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GLOBAL TELECOMMUNICATIONS.

CONSTELLATIONS  OF LOW-ORBITING  satellites  hold  the key  to  today's    flexible   global  telephone  networks .These  systems integrate  satellite   communications  with  existing  land line  and  cellular  network  to provide   truly  global  coverage  from  a  mobile  phone  .This  enables   people, even      in  remote   areas even  those  on  tiny  pacific   islands   or  high  in the  Himalayas   ,to  keep  in  touch  with   rest  of  the  world .Satellite  system s   are  the    next  logical    step    in  the  mobile  -phone  revolution  that  swept  the  world  in  the  late  1990's.
IRIDIUM    was  the  first  system  to  offer   a commercial  service .It  was  conceived   and  developed  by   the  US  electronics company   Motorola   ,and  began  operation  on 1  November  1998.The  system  was  named  after  the  77th  chemical  element in  the periodic Table  ,as there  were  originally to  be  77 satellites  in the   network.Other  networks   offering  a  similar    service  include  Global star  , which  operates  with  a constellations   of  48 satellites.
IRIDIUM  SATELLITE  ORBITAL  NETWORK.
The  Iridium  network  consists  of   66  satellites  ,each  providing  a  coverage  of  16  million square  km (6  million  square mile).It  offers  a  constant  service  ,as  there  will always  be  one    or  more satellite    over  the   horizon  .The   network  operates  as  a  constellations h  means  which  means  that  a  failed  or  malfunctioning  satellite   will  not  impede   the  system's  ability   to  provide global  coverage.When  a  call  is  made  it  is  routed to the   nearest  satellite  ,and   then  relayed  around  the  world  to  its  destination.If  the  destination  is  the  land  based  telephone  , the  last  satellite    in  the  chain    feed  the  signal     to  a"gateway" ground  station  .This  gateway  then  connects   with  the  existing   land line  telephone  system. ,

 

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