Feature

Satellite navigation today


 
GPS
 
 
There are two satellite navigation systems already available. The specifications of these two systems are given below.
 
GPS – United States
  
 
 
 GPS - United States
  
  • a standard constellation of 24 satellites
  • civil use allowed
  • free of charge for the foreseeable future
  • 20 m horizontal accuracy 95% of time with selective availability off (16 M horizontal accuracy for military applications)
     
     
     
    Glonass
     
    		 

    GLONASS – Russia
      

    • when fully operational a constellation of 24 satellites
    • civil use allowed
    • free of charge for the foreseeable future
    • 60 m horizontal accuracy 99.7% of time

    The American GPS and Russian GLONASS satellite constellations were originally designed for military purposes in order to provide military forces with extremely accurate positioning information.

    The current capabilities of GPS and GLONASS, although very adequate for some user communities, present some shortfalls. First, the lack of civil international control presents a serious problem from the institutional point of view. Second, GPS or GLONASS cannot meet all civil aviation requirements for precision and non-precision approach phases of flight. In addition, marine and land users will also require some sort of augmentation for improving GPS / GLONASS performances.

    The first generation Global Navigation Satellite System (GNSS-1), as defined by the experts of the ICAO/GNSS panel, plans for some system augmentations in addition to the basic GPS and GLONASS constellations in order to achieve the level of performance suitable for civil aviation applications.
     
     
      
    Last update: 9 November 2001


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    More about...

     •  How existing satellite navigation systems work (http://www.esa.int/esaNA/ESA5JYZK0TC_index_0.html)
     •  Limitations of existing systems (http://www.esa.int/esaNA/ESAEKYZK0TC_index_0.html)
     •  Meeting users' requirements (http://www.esa.int/esaNA/ESA7LYZK0TC_index_0.html)
     •  What is EGNOS? (http://www.esa.int/esaNA/GGG63950NDC_egnos_0.html)
     •  How does EGNOS work? (http://www.esa.int/esaNA/GGGQI950NDC_egnos_0.html)
     •  EGNOS for Professionals (http://www.esa.int/navigation/egnos-pro)