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ular position satellite orbital position errors are caused by radio wave refraction gravity field changes as the earth s gravitational field is not uniform and other phenomena a team led by harold l jury of pan am aerospace division in florida from 1970 1973 found solutions and or corrections for many error sources citation needed using real time data and recursive estimation the systematic and residual errors were narrowed down to accuracy sufficient for navigation 9 principles edit further information gps principles and gps navigation equations part of an orbiting satellite s broadcast includes its precise orbital data originally the us naval observatory usno continuously observed the precise orbits of these satellites as a satellite s orbit deviated the usno sent the updated information to the satellite subsequent broadcasts from an updated satellite would contain its most recent ephemeris modern systems are more direct the satellite broadcasts a signal that contains orbital data from which the position of the satellite can be calculated and the precise time the signal was transmitted orbital data include a rough almanac for all satellites to aid in finding them and a precise ephemeris for this satellite the orbital ephemeris is transmitted in a data message that is superimposed on a code that serves as a timing reference the satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation the receiver compares the time of broadcast encoded in the transmission of three at sea level or four which allows an altitude calculation also different satellites measuring the time of flight to each satellite several such measurements can be made at the same time to different satellites allowing a continual fix to be generated in real time using an adapted version of trilateration see gnss positioning calculation for details each distance measurement regardless of the system being used places the receiver on a spherical shell at the measured distance from the broadcaster by taking several such measurements and then looking for a point where they meet a fix is generated however in the case of fast moving receivers the position of the signal moves as signals are received from several satellites in addition the radio signals slow slightly as they pass through the ionosphere and this slowing varies with the receiver s angle to the satellite because that changes the distance through the ionosphere the basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centred on four satellites satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators and then using techniques such as kalman filtering to combine the noisy partial and constantly changing data into a single estimate for position time and velocity einstein s theory of general relativity is applied to gps time correction the net result is that time on a gps satellite clock advances faster than a clock on the ground by about 38 microseconds per day 10 applications edit gnss satellites used for navigation on a smartphone in 2021 main article gnss applications further information automotive navigation system the original motivation for satellite navigation was for military applications satellite navigation allows precision in the delivery of weapons to targets greatly increasing their lethality whilst reducing inadvertent casualties from mis directed weapons see guided bomb satellite navigation also allows forces to be directed and to locate themselves more easily reducing the fog of war now a global navigation satellite system such as galileo is used to determine users location and the location of other people or objects at any given moment the range of application of satellite navigation in the future is enormous including both the public and private sectors across numerous market segments such as science transport agriculture etc 11 the ability to supply satellite navigation signals is also the ability to deny their availability the operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires global navigation satellite systems edit in order of first launch year orbit size comparison of gps glonass galileo beidou 2 and iridium constellations the international space station the hubble space telescope and geostationary orbit and its graveyard orbit with the van allen radiation belts and the earth to scale a the moon s orbit is around 9 times as large as geostationary orbit b in the svg file hover over an orbit or its label to highlight it click to load its article launched gnss satellites 1978 to 2014 gps edit main article global positioning system first launch year 1978 the united states global positioning system gps consists of up to 32 medium earth orbit satellites in six different orbital planes the exact number of satellites varies as older satellites are retired and replaced operational since 1978 and globally available since 1994 