TheBasicsof GPS
GPS,or GlobalPositioningSystem,is a satellitenavigationsystem designedto provideworldwidepositioningandtime informationwith
all weathercapabilityquick. responsetime andaccuracyto within severalyards.GPS is maintainedby the United StatesDepartmentof Defense24 hoursa day.
GPSis a systemof 24 satellitesorbitingat an altitudevery high abovetheearth.Becauseof thegreataltitude,thesatellites'signals arenot interferedwith by the terrainor geography,andthe high frequencyof the signals(
GPSusestheprincipleof rangingto give you yourposition.This is doneby measuringthedistancefiom your positionto thepositionof at leastthreesatellitesThe. distanceto a satelliteis calculatedby measuringhow long it
The satellitesandthe Star Pilot must be preciselytirnedto generate the exactsameradio signalat the exactsametime in orderto measure the time anddistancecalculationswith a high degreeof accuracy. This is accomplishedby the useof atomicclockson all the satellites, andby comparingwhat part of the radiosignalcodeis receivedat the exactsametime from all the satellites.
To completeits calculationsfor your position,theStar Pilot looksup in its databasetheknownpositionof eachof thesatellitesat that exacttime.BecausetheGPSsatellitesarein sucha high orbit,their positionsat any giventime arequitepredictableNow. . all theStar Pilot needsto do is calculateall thistor threeor four satellitesevery few seconds,andyou
GPSsatellitesareconstantlymonitoredby Departmentof Defense groundstationsSatellite.clocksandexactpositioninginformationis computedandany variationsarenotedor comectedasnecessaryand. transmittedto theappropriatesatellitesOther.possiblesourcesof errors,suchasatmosphericdragandgeometricpositionmeasurement discrepancies,areeliminatedby the sophisticated,mathematical programmingwithin the Star Pilot GPS system.
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