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The Global Positioning System A Shared National Asset (1995) / Chapter Skim
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Pages 2-6

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From page 2...
... The differences between observed ranges and predicted ranges are used to compute corrections to GPS parameters, error sources, and/or resultant positions. These differential corrections are then transmitted to GPS users, who apply the corrections to their received GPS signals or computed position.
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From page 3...
... . With SA set at zero, the standalone accuracy improves to around 30 meters (95 percent probability)
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From page 4...
... The ground-based communications network ~11 consist of 24 wide-area reference stations, two wide-area master stations, and two satellite uplink sites. Differential corrections and integrity data derived from the ground-based network, as well as additional ranging data, will be broadcast to users from the geostationary satellites using an "L-like" signal.
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From page 5...
... Although GPS currently meets all accuracy requirements for both GPS time transfer and lime synchronization using direct GPS lime, many telecommunications companies are still hesitant to utilize GPS because of concerns about system reliability and the presence of SA. SA has little or no effect on the ability to use GPS for spacecraft orbit or attitude determination, but A-S limits the performance of orbit determination for spacecraft that rely on dual-frequency codeless measurements.
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From page 6...
... Modifications to the Block IlR satellites and the Block ITF request for proposal may be required if upgraded encryption methods are necessary. Changes to military receivers also will be required.
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Key Terms

  • orbit determination
  • collision avoidance
  • accuracy requirements
  • attitude determination
  • time transfer

  • user equipment
  • ranging data
  • earth science
  • differential corrections
  • reference stations

  • gps signal
  • military receivers
  • coast guard
  • science applications
  • determination accuracy

  • precision approach
  • ballistic missile
  • civilian accuracy
  • current level
  • gps receiver

  • gps time
  • differential gps
  • gps signals
  • precise time
  • gps satellite

  • basic gps
  • aviation administration
  • civilian users
  • federal aviation
  • percent probability


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