gps is the world s most utilized satellite navigation system glonass edit main article glonass first launch year 1982 the formerly soviet and now russian glo bal naya na vigatsionnaya s putnikovaya s istema global navigation satellite system or glonass is a space based satellite navigation system that provides a civilian radionavigation satellite service and is also used by the russian aerospace defence forces glonass has full global coverage since 1995 and with 24 active satellites beidou edit main article beidou navigation satellite system first launch year 2000 beidou started as the now decommissioned beidou 1 an asia pacific local network on the geostationary orbits the second generation of the system beidou 2 became operational in china in december 2011 12 the beidou 3 system is proposed to consist of 30 meo satellites and five geostationary satellites igso a 16 satellite regional version covering asia and pacific area was completed by december 2012 global service was completed by december 2018 13 on 23 june 2020 the bds 3 constellation deployment is fully completed after the last satellite was successfully launched at the xichang satellite launch center 14 galileo edit main article galileo satellite navigation first launch year 2011 the european union and european space agency agreed in march 2002 to introduce their own alternative to gps called the galileo positioning system galileo became operational on 15 december 2016 global early operational capability eoc 15 at an estimated cost of 10 billion 16 17 the system of 30 meo satellites was originally scheduled to be operational in 2010 the original year to become operational was 2014 18 the first experimental satellite was launched on 28 december 2005 19 galileo is expected to be compatible with the modernized gps system the receivers will be able to combine the signals from both galileo and gps satellites to greatly increase the accuracy the full galileo constellation consists of 24 active satellites 20 the last of which was launched in december 2021 21 2 the main modulation used in galileo open service signal is the composite binary offset carrier cboc modulation regional navigation satellite systems edit navic edit main article navic the navic or navigation with indian constellation is an autonomous regional satellite navigation system developed by indian space research organisation isro the government approved the project in may 2006 and consists of a constellation of 7 navigational satellites 22 3 of the satellites are placed in the geostationary orbit geo and the remaining 4 in the geosynchronous orbit gso to have a larger signal footprint and lower number of satellites to map the region it is intended to provide an all weather absolute position accuracy of better than 7 6 metres 25 ft throughout india and within a region extending approximately 1 500 km 930 mi around it 23 an extended service area lies between the primary service area and a rectangle area enclosed by the 30th parallel south to the 50th parallel north and the 30th meridian east to the 130th meridian east 1 500 6 000 km beyond borders 24 a goal of complete indian control has been stated with the space segment ground segment and user receivers all being built in india 25 the constellation was in orbit as of 2018 and the system was available for public use in early 2018 26 navic provides two levels of service the standard positioning service which will be open for civilian use and a restricted service an encrypted one for authorized users including military there are plans to expand navic system by increasing constellation size from 7 to 11 27 qzss edit main article quasi zenith satellite system the quasi zenith satellite system qzss is a four satellite regional time transfer system and enhancement for gps covering japan and the asia oceania regions qzss services were available on a trial basis as of january 12 2018 and were started in november 2018 the first satellite was launched in september 2010 28 an independent satellite navigation system from gps with 7 satellites is planned for 2023 29 comparison of systems edit system beidou galileo glonass gps navic qzss owner china european union russia united states india japan coverage global global global global regional regional coding cdma cdma fdma cdma cdma cdma cdma altitude 21 150 km 13 140 mi 23 222 km 14 429 mi 19 130 km 11 890 mi 20 180 km 12 540 mi 36 000 km 22 000 mi 32 600 km 20 300 mi 39 000 km 24 000 mi 30 period 12 63 h 12 h 38 min 14 08 h 14 h 5 min 11 26 h 11 h 16 min 11 97 h 11 h 58 min 23 93 h 23 h 56 min 23 93 h 23 h 56 min rev s day 17 9 1 888 17 10 1 7 17 8 2 125 2 1 1 satellites beidou 3 28 operational 24 meo 3 igso 1 gso 5 in orbit validation 2 gso planned 20h1 beidou 2 15 operational 1 in commissioning by design 27 operational 3 spares currently 26 in orbit 24 operational 2 inactive 6 to be launched 31 24 by design 24 operational 