report of the action team on global navigation satellite systems (gnss)
report of the action team on global navigation satellite systems (gnss)
report of the action team on global navigation satellite systems (gnss)
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• Planet Quest:http://planetquest.jpl.nasa.gov/• U.S. Coast Guard Navigati<strong>on</strong> Center:http://www.navcen.uscg.gov/• U.S. Missi<strong>on</strong> to <str<strong>on</strong>g>the</str<strong>on</strong>g> European Uni<strong>on</strong>: GPS and <str<strong>on</strong>g>the</str<strong>on</strong>g> EU's GALILEO Systemhttp://www.useu.be/Galileo/• U.S. Space Objects Registry:http://www.usspaceobjectsregistry.state.gov/Global Positi<strong>on</strong>ing System descripti<strong>on</strong>22. GPS is a Satellite Navigati<strong>on</strong> System with many milli<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> civil users worldwide. GPSprovides specially coded <strong>satellite</strong> signals that can be processed in a GPS receiver, enabling <str<strong>on</strong>g>the</str<strong>on</strong>g>receiver to compute positi<strong>on</strong>, velocity and time. At least four GPS <strong>satellite</strong> signals are necessaryto compute positi<strong>on</strong>s in three dimensi<strong>on</strong>s and <str<strong>on</strong>g>the</str<strong>on</strong>g> time <str<strong>on</strong>g>of</str<strong>on</strong>g>fset in <str<strong>on</strong>g>the</str<strong>on</strong>g> receiver clock. With aReceiver Aut<strong>on</strong>omous Integrity M<strong>on</strong>itoring (RAIM) capable receiver and six in view GPS<strong>satellite</strong>s allow <str<strong>on</strong>g>the</str<strong>on</strong>g> users to achieve RAIM. The Space Segment <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> system c<strong>on</strong>sists <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> GPS<strong>satellite</strong>s. These space vehicles (SVs) send radio signals from space. The nominal GPSOperati<strong>on</strong>al C<strong>on</strong>stellati<strong>on</strong> c<strong>on</strong>sists <str<strong>on</strong>g>of</str<strong>on</strong>g> 24 <strong>satellite</strong>s plus <strong>on</strong>-orbit spares that orbit <str<strong>on</strong>g>the</str<strong>on</strong>g> Earth in 12hours. There are <str<strong>on</strong>g>of</str<strong>on</strong>g>ten more than 24 operati<strong>on</strong>al <strong>satellite</strong>s as new <strong>on</strong>es are launched to replaceolder <strong>satellite</strong>s.23. The <strong>satellite</strong> orbits repeat almost <str<strong>on</strong>g>the</str<strong>on</strong>g> same ground track (as <str<strong>on</strong>g>the</str<strong>on</strong>g> Earth turns beneath <str<strong>on</strong>g>the</str<strong>on</strong>g>m)<strong>on</strong>ce each day. The orbit altitude is such that <str<strong>on</strong>g>the</str<strong>on</strong>g> <strong>satellite</strong>s repeat <str<strong>on</strong>g>the</str<strong>on</strong>g> same track and c<strong>on</strong>figurati<strong>on</strong>over any point approximately each 24 hours (4 minutes earlier each day). There are six orbitalplanes (with nominally four SVs in each), and inclined at about fifty-five degrees with respect to<str<strong>on</strong>g>the</str<strong>on</strong>g> equatorial plane. This c<strong>on</strong>stellati<strong>on</strong> provides <str<strong>on</strong>g>the</str<strong>on</strong>g> user with between five and eight SVs visiblefrom any point <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> Earth.C<strong>on</strong>trol Segment24. The C<strong>on</strong>trol Segment c<strong>on</strong>sists <str<strong>on</strong>g>of</str<strong>on</strong>g> a system <str<strong>on</strong>g>of</str<strong>on</strong>g> tracking stati<strong>on</strong>s located around <str<strong>on</strong>g>the</str<strong>on</strong>g> world,including <str<strong>on</strong>g>the</str<strong>on</strong>g> GPS Master C<strong>on</strong>trol and M<strong>on</strong>itor Network. The Master C<strong>on</strong>trol facility is located atSchriever Air Force Base (formerly Falc<strong>on</strong> AFB) in Colorado. These m<strong>on</strong>itor stati<strong>on</strong>s measuresignals from <str<strong>on</strong>g>the</str<strong>on</strong>g> SVs, which are incorporated into orbital models for each <strong>satellite</strong>. The modelscompute precise orbital data (ephemeris) and SV clock correcti<strong>on</strong>s for each <strong>satellite</strong>. The MasterC<strong>on</strong>trol stati<strong>on</strong> uploads ephemeris and clock data to <str<strong>on</strong>g>the</str<strong>on</strong>g> SVs. The SVs <str<strong>on</strong>g>the</str<strong>on</strong>g>n send subsets <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>orbital ephemeris data to GPS receivers over radio signals.25. The GPS User Segment c<strong>on</strong>sists <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> GPS receivers and <str<strong>on</strong>g>the</str<strong>on</strong>g> user community. GPSreceivers c<strong>on</strong>vert SV signals into positi<strong>on</strong>, velocity, and time estimates. Four <strong>satellite</strong>s arerequired to compute <str<strong>on</strong>g>the</str<strong>on</strong>g> four dimensi<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> X, Y, Z (positi<strong>on</strong>) and Time.26. GPS receivers are used for navigati<strong>on</strong>, positi<strong>on</strong>ing, time disseminati<strong>on</strong>, remote clockcomparis<strong>on</strong> and for o<str<strong>on</strong>g>the</str<strong>on</strong>g>r research purposes. Navigati<strong>on</strong> in three dimensi<strong>on</strong>s is <str<strong>on</strong>g>the</str<strong>on</strong>g> primaryfuncti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> GPS. Navigati<strong>on</strong> receivers are made for aircraft, ships, ground vehicles and for handcarrying by individuals. Enhanced positi<strong>on</strong>ing is possible using GPS receivers at referencelocati<strong>on</strong>s providing correcti<strong>on</strong>s and relative positi<strong>on</strong>ing data for remote receivers. Surveying,geodetic c<strong>on</strong>trol, and plate tect<strong>on</strong>ic studies are some examples.8