Gem 110

• Many satellites were launched since Sputnik, the first satellite by the Russians in 1957 and what followed on was a race with the developed nations on navigation, mapping, communications and weather
• Satellites of concern are positioning and mapping that produced the shape and size of the earth that has enabled us to produce accurate coordinates of points anywhere on of above the earth's surface

  
• USSR launches its first Sputnik satellite into space in October


  1957
• Determining Sputnik's orbit


  Measuring the Doppler frequency curve from one single satellite pass
• Shortly thereafter the US Navy Navigation Satellite System (NNSS) was conceived
• Early research and development was conducted at the John Hopkins University Applied Physics Laboratory
• NNSS system


  Also known as the Transit system
• SECOR (Sequential Collation of Ranges) satellite launched by the US Army


  1960
• SECOR satellite


  • Used for geodesy, to map the whole universe
  • Allowed for improved global mapping and precise positioning of ground stations linking the Island States in the Pacific and continents of the universe

  
• SECOR satellite positioning


  1. Linked to four mobile ground stations: three in accurately determined known locations, and a fourth in an unknown location

  2. Measured satellite's distance from the three known stations to determine its position in space

  3. Ground stations transmitted phase modulated signal to satellite, satellite received and transmitted back

  4. Time taken for signal to travel multiplied by speed of light gave pseudorange distance

  5. Process repeated many times to enhance accuracy, minimum 3 satellite passes sufficient

  
• GPS


  An evolution of the SECOR system where the ground-based transmitters have been migrated into orbit, with many satellites in space transmitting signals to one receiver position on or above the earth's surface
• Precision of SECOR system: Repeatability brought about 5m precision with longer lines up to 1:100,000 i.e. 1m error for 100,000m distance
• Number of SECOR satellites launched: 13, Operational from 1964 to 1969
• Satellite Laser Ranging (SLR) became operational in 1970 and continues to today, measuring distances to satellites equipped with retroreflectors to 1m accuracy
• Transit System operational


  1958-1996
• Transit System


  • First satellite navigation system used operationally
  • Primarily used by US Navy to provide accurate location information to Polaris ballistic missile submarines and for navigation of Navy surface ships, hydrographic survey and geodetic surveying
  • Provided continuous navigation satellite service from 1964, initially for Polaris submarines and later for civilian use as well

  
• Transit System operation


  1. Doppler ranging principle

  2. Satellite motion produced Doppler frequency shift in signal received

  3. Receiver generated reference signal compared to received signal to generate difference frequency

  4. Doppler count measured change in slant range between satellite and user

  5. Position fix used several successive Doppler counts