1 commissioning 1 in flight tests 32 24 by design 30 operational 33 8 operational 3 geo 5 gso meo 4 operational 3 gso 1 geo 7 in the future frequency 1 561098 ghz b1 1 589742 ghz b1 2 1 20714 ghz b2 1 26852 ghz b3 1 559 1 592 ghz e1 1 164 1 215 ghz e5a b 1 260 1 300 ghz e6 1 593 1 610 ghz g1 1 237 1 254 ghz g2 1 189 1 214 ghz g3 1 563 1 587 ghz l1 1 215 1 2396 ghz l2 1 164 1 189 ghz l5 1 17645 ghz l5 2 492028 ghz s 1 57542 ghz l1c a l1c l1s 1 22760 ghz l2c 1 17645 ghz l5 l5s 1 27875 ghz l6 34 status operational 35 operating since 2016 2020 completion 31 operational operational operational operational accuracy 3 6 m or 12 ft public 0 1 m or 3 9 in encrypted 1 m or 3 ft 3 in public 0 01 m or 0 39 in encrypted 2 4 m or 6 ft 7 in 13 ft 1 in 0 3 5 m or 1 ft 0 in 16 ft 5 in no dgps or waas 1 m or 3 ft 3 in public 0 1 m or 3 9 in encrypted 1 m or 3 ft 3 in public 0 1 m or 3 9 in encrypted system beidou galileo glonass gps navic qzss sources 7 using multiple gnss systems for user positioning increases the number of visible satellites improves precise point positioning ppp and shortens the average convergence time 36 the signal in space ranging error sisre in november 2019 were 1 6 cm for galileo 2 3 cm for gps 5 2 cm for glonass and 5 5 cm for beidou when using real time corrections for satellite orbits and clocks 37 the average sisres of the bds 3 meo igso and geo satellites were 0 52 m 0 90 m and 1 15 m respectively compared to the four major global satellite navigation systems consisting of meo satellites the sisre of the bds 3 meo satellites was slightly inferior to 0 4 m of galileo slightly superior to 0 59 m of gps and remarkably superior to 2 33 m of glonass the sisre of bds 3 igso was 0 90 m which was on par with the 0 92 m of qzss igso however as the bds 3 geo satellites were newly launched and not completely functioning in orbit their average sisre was marginally worse than the 0 91 m of the qzss geo satellites 3 augmentation edit gnss augmentation is a method of improving a navigation system s attributes such as accuracy reliability and availability through the integration of external information into the calculation process for example the wide area augmentation system the european geostationary navigation overlay service the multi functional satellite augmentation system differential gps gps aided geo augmented navigation gagan and inertial navigation systems related techniques edit further information satellite geodesy radio techniques doris edit main article doris geodesy doppler orbitography and radio positioning integrated by satellite doris is a french precision navigation system unlike other gnss systems it is based on static emitting stations around the world the receivers being on satellites in order to precisely determine their orbital position the system may be used also for mobile receivers on land with more limited usage and coverage used with traditional gnss systems it pushes the accuracy of positions to centimetric precision and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of earth rotation and deformations in order to build a much more precise geodesic reference system 38 leo satellites edit the two current operational low earth orbit leo satellite phone networks are able to track transceiver units with accuracy of a few kilometres using doppler shift calculations from the satellite the coordinates are sent back to the transceiver unit where they can be read using at commands or a graphical user interface 39 40 this can also be used by the gateway to enforce restrictions on geographically bound calling plans international regulation edit the international telecommunication union itu defines a radionavigation satellite service rnss as a radiodetermination satellite service used for the purpose of radionavigation this service may also include feeder links necessary for its operation 41 rnss is regarded as a safety of life service and an essential part of navigation which must be protected from interferences classification edit itu radio regulations article 1 classifies radiocommunication services as radiodetermination service article 1 40 radiodetermination satellite service article 1 41 radionavigation service article 1 42 radionavigation satellite service article 1 43 maritime radionavigation service article 1 44 maritime radionavigation satellite service article 1 45 aeronautical radionavigation service article 1 46 aeronautical radionavigation satellite service article 1 47 examples of rnss use augmentation system gnss augmentation automatic dependent surveillance broadcast beidou navigation satellite system bds galileo european gnss global positioning system gps with differential gps dgps glonass navic quasi zenith satellite system qzss frequency allocation edit further information frequency allocation the allocation of radio frequencies is provided according to article 5 of the itu radio re...