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Dual satellite navigation system and method

  • US 5,126,748 A
  • Filed: 05/20/1991
  • Issued: 06/30/1992
  • Est. Priority Date: 12/05/1989
  • Status: Expired due to Term
First Claim
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1. A method of airborne object position determination using a pair of earth orbiting satellites (S1 and S2) and a fixed station whose positions are known in an Earth-Centered-Earth-Fixed (ECEF) coordinate frame and in which the distance from the center of the earth to any location on the surface of the earth (L3s) is known within said ECEF coordinate frame, comprising the steps of:

  • simultaneously transmitting from a fixed station first and second forward periodic signals, synchronized to a fixed station forward transmission clock, via first and second satellites (S1 and S2) respectively to an object whose position is to be determined;

    receiving said first and second forward signals at said object, said first forward signal bearing information indicative of a future time frame at which said object will begin transmitting a return signal according to an object clock synchronized to said first forward signal as received at said object;

    measuring at said object a percent phase offset of a total modulation period between similar portions of received carrier modulation of said first and said second forward signals, said percent offset corresponding to a first relative time difference in said first and second forward signals as received at said object;

    transmitting from said object via said first satellite to said fixed station said return signal encoded with information indicative of said first relative time difference;

    measuring at said fixed station a round trip delay where said round trip delay is a second relative time difference between said fixed station forward transmission clock and a fixed station return reception clock synchronized with said return signal as received at said fixed station;

    calculating a first distance (L1) from said first satellite to said object according to said round trip delay;

    calculating a second distance (L2) from said second satellite to said object according to said round trip delay and said first relative time difference;

    measuring an altitude (L3a) of said object from a location on the surface of the earth;

    combining said measured altitude (L3a) with a known distance from said location to the center of the earth (L3s) to obtain a third distance (L3); and

    calculating a position of said object within said ECEF coordinate frame according to said first, second and third distances.

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