Find your lo­ca­tion through GPS!!

Active Kids - - Class Room Discussion -

The Global Po­si­tion­ing Sys­tem (GPS) is a satel­lite nav­i­ga­tion sys­tem that helps in lo­cat­ing a place on the earth.

What is GPS?

The GPS is ac­tu­ally a con­stel­la­tion of 27 Earth-or­bit­ing satel­lites. In this, 24 Satel­lite Ve­hi­cles are in op­er­a­tion and the three are ex­tras ready to work in case any one fails. GPS is owned and op­er­ated by the United States Gov­ern­ment un­der the Depart­ment of De­fense (DoD). The US Pres­i­dent Ron­ald Rea­gan is­sued a di­rec­tive mak­ing GPS freely avail­able for civil­ian use, once it was suf­fi­ciently de­vel­oped, for a common good. The GPS is con­sid­ered a dual-use tech­nol­ogy, mean­ing it has sig­nif­i­cant mil­i­tary and civil­ian ap­pli­ca­tions. The first satel­lite for GPS was launched in 1989 and the 24th one was in 1994. GPS be­came fully op­er­a­tional in 1995. Brad­ford Parkin­son, Roger L Eas­ton and Ivan A Get­ting are cred­ited with in­vent­ing this tech­nol­ogy.

How GPS works?

Each of the 24 so­lar-pow­ered satel­lites cir­cles the globe at about 12,000 miles (19,300 km). They make two com­plete ro­ta­tions ev­ery day. The or­bits are ar­ranged so that at any time, any­where on Earth, there are at least four satel­lites "vis­i­ble" in the sky. The four satel­lites are not evenly spaced (90 de­grees) apart within each or­bit. In gen­eral terms, the an­gu­lar dif­fer­ence be­tween satel­lites in each or­bit is 30, 105, 120, and 105

de­grees apart which sum to 360 de­grees. The Satel­lite Ve­hi­cles or­bit at an al­ti­tude of ap­prox­i­mately 20,200 km at an or­bital ra­dius of ap­prox­i­mately 26,600 km. Each one makes two com­plete or­bits each day, re­peat­ing the same ground track each day. This means that the four Ve­hi­cles are vis­i­ble from one spot for a few hours each day.

Mon­i­tor­ing Sta­tions

The flight paths of the satel­lites are tracked by U.S. Air Force mon­i­tor­ing sta­tions in var­i­ous lo­ca­tions around the world in­clud­ing Hawaii, Kwa­jalein, Atoll, Diego Gar­cia, Colorado, and Cape Canaveral along with shared mon­i­tor sta­tions op­er­at­ing in Eng­land, Ar­gentina, Ecuador, Bahrain, Aus­tralia and Wash­ing­ton DC.

GPS on fin­ger tips

To­day, the GPS re­ceivers come in a va­ri­ety of for­mats - from de­vices in­te­grated into cars, phones, and watches. A GPS re­ceiver cal­cu­lates its po­si­tion by pre­cisely tim­ing the sig­nals sent by GPS satel­lites high above the Earth. Each satel­lite con­tin­u­ally trans­mits mes­sages that in­di­cate the time of the mes­sage trans­mit­ted and the satel­lite po­si­tion at time of mes­sage trans­mis­sion.


A GPS re­ceiver's job is to lo­cate four or more of th­ese satel­lites, fig­ure out the dis­tance be­tween each and use this in­for­ma­tion to de­duce its own lo­ca­tion. This op­er­a­tion is based on a sim­ple math­e­mat­i­cal prin­ci­ple called ‘ Tri­lat­er­a­tion’.

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