History of satellite

• GPS


  Global Navigation Positioning System

  
• Calculations using general relativity determined that the clocks on GPS satellites would be seen by Earth's observers to run 38 microseconds faster per day, and this was corrected for in the design of GPS
• Natural Satellite


  A natural satellite is a celestial body that orbits a planet or other body larger than itself and is not man-made
• The Soviet Union launched the first man-made satellite, Sputnik


  1957
• Tracking Sputnik's radio transmission

  1. Physicists William Guier and George Weiffenbach at Johns Hopkins's Applied Physics Laboratory monitor Sputnik's radio transmission

  2. They realized they could pinpoint where the satellite was along its orbit due to the Doppler effect

  3. This led them to develop the inverse problem - pinpointing the user's location given that of the satellite
• Transit first navigation system successfully tested

  1960
• Transit navigation system


  • Uses 5 satellites
  • Could provide a navigational fix approximately once per hour
• Transit navigation system operation

  1. Satellites tracked by a series of ground stations and a command center

  2. Operates on Doppler ranging principle

  3. Motion of the satellite relative to the user produces a Doppler frequency shift

  4. User's receiver generates a reference signal and compares it to the received signal to generate a Doppler count

  5. Doppler count is a measure of the change in the slant range (distance) of the satellite and the user
• Strengths of Transit


  • Requires only 4 satellites
  • A position fix required only one satellite at a time
  • Satellites in circular, low polar Earth orbits
• Disadvantage of Transit


  • A position fix could take 30 minutes to compute, and any motion of the receiver complicated the position calculation
• Transit system components


  1. Tracking station

  2. Computing centre

  3. Injection station

  4. The user
• United States Army orbited its first Sequential Collation of Range (SECOR) satellite used for geodetic surveying


  1964
• SECOR system


  • Included three ground-based transmitters from known locations that would send signals to the satellite transponder
  • A fourth ground-based station at an undetermined position could use those signals to fix its location precisely
• U.S. Navy developed the Timation satellite that proved the ability to place accurate clocks in space


  1967
• Ground-based Omega Navigation System became the first worldwide radio navigation system


  1970s
• Limitations of ground-based navigation systems drove the need for a more universal navigation solution with greater accuracy
• Nuclear triad


  Consisted of the United States Navy's submarine-launched ballistic missiles (SLBMs), United States Air Force (USAF) strategic bombers and intercontinental ballistic missiles (ICBMs)
• Accurate determination of the SLBM launch position was a force multiplier for the nuclear deterrence posture
• Precise navigation would enable United States submarines to get an accurate fix of their positions before they launched their SLBMs
• The USAF also had requirements for a more accurate and reliable navigation system
• To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms, which required the ability to fix the launch position
• The Air Force proposed a radio-navigation system called MOSAIC (MObile System for Accurate ICBM Control)


  1960

  
• Project 57 study led to the GPS concept being born


  1963
• The United States Army orbited its first Sequential Collation of Range (SECOR) satellite

  1964
• Decades later, during the early years of GPS, civilian surveying became one of the first fields to make use of the new technology, because surveyors could reap benefits of signals from the less-than-complete GPS constellation years before it was declared operational
• GPS can be thought of as an evolution of the SECOR system where the ground-based transmitters have been migrated into orbit
• SECOR has its mark in PNG on one of the Global Geodetic Campaigns (On WGS72 Satellite System)

  
• WGS60


  Developed from LOREN, SECOR and Triangulation network with Astronomy observation, Satellites and Stella Observations

  
• WGS66


  In January 1966, a World Geodetic System Committee composed of representatives from the Army, Navy, and Air Force was established to develop a new World Geodetic System

  
• Another important predecessor to GPS came from a different branch of the United States military
• WGS66 development


  1. In January 1966, a World Geodetic System Committee composed of representatives from the United States Army, Navy and Air Force, was charged with the responsibility of developing an improved WGS

  2. Large amounts of Doppler and optical satellite data had become available since the development of WGS60

  3. Using the additional data and improved techniques, WGS 66 was produced which served DoD needs for about five years after its implementation in 1967
• WGS66 Ellipsoid


  • Flattening (1/298.25), determined from satellite data
  • Semimajor axis (6,378,145 meters), determined from a combination of Doppler satellite and astro-geodetic data
  • Worldwide 5° × 5° mean free air gravity anomaly field provided the basic data for producing the WGS 66 gravimetric geoid
  • A geoid referenced to the WGS 66 Ellipsoid was derived from available astrogeodetic data to provide a detailed representation of limited land areas
• Transit


  • 7 low-altitude polar-orbiting satellites that broadcast very stable radio signals
  • Several ground-based monitor stations to track the satellites
  • Facilities to update satellite orbital parameters
• Transit users


  Determine their position on earth by measuring the Doppler shift of signals transmitted by the satellites

  
• Originally designed to meet the Navy's requirement for locating ballistic missile submarines and other ships at the ocean's surface, Transit was made available to civilian users in 1967
• The concept for Transit evolved from observations of the Russian satellite Sputnik in 1957
• Researchers at the Applied Physics Laboratory (APL) discovered that measurements of the Doppler shift as the satellite passed by were adequate to determine the entire satellite orbit
• Dr. Frank T.McClure of APL noted that conversely, if the satellite orbit were known, position on the earth could be determined using these same Doppler measurements
• WGS72


  After an extensive effort extending over a period of approximately three years, the Department of Defense World Geodetic System 1972 was completed
• WGS72 development


  1. Selected satellite, surface gravity and astrogeodetic data available through 1972 from both DoD and non-DoD sources were used in a Unified WGS Solution (a large scale least squares adjustment)

  2. The results of the adjustment consisted of corrections to initial station coordinates and coefficients of the gravitational field