75+ satellites, which will significantly improve all the aspects of positioning, especially availability of the signals in so-called urban canyons.  The general designer of Compass navigation system is Sun Jiadong, who is also the general designer of its predecessor, the original Beidou navigation system.
34. List of satellites (as of December 2012)[edit] Date Launcher Satellite Orbit Usable System 10/31/2000 LM-3A BeiDou-1A GEO 59°E No BeiDou-1 12/21/2000 LM-3A BeiDou-1B GEO 80°E No 5/25/2003 LM-3A BeiDou-1C GEO 110.5°E No 2/3/2007 LM-3A BeiDou-1D SupersyncorbitNo 4/14/2007 LM-3A Compass-M1 MEO ~21,500 km Testing only BeiDou-2 (Compass) 4/15/2009 LM-3C Compass-G2 ? No 1/17/2010 LM-3C Compass-G1 GEO 144.5°E Yes 6/2/2010 LM-3C Compass-G3[55] GEO 84°E Yes 8/1/2010 LM-3A Compass-IGSO1 118°E incl 55° Yes 11/1/2010 LM-3C Compass-G4 GEO 160°E Yes 12/18/2010 LM-3A Compass-IGSO2 118°E incl 55° Yes 04/10/2011 LM-3A Compass-IGSO3 118°E incl 55° Yes 07/26/2011 LM-3A Compass-IGSO4 95°E incl 55° Yes 12/02/2011 LM-3A Compass-IGSO5 95°E incl 55° Yes 02/24/2012 LM-3C Compass-G559°E Yes 04/29/2012 LM-3B Compass-M3 MEO incl 55° Yes 04/29/2012 LM-3B Compass-M4 MEO incl 55° Yes 09/18/2012 LM-3B Compass-M5 MEO incl 55° Yes 09/18/2012 LM-3B Compass-M6 MEO incl 55° Yes 10/25/2012 LM-3C Compass-G6[48] 80°E Yes
35. Compass-M1 – Detailed Information Compass-M1 is an experimental satellite launched for signal testing and validation and for the frequency filing on 14 April 2007. The role of Compass-M1 for Compass is similar to the role of the GIOVE satellites for the Galileo system. The orbit of Compass-M1 is nearly circular, has an altitude of 21,150 km and an inclination of 55.5 degrees. Compass-M1 transmits in 3 bands: E2, E5B, and E6. In each frequency band two coherent sub-signals have been detected with a phase shift of 90 degrees (in quadrature). These signal components are further referred to as "I" and "Q". The "I" components have shorter codes and are likely to be intended for the open service. The "Q" components have much longer codes, are more interference resistive, and are probably intended for the restricted service. The investigation of the transmitted signals started immediately after the launch of Compass -M1 on 14 April 2007. Soon after in June 2007, engineers at CNES reported the spectrum and structure of the signals. A month later, researchers from Stanford University reported the complete decoding of the “I” signals components. The knowledge of the codes allowed a group of engineers at Septentrio to build the COMPASS receiver and report tracking and multipath characteristics of the “I” signals on E2 and E5B. Characteristics of the "I" signals on E2 and E5B are generally similar to the civilian codes of GPS (L1-CA and L2C), but Compass signals have somewhat greater power. The notation of Compass signals used in this page follows the naming of the frequency bands and agrees with the notation used in the American literature on the subject, but the notation used by the Chinese seems to be different and is quoted in the first row of the table.
36. For Future According to the authorities." The system became operational in the China region that same month. The global navigation system should be finished by 2020.As of December 2012, 16 satellites for BeiDou-2 have been launched, 14 of them are in service.
37. Classification of Artificial and GPS satellite orbits 1.Centric classifications Galactocentric orbit is an orbit about the center of a galaxy. The Sun follows this type of orbit about the galactic center of the Milky Way. Heliocentric orbit is an orbit around the Sun. In our Solar System, all planets, comets, and asteroids are in such orbits. Geocentric orbit is an orbit around the planet Earth, such as that of the Moon or of artificial satellites. Areocentric orbit is an orbit around the planet Mars, such as that of its moons or artificial satellites. Lunar orbit is an orbit around the Earth’s moon.
