▁October ▁ 1 9 5 7 , ▁the ▁Soviet ▁Union ▁launched ▁the ▁world ' s ▁first ▁artificial ▁satellite , ▁S put nik . ▁ ▁Scient ists ▁at ▁Joh ns ▁Hop kins ▁University ' s ▁App lied ▁Physics ▁Labor atory ▁took ▁a ▁series ▁of ▁measurements ▁of ▁S put nik ''' s ▁do pp ler ▁shift ▁yield ing ▁the ▁satellite ' s ▁position ▁and ▁velocity . ▁ ▁This ▁team ▁continued ▁to ▁monitor ▁S put nik ▁and ▁the ▁next ▁sat ell ites ▁into ▁space , ▁S put nik ▁II ▁and ▁Explorer ▁I . ▁ ▁In ▁March ▁ 1 9 5 8 ▁the ▁idea ▁of ▁working ▁backwards , ▁using ▁known ▁satellite ▁or bits ▁to ▁determine ▁an ▁unknown ▁position ▁on ▁the ▁Earth ' s ▁surface ▁began ▁to ▁be ▁expl ored . ▁ ▁This ▁led ▁to ▁the ▁TR AN S IT ▁satellite ▁navigation ▁system . ▁ ▁The ▁first ▁TR AN S IT ▁satellite ▁was ▁placed ▁in ▁polar ▁orbit ▁in ▁ 1 9 6 0 . ▁ ▁The ▁system , ▁consisting ▁of ▁ 7 ▁sat ell ites , ▁was ▁made ▁oper ational ▁in ▁ 1 9 6 2 . ▁ ▁A ▁navig ator ▁using ▁read ings ▁from ▁three ▁sat ell ites ▁could ▁expect ▁accuracy ▁of ▁about ▁ 8 0 ▁feet . ▁ ▁On ▁July ▁ 1 4 , ▁ 1 9 7 4 ▁the ▁first ▁prototype ▁Nav star ▁G PS ▁satellite ▁was ▁put ▁into ▁orbit , ▁but ▁its ▁clock s ▁failed ▁shortly ▁after ▁launch . ▁ ▁The ▁N avig ational ▁Technology ▁Sat ellite ▁ 2 ' ', ▁red es igned