Global Positioning Systems

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Global Positioning Systems

• Equipment and Technology

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Before GPS

• A sextant is used to make precise celestial
  observations of the Sun, stars, and planets. It
  measures height, in degrees, above the horizon,
  which is used with the exact time to calculate
  position. The sextant shown here was made in the
  first half of the 19th century. "Shooting the
  stars" remains a basic skill for the sea-going
  navigator.

• TRANSIT was the first operational satellite
  positioning system. Six satellites gave worldwide
  coverage every 90 minutes and provided positions
  that were accurate to within 200 meters (660
  feet). Positions were obtained by measuring the
  Doppler shift of the satellite signal. TRANSIT
  was effective, but it was limited by low accuracy
  and lack of 24-hour availability. The TRANSIT
  system operated until 1996.

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GPS Satellite

• GPS satellite launches began in 1978, and a
  second-generation set of satellites ("Block II")
  was launched beginning in 1989. Today's GPS
  constellation consists of at least 24 Block II
  satellites. The system became fully operational
  in 1995.

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Military Equipment

• One of the first portable GPS units available to
  soldiers in the field was the PSN-8 "Manpack"
  receiver. About 1,400 were manufactured between
  1988 and 1993.

• The Manpack was replaced in 1993 by the hand-held
  Precision Lightweight GPS Receiver (PLGR),
  popularly known as the "Plugger." These units are
  similar to civilian receivers, but they can use
  higher-precision GPS signals.

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GPS for the Public

• This GPS receiver incorporates such capabilities
  as navigation tools, internet access, and a
  digital camera.

• Many types of GPS systems can be used on
  vehicles, providing the driver with the current
  position and a local map.

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• All information and images provided by
• The Smithsonian National Air and Space Museums
  Website