38. 2. Altitude classifications for geocentric orbits Low Earth orbit (LEO): Geocentric orbits with altitudes up to 2,000. Medium Earth orbit (MEO): Geocentric orbits ranging in altitude from 2,000 km to just below geosynchronous, matching the Earth's sidereal rotation period orbit at 35,786 kilometres. Also known as an intermediate circular orbit. These are most commonly at 20,200 kilometres or 20,650 kilometres with an orbital period of 12 hours and are used by the Global Positioning System. Other satellites in Medium Earth Orbit include GLONASS (with an altitude of 19,100 kilometres) and GALILEO (with an altitude of 23,222 kilometres) constellations. Geosynchronous orbit is an orbit around the Earth with an orbital period of one sidereal day (23 hours 56 minutes and 4 seconds)
39. 2. Altitude classifications for geocentric orbits Medium Earth orbit (MEO) High Earth orbit: Geocentric orbits above the altitude of geosynchronous orbit 35,786.
40. 3. Inclination classifications Inclined orbit is an orbit whose inclination in reference to the equatorial plane is not 0. Polar orbit: An orbit that passes above or nearly above both poles of the planet on each revolution. Therefore it has an inclination of (or very close to) 90 degrees. Polar Sun-synchronous orbit: A nearly polar orbit that passes the equator at the same local solar time on every pass.
41. 3. Inclination classifications Non-inclined orbit: An orbit whose inclination is equal to zero with respect to some plane of reference. Ecliptic orbit is a non-inclined orbit with respect to the ecliptic. Equatorial orbit is a non-inclined orbit with respect to the equator. Near equatorial orbit: An orbit whose inclination with respect to the equatorial plane is nearly zero.
42. 4. Eccentricity classifications There are two types of orbits: Closed (periodic) orbits: Circular and elliptical orbits Open (escape) orbits: Parabolic and hyperbolic orbits. Circular orbit: An orbit that has an eccentricity of 0 and whose path traces a circle. Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an ellipse. The orbits of GPS are nearly circular, with a typical eccentricity of lessthan 1.
43. 5. Synchronicity classifications Geostationary orbit (GEO): A circular geosynchronous orbit with an inclination of zero. To an observer on the ground this satellite appears as a fixed point in the sky. All geostationary orbits must be geosynchronous, but not all geosynchronous orbits are geostationary. It is 35,786 kilometres above the Earth's equator and following the direction of the Earth's rotation. An object in such an orbit has an orbital period equal to the Earth's rotational period (one sidereal day), and thus appears motionless, at a fixed position in the sky, to ground observers. Communications and weather satellites are often given geostationary orbits.
44. GPS SIGNALS Each satellite transmits a regular GPS signal that is carried by radio waves in the microwave part of the electromagnetic spectrum GPS satellite transmits data on two frequencies, L1 (1575.42 Mhz) and L2 (1227.60 MHz) L5 is the third civilian GPS signal, designed to meet demanding requirements for safety-of-life transportation and other high-performance applications.
45. What does the signal consist of? Digital Informations: Two pseudorandom noise (PRN) codes, along with satellite ephemerides (Broadcast Ephemerides), ionospheric modeling coefficients, status information, system time, and satellite clock corrections First pseudorandom noise (PRN) code is the Course-Acquisition (C/A) code. Second pseudorandom noise code is the Precise Code, or P code
46. Coarse-Acquisition (C/A) code The C/A code is the base for all civil GPS receivers modulated onto the L1 carrier Selective Availability(SA) -intentional degradation of public GPS signals implemented for national security reasons.
47. Effect of selectıve avaılabılıty The data indicates a circular error of only 2.8 meters and a spherical error of 4.6 meters during the first few hours of SA-free operation COURTESY OF GPS Support Center, Air Force Space Command
48. Effect of selectıve avaılabılıty NOAA National Geodetic Survey
49. Precise Code The P- and Y-code are the base for the precise (military) position determination The P code is ten times as fast, which means it can determine the pseudorange ten times more accurately Carriedby both L1 and L2 codes Since January 31, 1994 the AS-system is operating continuously and the P-code is only transmitted as Y-code AS-anti spoofing-encryption of P codes into Y codes
50. Navigation message low frequency signal added to the L1 codes that gives information about the satellite's orbits, their clock corrections and other system status(BasicallyAlmanacdata andEphemerisdata) Ephemeris data is data that tells the GPS receiver where each GPS satellite should be at any time throughout the day Complexitymaysometimes be an advantage/ GPS receivers know the PRN codes for each satellite and so can not only decode the signal but distinguish between different satellites
51. GPS signal error Ionosphere and troposphere delays Multipat Receiver clock errors Orbital errors Satellite geometry/shading
52. Satellite geometry/shading When the satellites are all in the same part of the sky, readings will be less accurate.
53. GPS Modernization It is the policy of the United States to maintain U.S. leadership in the service, provision, and use of satellite navigation systems. The U.S. government has additional policy goals to meet growing demands by improving the performance of GPS services, and to remain competitive with international satellite navigation systems. The GPS modernization program is an ongoing, multibillion-dollar effort to upgrade the GPS space and control segments with new features to improve GPS performance. These features include new civilian and military signals. New Civil Signals Future Satellite Generations Control Segment Modernization Program Schedule
54. New Civil Signals (L2C,L5,L1C) A major focus of the GPS modernization program is the addition of new navigation signals to the satellite constellation. The government is in the process of fielding three new signals designed for civilian use: L2C, L5, and L1C. The legacy civil signal, called L1 C/A or C/A at L1, will continue broadcasting in the future, for a total of four civil GPS signals. The new civil signals are phasing in incrementally as the Air Force launches new GPS satellites to replace older ones. Most of the new signals will be of limited use until they are broadcast from 18 to 24 satellites. Second Civil Signal (L2C): designed specifically to meet commercial needs. Third Civil Signal(L5): designed to meet demanding requirements for safety-of-life transportation and other high-performance applications. Fourth Civil Signal (L1C): designed to enable interoperability between GPS and international satellite navigation systems.
55. Current and Future Satellite Generations The GPS constellation is a mix of new and legacy satellites. GPS Block IIA: It is an upgraded version of the GPS Block II satellites launched in 1989-1990. The "II" refers to the second generation of GPS satellites, although Block II was actually the first series of operational GPS satellites. The "A" stands for advanced. GPS Block IIR: The IIR series were produced to replace the II/IIA series as the II/IIA satellites. The "R" in Block IIR stands for replenishment. GPS Block IIR(M): The IIR(M) series of satellites are an upgraded version of the IIR series. The "M" in IIR(M) stands for modernized, referring to the new civil and military GPS signals added with this generation of spacecraft. GPS Block IIF: The IIF series expand on the capabilities of the IIR(M) series with the addition of a third civil signal. The "F" in IIF stands for follow-on. Compared to previous generations, GPS IIF satellites have a longer life expectancy and a higher accuracy requirement.
56. Current and Future Satellite Generations GPS Block III: the GPS III series is the newest block of GPS satellites.It will provide more powerful signals in addition to enhanced signal reliability, accuracy, and integrity. As of April 2013, GPS III Satellite Vehicles (SVs) 03-08 are in the Production and Deployment Phase. Future versions will feature increased capabilities to meet demands of military and civilian users alike. Control Segment Modernization As part of the GPS modernization program, the Air Force has continuously upgraded the GPS control segment over the past few years and will keep doing so in the years to come. It includs the Architecture Evolution Plan (AEP) and the Next Generation Operational Control System (OCX).
57. The schedule for the parallel space and control segment upgrades

58. References:

    http://en.wikipedia.org/wiki/satellite http://www.sciencelearn.org.nz/Contexts/Satellites/Science-Ideas-and-Concepts/Artificial-satellites http://www.nasa.gov/audience/forstudents/5-8/features/what-is-a-satellite-58.html#.UqoABPRdXw- http://www.gps.gov/ http://www.csr.utexas.eduUnıversıty of texas Croucher, Phil.Professional Helicopter Pilot Studies. 2007 http://www.oxts.com/glossary/coarse-acquisition/ http://ec.europa.eu/enterprise/policies/satnav/galileo/ http://www.gsa.europa.eu/galileo/programme http://en.wikipedia.org/wiki/galileo_%28satellite_navigation http://www.esa.int/our_activities/navigation/the_future_-_galileo/galileo_satellites